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An investigation on the influence of the shape of the vortex generator on fluid flow and turbulent heat transfer of hybrid nanofluid in a channel
Abstract
The purpose of this study is to numerically investigate flow field and turbulent heat transfer of hybrid nanofluid, water–DWCNT–TiO2 in a two-dimensional rectangular channel with triangular and semicircular vortex generators with three different heights of 1, 2 and 3 mm. For numerically modeling this study, SIMPLEC algorithm was used. Therefore, initially, the geometry of channel and the grid points were generated, and then for solving the mathematical equations via finite volume method, ANSYS Fluent was used. The results indicate that with an increase in Reynolds number and volume fraction (φ) of nanoparticles, the average Nusselt number increases. Also, with an increase in the φ, the pressure loss in the channel increases. About the geometrical shape of the vortex generators, results indicate that with using the semicircular vortex generator, average Nusselt number is higher compared to that of triangular vortex generator. Also, by investigating the performance evaluation criteria of thermal–hydraulic, which is a criterion for comparing the positive effect of the Nusselt number increase with the negative effect of pressure drop, results indicate that this criterion is higher for the semicircular vortex generator.
... Some of the flows in finned, baffled, and/or ribbed channels under various situations are shown in tab. 1. The indicated technique leads to lengthening the flow path, enhancing turbulence, creating strong recirculation regions, and increasing the heat transfer area, which leads to a good improvement in thermal performance [6][7][8][9][10]. Ahmed et al. [6] Using vortex generators and nanofluids, heat transport in non-circular ducts is improved ...
... Zheng et al. [8] An analysis of the effects of the vortex generator's shape on the turbulent heat transfer of Water/DWCNT-TiO 2 in a channel ...
This paper's numerical study, which applies the finite volume approach and
SIMPLE algorithm, aims to dynamically analyze airflow through a channel with
Z-obstacles. Three distinct models were used to place the Z-barriers inside
the channel. According to Demartini et al.'s model (2004) and as depicted in
example A from the present analysis, the first Z-barrier (fin) is attached
to the top wall (heated) and the second (baffle) to the bottom wall
(insulated). The Z-barriers, on the other hand, were positioned in the
second model on the same wall (in-line arrangement), either on the top
surface (two fins in example B) or on the bottom wall (two baffles in
example C). With the help of these studies, fluid dynamics in solar air
collectors with barriers will be better understood and designed.
... From that figure can be analysed that the addition of ZnO nanofluid to the horizontal flat tube radiator conditions got the highest increase in heat transfer enhancement among other nanofluids, and SiO2 gets the lowest value due to its low thermal conductivity [105]. Table 4 present the thermal properties for some nanoparticle materials [106][107][108][109][110][111][112]. Khan and Ahmed [105] analysed numerically the performance of four different nanoparticles (Al2O3, TiO2, ZnO, SiO2) suspended in water in a horizontal flat tube radiator. ...
This review describes and compare the recent studies for numerical and experimental researches in the improvement of Nanofluid on flow, thermal conductivity, and heat transfer for various heat exchanger applications. The Nanofluid consists of two parts which are nanoparticles and base fluid. This study investigated nanoparticles' and base fluid's effects separately—the main preparation techniques and latest heat exchanger applications that used nanofluid technology, which has been touched upon. Nanofluid technology is one of the hot topics and high Impact that researchers have worked on in the latest decades. Therefore, this review paper investigated and collected the data from the latest results in this area based on nanofluid characteristics and effects of particle material, volume concentration, particle size, particle shape, fluid temperature, acidity, magnetic field, and electrical pulsing individually. Many recent studies were recast using a common parameter to settle comparisons of data between the research group in the same study and conditions to identify its thermal enhancement. The latest trends of nanofluid technology have been stated in this research alongside the recommendations for future studies that present the leaks in each area of study. Heat transfer enhancement has been increased in different nanofluids, metallic, non-metallic, organic, inorganic and hybrid, by up to 300%.
... Several instances exist in the biological, biomedical, and food-preserving areas [1]. Zheng et al. [2] studied the influence of the vortex-producer system in different fluids also the thermal conversion of HNFs in a channel. D'D'D'Ippolito et al. [3] considered the confrontation in the flow in an open channel due to vegetation in their study. ...
... Following these considerations and the Tiwari and Das 35 nanofluid model, we have: Table1. Physical and thermal properties of ethylene glycol (working fluid), SWCNTs, and DWCNTs (nanoparticles) [40][41][42] : where in Eq. (5), q w = T 1 x r * y s * . Further, the non-dimensional similarity transformations are listed below: ...
Carbon nanotubes (CNTs) are nanoscale tubes made of carbon atoms with unique mechanical, electrical, and thermal properties. They have a variety of promising applications in electronics, energy storage, and composite materials and are found as single-wall carbon nanotubes (SWCNTs) and double-wall carbon nanotubes (DWCNTs). Considering such alluring attributes of nanotubes, the motive of the presented flow model is to compare the thermal performance of magnetohydrodynamic (MHD) mono (SWCNTs)/Ethylene glycol) and hybrid (DWCNTs- SWCNTs/Ethylene glycol) nanofluids over a bidirectional stretching surface. The thermal efficiency of the proposed model is gauged while considering the effects of Cattaneo-Christov heat flux with prescribed heat flux (PHF) and prescribed surface temperature (PST). The flow is assisted by the anisotropic slip at the boundary of the surface. The system of partial differential equations (PDEs) is converted into a nonlinear ordinary differential system by the use of similarity transformations and handled using the bvp4c numerical technique. To depict the relationship between the profiles and the parameters, graphs, and tables are illustrated. The significant outcome revealed that the fluid temperature rises in the scenario of both PST and PHF cases. In addition, the heat transfer efficiency of the hybrid nanoliquid is far ahead of the nanofluid flow. The truthfulness of the envisioned model in the limiting scenario is also given.
... In a channel, Zheng. et al. [30] looked at how constructing a vortex generator affected the flow of fluids and the heat evolution of hybrid nanofluids. In all research areas, fractional calculus has recently been used as a tool. ...
Nanofluids can be used in different solar thermal systems. Solar energy devices utilized in industries and nanofluids as a source of solar energy in thermal engineering are two other sources of solar energy, according to the article. This work inspects a viscous, incompressible nanofluid made of different (graphene oxide (GO) and molybdenum disulfide (MoS2)) nanoparticles suspended in carboxymethyl cellulose (CMC). The governed model also considers permeability and angled magnetic effects. Due to memory effects, classical derivatives cannot explore and estimate the physical significance of several fluid limitations. We have addressed the issues with nanofluid suspension using the Prabhakar fractional derivative definition, the quickest and latest modern fractional technique. First, the governed leading equations are transferred to a fractional version using the integral transform technique and Laplace transform, and then it is resolved with various numerical approaches. Each constraint visual impact and significance are analyzed by varying their considered values. The numerical influences of the heat and flow rate are observed at multiple time values. Therefore, we deduce that the momentum and heat profiles are slowed as the Prabhakar fractional restraints increase. While with the increment in the radiation parameter, the velocity profile shows an increasing behavior. Furthermore, the impact of graphene oxide-based suspension is more significant than molybdenum disulfide nanofluid on all governed equations due to the physical features of the considered nanoparticles.
... Another approach in the research of NFs is the use of magnetic NPs and therefore, the hydrodynamic characteristics of the new fluids can be controlled by applying an external MF [32,33] and investigating under the Magnetohydrodynamics (MHD) branch [34]. MHD is a branch of physics devoted to studying the motions of fluids that conduct electricity in the presence of magnetic fields. ...
The aim of this study is to examine the hydrothermal behavior of Fe3O4 Ferrofluid flowing under the effect of uniform magnetic field (0 T ≤ B ≤ 0.3 T). In addition, magnetic field locations were changed for each experiment to observe effect of the magnetic field locations (x/D = 20, 40, 60) on the hydrothermal behavior of the proposed system. Fe3O4 Ferrofluid was prepared in φ = 1.0% volume concentration in water and flows under the laminar regime (1131 ≤ Re ≤ 2102). Comparisons of the hydrothermal behavior of the novel proposed parameters were performed according to combinations of the different magnetic field locations and magnitudes. It is concluded that the highest Nusselt number was obtained using B = 0.3 T for the magnetic field location of x/D = 20 for both in smooth and dimpled tubes. Compared to B = 0 T, the Nusselt number enhancement was detected by 64.03% for smooth tube for the magnetic field location of x/D = 20 for B = 0.3 T whereas Nusselt number wasaugmented by 45.40% for dimpled tube for the same input parameters. Furthermore, no considerable changes in friction factor was determined under magnetic field effect when the application of magnetic field locations was changed. As a result of these findings, the highest increase in Performance Evaluation Criteria belonging dimpled tube was calculated by 33.54% at Re = 2102 for B = 0.16 T for the magnetic field location of x/D = 20. As a general conclusion, this study can shed light on investigating ferrofluids behavior under magnetic field applied in variable magnetic field locations.
... The non-Newtonian fluids posses the diverse nature from Newtonian fluids due to their complex rheological properties. Nanofluids have recently emerged as an important area ____________ * Corresponding author, e-mail: minc@firat.edu.tr in nanotechnology [1][2][3], attracting physical scientists. Due to their high thermal conductivity, clay nanoparticles play an important role in oil and gas drilling. ...
The purpose of this paper to explain the role and importance of fractional
derivatives for mass and heat transfer in Casson nanofluids including clay
nanoparticles. These particles can be found in water, kerosene, and engine
oil. The physical flow phenomena are illustrated using PDE and
thermophysical nanoparticle properties, and this paper addresses the Casson
fractional fluid along with chemical reaction and heat generation. The heat
and mass fluxes are generalized using the constant proportional Caputo
fractional derivative. The present flow model are solved semi-analytically
using the Laplace transform. We generated several graphs to understand how
various flow factors affect velocity. The acquired results reveal that
fractional parameters have dual behavior in velocity profiles. Velocity and
temperature are also compared to previous studies. Compared to the other
fractional derivatives results, field variables and proposed hybrid
fractional derivatives showed a more decaying trend. Furthermore,
significant results of clay nanoparticles with various base fluids have
been obtained.
... The addition of two or more distinct nanoadditives to the base fluid causes the formation of hybrid nanofluid [1,2]. Ali et al. [3] discussed the Maxwell hybrid nanofluid with pressure gradient in a vertical channel. Khalid et al. [4] solved a problem related to nanofluid with ramped conditions. ...
In this paper a free convection unsteady Brinkmann hybrid nanofluids
including two or more nanoadditives to the host liquid is investigated. The
physical flow phenomena are illustrated using PDE and thermophysical
nanoparticle properties, and this paper addresses the Brinkmann fractional
fluid along with chemical reaction and heat generation with ramped
conditions over an inclined vertical plate. The heat and molecular fluxes
are generalized using the novel fractional derivative. The present flow
model are solved semi-analytically using the Laplace transform. The effects
of different parameters specially fractional parameter are deliberated and
plotted graphically. The acquired results reveal that fractional parameters
have dual behavior in velocity profiles and temperature profile. Velocity
and temperature are also compared to previous studies. Compared to the other
fractional derivatives results, field variables and proposed hybrid
fractional derivatives showed a more decaying trend.
... Vortex generators (VGs) have been touted as one of the most effective devices to mitigate or delay flow separations and their associated effects, on top of the ease in their implementation. Generally accepted to be geometrically simple, robust, and costeffective solutions, VGs tend to confer satisfactory flow separation control capabilities, especially if they were optimized for the precise flow separation scenarios appropriately, as can be seen in recent studies by Hu et al. (2018), Yang et al. (2020), Xie and Lee (2020), and Zheng et al. (2021). One of the most important flow structures produced by VGs are the coherent streamwise vortices that re-energize wall boundary layers such that they become more resilient against flow separations, as studies by Lögdberg et al. (2009), Urkiola et al. (2017), and Wang and Ghaemi (2019a, b) have previously shown. ...
In this study, streamwise vortex structures produced by wishbone vortex generators (VGs) and their interactions with a 30° backward-facing ramp (BFR) are investigated to understand their impact upon BFR flow separation behavior at Re = 3 × 10^6. In particular, the effects of skewing the VGs relative to the free-stream are considered and results compared to those reported for vane-type VGs previously. Near-field formations of and interactions between the primary streamwise, horseshoe, and edge vortices are clarified along with the stagnation points and recirculating regions, where they are sensitive towards the VG skewness angle. Streamwise vortex-core strengths, trajectories, and other characteristics are also quantified. While the formations and behavior of streamwise vortices by wishbone and vane-type VGs imposed on a BFR are generally similar, there exist certain key differences. Comparisons with earlier studies show that vane-type VGs tend to produce far more persistent streamwise vortices with stronger circulation levels, while wishbone VGs tend to produce weaker streamwise vortices that convect slightly closer to the BFR surface. Interestingly, numerical predictions show that multiple streamwise vortices produced by a wishbone VG array interact more significantly than its vane-type counterpart even at a small skewness angle of 10°. This leads to much larger reattachment length reductions along the BFR span and potentially offers considerable pressure drag reduction levels.
... Yang et al. [26] examined the flow of water-based hybrid nanofluids across a flexible surface containing a magnetic dipole. Some more studies are given in the references [27][28][29][30][31][32] on the hybrid nanofluid with various geometrical configurations and body forces. ...
The main theme of the present study is to analyze numerically the effects of the magnetic field on the hybrid nanofluid flow over a flat elastic surface. The effects of the thermal and velocity slips are also analyzed in view of the hybrid nanofluid flow. It is considered a combination of titanium oxide (TiO2) and copper oxide (CuO) nanoparticles that are suspended in the incompressible and electrically conducting fluid (water). The behavior of the Brownian motion of the nanoparticles and the thermophoretic forces are contemplated in the physical and mathematical formulations. Moreover, the impact of the Joule heating and viscous dissipation are also discussed using the energy equation. The mathematical modeling is simulated with the help of similarity variables. The resulting equations are solved using the Keller–Box method with a combination of finite difference schemes (FDSs). Hybrid nanofluids provide significant advantages over the usual heat transfer fluids. Therefore, the use of nanofluids is beneficial to improve the thermophysical properties of the working fluid. All of the results are discussed for the various physical parameters involved in governing the flow. From the graphical results, it is found that the hybrid nanoparticles improve the concentration, temperature, and velocity profiles, as well as the thickness of the relevant boundary layer. The conjunction of a magnetic field and the velocity slip, strongly opposes the fluid motion. The boundary layer thickness and concentration profile are significantly reduced with the higher levels of the Schmidt number.
... According to the literature, the length of the entrance (value of l as seen in Fig. 1) must be five times the tube diameter for a turbulent flow [56]. However, here, the length of the entrance is lower than five times the tube diameter but concerning the total length of the tube, it has little effect on the flow [57,58]. The ratio of the root-mean-square of the velocity fluctuations to the mean flow velocity to define the turbulence intensity was considered 5% here. ...
This paper numerically investigates the forced convection and entropy generation of Fe3O4 water nanofluid inside a cylindrical tube with porous hemisphere media. The flow regime is turbulent under a uniform magnetic field and constant heat flux, and to solve the equations, the finite volume method is applied. The combination of nanofluid, magnetic field and porous hemisphere media on the flow and heat transfer in a tube is the main novelty. The effects of different parameters such as Reynolds number (10,000 to 25,000), porosity (ε = 20%, 40%, and 80%.), the solid volume fraction of nanofluid (0.5 vol%, 1 vol%, and 2.5 vol%), friction factor and entropy generation of Ferro-nanofluid in the tube are investigated. The Nusselt number, entropy generation, and friction factor have been discussed and analyzed detailly. It is found that as the Reynolds number enhances, the effect of inertial forces becomes more dominant. Furthermore, by increasing the porosity to 0.8, the Nusselt number decreases to a minimum value. Heat transfer enhancement by increasing Hartmann's number is less effective than adding nanoparticles. A more significant Hartmann number and larger nanoparticle volume fraction lead to more extensive performance evaluation criteria. It is also found that adding a magnetic field increases the friction factor. Adding nanoparticles to the pure water decreases entropy generation by heat transfer per unit volume.
... Zhang et al. (2020) numerically examined the influence of the attack angle and length ratio of RWVGs on the thermal-hydraulic performance, whose outcome certified respective 54%-118% and 152%-568% increases of heat transfer and pressure drop for parallel placement as well as respective 60%-118% and 141%-644% for V-shaped placement. A numerical analysis on a nanofluid-filled twodimensional rectangular channel with triangular and semicircular VGs by Zheng et al. (2020), where average Nu of semicircular VG was higher than that of triangular one. A 15 • VG inclination angle at 0.6, 0.7, 0.8, and 0.9 ellipticity ratios harvested more benefit compared with the original heat exchanger in Wang et al. (2021). ...
Fin-and-flat tube heat exchangers are widely applied to construction vehicles due to native advantages. An elementary unit out of such one was numerically compared with the corresponding experimental validation to secure accuracy, then, saw-tooth vortex generators were introduced to the rear of the tube, and further analyzed under the same configuration. JF factors from two models were utilized to confirm the initial expectation for a higher comprehensive performance, which also encouraged the following L18(3⁶) orthogonal test on wing width (ww), wing height (sw), blade height (sb), flow attack angle (Gf), installation angle (Gi), and saw-tooth number (Ns) for signal-to-noise ratio and contribution rate (CR). The results stated that the numerical implementation could be capable of the following analyses with the maximum errors of 5.00% for heat transfer coefficient and 5.33% for pressure loss, and also corroborate performance enhancement with a JF increment of 29.9% in the following comparison. The CRs of Gi, Ns, sw, ww, Gf, and sb are 30.39%, 19.61%, 15.69%, 13.73%, 10.78%, and 9.80%, respectively.
... ere are several instances in the biochemical and biomedical industries, as well as in the food processing industry [51]. e impact of a vortex generator shape on liquids and the heat transition of hybrid nanofluids in a channel were examined by Zheng et al. [52]. On the scientific scale, D'Ippolito et al. [53] investigated the resistance of open channel flow due to vegetation. ...
In this paper, MHD Brinkman-type fluid flow containing Titanium dioxide and silver nanoparticle hybrid nanoparticles with generalized Mittag-Leffler kernel based fractional derivative is investigated in the presence of bio convection. The governing equations with dimensional analysis and fractional approach are obtained by using the fractional Fourier’s law for heat flux and Fick’s law for diffusion. As a result, bio convection Rayleigh number which is responsible for decline the fluid velocity and fractional parameters use to control the thermal and momentum boundary layers thickness of fluid properties. The obtained solutions can be beneficial for proper analysis of real data and provide a tool for testing possible approximate solutions where needed.
... Many techniques have been tried to enhance the heat transfer, such as making rough surfaces, extending surfaces, or adding twisted tape inside the channels. One effective approach is to add a vortex generator (VG) to make the thermal boundary layer thinner [1][2][3][4][5] by introducing additional turbulence [6] . There are two types of VGs, passive VG and active VG. ...
It has been demonstrated that flexible vortex generators, e.g., flapping flag, can significantly enhance heat transfer inside a heat sink. However, their heat transfer enhancement is only effective when they exhibit flapping behaviors, which require a flow velocity higher than the heat sink working velocity, and thus restraint their application. Minimizing the critical flapping velocity of the flags without sacrificing the heat transfer performance is needed. In this work, we study the cases of inverted flags with different thicknesses in a channel flow. Three flag motion modes are identified by a high-speed camera with increasing flow velocity. In the first mode transition, i.e., the flag starts flapping, the heat dissipation has the highest enhancement. Numerical simulation reveals that compared to the other motion modes, the flapping mode has the strongest average vorticity along the channel wall, leading to the highest heat dissipation among all flag motion modes. Experimental results show that the critical velocity can be as low as 1.5 m/s, at which the heat dissipation enhancement can be as high as 100%. The findings in this work significantly benefit the application of flexible vortex generators in heat sinks, by enabling a decrease in critical velocity and a good enhancement in heat dissipation.
... Using VGs which are on surface walls is regarded as an HTR method which is somehow passive. With the flow of a fluid from some channel having VGs, the flow gets turbulent owing to the rotational regions growth in the vicinity of the VGs, thus resulting in the NF mixture as well as improvement of HTR [7][8][9][10][11][12][13][14]. Parsaeimehr et al. [15] focused on simulating the turbulent flow as well as Al 2 O 3 -H 2 O NF HTR in some rectangular VG channel. ...
The current research investigated the turbulent flow field as well as heat transfer rate (HTR) of the non-Newtonian H2O-Al2O3-carboxymethyl (CMC) in some channel having vortex generators (VGs). The partial differential equations were solved using the finite volume approach and the SIMPLE algorithm. The results also revealed that the VG depth change, which was in a few millimeters range, had no considerable impacts on the Nu as well as pressure decrease. In addition, the rise of Re (higher turbulent flow) remarkably increased HTR. Furthermore, due to the formation of vortex movements, local Nu variations revealed a significant rise near the considered VG. With the increase of the VG attack angle, there was a sudden the fluid flow change in the VG zone, resulting a larger DP, especially for the angle of attack of 60°For the 60° attack angle, a number of vortexes were formed behind the VGs, resulting a sudden variation of velocity on the contact surface of the VG. The greatest Nusselt number was 51.321, and the maximum pressure drop was 94993, according to the artificial neural network findings. As a consequence of the Pareto findings, there is a greater pressure decrease when there are more Nusselt.
... Introducing additional turbulence is one of the possible techniques for enhancement [1] and this approach can be further classified into active and passive tech-niques. Passive techniques usually involve making rough surfaces, extended surfaces or displaying stationary vortex generator inside the channels that disrupt the thermal boundary layer by reducing its thickness [2][3][4][5][6] . Built-in stationary delta winglets as a passive vortex generator have been shown to improve the heat transfer by 2.5 times [7] or the overall heat dissipation rate by 20-35% [8] . ...
The use of flags as vortex generators inside heat sinks has been successfully demonstrated as a heat transfer enhancement technique. However, their thermal-hydraulic performance is usually diminished by the blocking effect induced by the fluttering phenomenon. To tackle this problem, with the expectation to maximize the fluid mixing while minimizing the pressure drop, we report a simple and direct design by splitting a flag into multiple strips. Flags with different strip widths were compared with a full flag on the performance of pressure drop and heat transfer. A high-speed camera is used to investigate their fluttering motion. A piezoelectric plate is attached to the wall to measure the flag's flutter frequency. The results show that the performance of a flag with multiple strips outperforms that of the full flag for its lower pressure drop and higher heat dissipation effect. The performance of split flag is not linear with the strip number and the optimal way in our study is to split the full flag into 4 strips. The maximum thermal-hydraulic performance factor of the split flag is 1.91, which is 26% higher than that of the full flag. Besides, the split flag starts fluttering at a lower wind velocity. All these results demonstrate that the split strategy of a flag acting as a vortex generator is of great potential for improving the heat sink performance.
... It was determined that while the VGs were rotating in the same direction, the amplitude of Nu and friction factor were higher. Zheng et al. [2020] performed a 2D numerical analysis using FVM on turbulent flow filed of water-DWCNT-TiO2 hybrid nano-fluid with semicircular and triangular VGs. The semicircular VG showed a more promising result in terms of overall pressure drop and heat transfer performance. ...
Flexible vortex generators have recently gained attention in terms of their hydraulic and thermal effects in different applications. In the present study, a singular vortex generator as a flexible beam attached to a pin-fin is considered in an array of staggered pin-fins. A 2D model is developed from an already available microchannel heat-sink design that uses 15 cylindrical pin-fins in a staggered configuration from the literature. The laminar flow is coupled with the elastic solid domain. To solve the fluid-solid interaction equations, the arbitrary Lagrangian-Eulerian methodology is employed using a commercial software that utilizes Finite-element method. The numerical model is validated with respect to two procedures to ensure the safety of the method. The effect of moving vortex generator in the vicinity of the pin-fins is studied and the movement of the generated vortex at the tip of the beam through the flow and its effects on the main flow are investigated. A simple energy balance is at work to study the thermal performance of the design. In terms of pressure drop, an enhancement of near 4% is observed while the overall thermal efficiency of the system is found to be 3.6% improved compared to the heat-sink without vortex generator.
... Many examples can be found in the biochemical and biomedical as well as the food processing industries [1]. Zheng et al. [2] investigated the impact of a vortex generator shape on liquids and the heat transformation of hybrid nanofluids in a channel. D'Ippolito et al. [3] studied the resistance of open channel flow because of vegetation at the research scale. ...
The present paper deals with the advancement of non-Newtonian fluid containing some nanoparticles between two parallel plates. A novel fractional operator is used to model memory effects, and analytical solutions are obtained for temperature and velocity fields by the method of Laplace transform. Moreover, a parametric study is elaborated to show the impact of flow parameters and presented in graphical form. As a result, dual solutions are predicted for increasing values of fractional parameters for short and long times. Furthermore, by increasing nanoparticle concentration , the temperature can be raised along with decreasing velocity. A fractional approach can provide new insight for the analytical solutions which makes the interpretation of the results easier and enable the way of testing possible approximate solutions.
... There are several previous studies carried out using nanofluids with a vortex generator to determine their effect on the heat transfer process. Zheng et al. [22] investigated numerically the flow and heat transfer characteristics using water/DWCNT-TiO2 hybrid nanofluid, in a rectangular channel with semi-circular and triangular VGs. The results illustrated that heat transfer was enhanced by increasing and the volume fraction. ...
In this paper, a numerical simulation is performed to study the effect of two types of concave vortex generators (VGs), arranged as fish-tail locomotion in a rectangular channel. The heat transfer and fluid flow characteristics with and without VGs are examined over the Reynolds number range 200≤Re≤2200.The two proposed types of the VGs are selected based on the speed of the fish movement which is arranged in different distances between them (d/H=0.6, 1, 1.3). The results show that the use of VGs can significantly enhance the heat transfer rate, but also increases the friction factor. The heat transfer performance is enhanced by (4-21.1%) reaching the maximum value by using the first type of the VGs at (d/H=1.3) due to better mixing of secondary flow and the new arrangement of the VGs which lead to decreasing the friction factor with an easy flow of fluid.
... Shafee et al [34] concluded that Hartmann number ameliorates Bejan number in their work on water based HNF flow in a porous enclosure surrounded by different type of walls (two curved and two straight). Zheng et al [35] used FVM (finite volume method) to analyse HNF flow in rectangular channel with (four) vortex generators. Gul et al [36] applied HAM to analyse the heat transfer characteristics of the nanofluid flow in a disk-cone apparatus. ...
Despite numerous reports on the newly discovered hybrid nanofluid, little is known on the influence of increasing Reynolds number, stretching of lower, and upper diskson the dynamics of water
conveying graphene and silver between rotating disks when Lorentz force, Joule heating, suction, thermal radiation of thermal energy, and Cattaneo-Christov heat flux are highly significant. This report provides insight into such transport phenomenon with an emphasis on the increasing effects of Reynolds number, stretching of lower, and upper disks. Initially, leading equations of motion and energy are transmuted into a system of nonlinear ordinary differential equations with the aid of suitable (Von-Karman) similarity transmutations. Later, by enforcing shooting procedure (R-K 4th order based) to obtain the numerical solutions. Based on the analysis, it is worth concluding that increasing the Reynolds number improves the thermal field but reduces the tangential velocity. Entropy generation is an increasing property of stretching lower and upper disks but these are yardsticks for decreasing Bejan number.
... The researchers used different passive techniques to increase the heat transfer rate in different thermal systems. These techniques are usage of nanofluids as the working fluid [6][7][8], usage of porous materials [9,10], usage of vortex generators [11,12], and other techniques [13,14]. ...
An irreversibility analysis is arranged for the turbulent convective flow through the panel type radiator equipped with the vortex generators. Delta wing vortex generators are installed inside the system to disrupt the flow and enhance the heat transfer rate. However, vortex generator may affect the second law efficiency of the system, which should be investigated. The increase in the entropy production restricts the thermodynamic advantages of the vortex generators. The influences of several parameters, including the attack angle of vortex generator β, space between the back edge of vortex generator and hot surface of the panel, d, and Re number, Re, on the velocity and temperature characteristics, entropy production owing to viscous friction and heat transfer, and Be number are studied. The results attained by the present numerical investigation are validated with the data reported in the literature to ensure about the accuracy of the numerical solver. The outcomes revealed that the entropy production owing to viscous friction is increased with increasing the attack angel of vortex generators and space between the back edge of vortex generator and the hot surface of the panel. The larger values of entropy production owing to heat transfer are produced when the vortex generators are placed farther from the hot surface of the panel. Both entropy production owing to viscous friction and heat transfer increase with placing the vortex generators inside the panel. The substrate of high Be number grows along the panel length and occupies most of the panel at the exit section. By the way, the entropy production owing to viscous friction is dominate term at the entrance of the panel owing to the high velocity gradient of the developing flow regions.
... This process is done within the VTs without any moving part in their components. Accordingly, they have been used in different industrial applications such as the natural gas industry, water desalination system, and space crafts [8][9][10]. The energy separation in VTs is a classical phenomenon in the science of fluid mechanics. ...
In this work, a new configuration of the vortex tubes (VTs), called annular VTs, is proposed to improve the temperature separation performance. In the proposed configuration, a compartment has been added on the top of the tube wall that the separated hot outlet is repassed inside it over the hot tube. An axisymmetric swirl model of the Ranque-Hilsch VT (RHVT) and annular VTs is numerically simulated, and the thermo-hydraulic characteristics of them are compared for cold mass fractions ranging 0.2-0.8. The results illustrated that a small secondary circulation is created near the cold outlet of the RHVT that is not observed in the annular model. This secondary circulation is a destructive mechanism in VTs that results in more mixing and higher temperature in the cold outlet section. Analyzing the results indicates that using annular VT causes up to 12.51% increment of the hot outlet temperature compared to the RHVT model (which occurs at a mass fraction of 0.23). Also, up to 9.23% reduction of the cold outlet temperature is occurred (which occurs at a mass fraction of 0.37). These explanations prove the improvement of the annular VT compared to the conventional VTs.
... 3. Our validation was done using the enhanced wall treatment method. 4. Numerous papers have employed enhanced wall treatment method during their modeling process [42][43][44][45][46][47]. ...
In the current study, the turbulent forced convection heat transfer of Fe3O4/-CNT/water hybrid nanofluid (HNF) in a heat exchanger (HE) equipped with blade-shape turbulators is studied. The 3D governing equations have been solved numerically with SIMPLEC algorithm and solution domain by employing the control volume method (CVM). The impact of Reynolds number (Re), volume concentration of Fe3O4 nanoparticles (φM) and CNTs (φCNT) and blade-rod diameter (dr) on the performance features of HE are evaluated. The results showed that the PEC of HNF augments with the augmentation of Re and φM, while with intensifying dr, the PEC first rises and then declines. The outcomes showed that the highest PEC occurs at Re = 9000, φM = 0.9%, φCNT = 1.35% and dr = 15mm.
... There are various techniques for enhancing the heat transfer rate and thermal efficiency of these thermal systems, which also decrease the size of the heat exchangers. The following methods are popular in recent years because of simple installation and low costs: (1) using nanofluids as the working fluid [1,2], (2) using twisted tapes (TTs) [3][4][5][6], (3) conical rings [7,8], grooved surfaces [9], hollow cylinders [10], and (4) combined use of vortex generators and nanofluids [11][12][13]. ...
This numerical investigation aims to study the turbulent characteristics and thermal enhancement parameter of CuO–water nanofluids through heat exchangers enhanced with double V-cut twisted tapes. The twist ratio of the twisted tapes is 5.25, and the cut ratio (b/c) is varied from 0 (conventional twisted tape) to 1.8. The Reynolds number is in the range of 5000–15,000, and nanoparticles volume fraction is in the range of \(0 < \phi < 1.5\%\). The flow is fully turbulent, and (RNG) k − ϵ turbulent model is used for the numerical analysis. The results reveal that strong turbulent kinetic energy and additional vortex flow through the cuts of the modified twisted tapes are the main reason for better fluid mixing and heat transfer enhancement. The heat transfer enhances about 14.5% for the case of \(\phi = 1.5\%\). Furthermore, using double V-cut twisted tapes improves the Nusselt number of the nanofluid flow inside heat exchangers about 138% compared to conventional twisted tape without cuts. The maximum value of the thermal performance \(\left( {\eta = 1.99} \right)\) is achieved by using nanofluid with \(\phi = 1.5\%\) and b/c = 1.8 at Re = 5000.
... The result showed a 167% increase in thermal performance of plate-fin heat exchanger with combined use of VG and nanofluid. Zheng et al. [30] examined the effect of vortex generator shape on turbulent heat transfer and fluid flow of a hybrid nanofluid in a channel. The results show that the semicircular vortex generator has a higher average Nusselt number than a triangular vortex generator. ...
Enhancement of heat transfer in plate-fin heat exchangers can be obtained using vortex generators (VG). The three-dimensional laminar flow of water/Al2O3 nanofluid with different nanoparticle volume fractions in a channel with longitudinal vortex generators is numerically simulated. Two novel forms of modified delta winglet VG pairs (MDWP1, MDWP2) are introduced by adding and subtracting a part of the quadrant profile to the delta winglet VG profile. Simulation is carried out for the classic delta winglet pair (DWP) and MDWPs. Performance of heat transfer and pressure drop is compared as well as the overall performance analysis of channel is conducted for all three forms of VGs and two flow arrangement types, common flow up (CFU) and common flow down (CFD). Analytical expressions from the literature are used to check the validity of the model. Governing equations of laminar fluid flow and heat transfer are solved based on the finite-element method. The range of Reynolds number is from 100 to 500. Results show that in the range of the present study, using nanofluid increases about 20% of the heat transfer coefficient and 18% of pressure drop compared to pure water. As results confirm in all of the cases, the heat transfer coefficient increases using VG. The MDWP2 leads to the highest pressure drop and heat transfer between the three VGs types. It can produce up to 9% higher heat transfer coefficient in Re = 100 and 20% of higher pressure drop for CFD flow arrangement. The overall performance of the CFD arrangement is higher than CFU for the studied cases relatively. And the values of performance in a channel with DWP are greater than MDWP1 and MDWP2, which is due to the lower pressure drop of DWP.
... The flow divider (turbulator) has efficiently disturbed the boundary layers of the fluid flow resulting in the thermal performance enhancement. Zheng et al. [48] numerically investigated the low-dimensional heat transfer of a nanofluid turbulent flow of water-DWCNT-TiO2 inside a rectangular channel with two types of turbulators including triangular and semicircular shapes. They considered three different heights of turbulators to evaluate the effect of the heights on the channel heat transfer. ...
This article presents the effects of a circular disk obstacle with different angle ratios on heat transfer and pressure drop under a turbulent flow inside the tube with a constant temperature wall. Remarkable investigations have suggested the use of various obstacles for heat transfer enhancement in heat exchangers. The used geometry for almost all studies has been fixed obstacles. However, the use of the rotary obstacle is an innovative issue to the author’s best knowledge. The obstacle rotation influences heat transfer rate through the effective displacement of the fluid particles. Thus, this investigation studies the effect of disk obstacle rotation from 50 to 200 rpm at different angle ratios and pitch ratios 1 and 2 on heat transfer and pressure drop in shell and tube heat exchanger of water–air type in the Reynolds number between 10,000 and 25,000. The results showed that rotating obstacles have less pressure drop than that of the fixed obstacle under similar shape and configuration. Compared to the smooth pipe, the Nusselt number, friction coefficient, and thermal performance coefficient increased by 300%, 69.38%, and 131%, respectively. The maximum heat performance coefficient 1.62 times relative to the fixed obstacle in similar condition was recorded.
Nanofluids and hybrid nanofluids enhance the transfer of heat with low nanoparticle concentration. Tri-hybrid nanofluids combine different nanoparticles (NPs) to further increase the performance of base fluids. Tri-hybrid nanofluids have significant uses in several industries, including electronic cooling, heat transport, biomedical engineering as well as energy storage systems. This study investigates the thermal performance of tri-hybrid nanofluid in the existence of a magnetic field and porous saturated space along with copper (Cu), aluminium oxide (Al 2 O 3 ), and titanium dioxide (TiO 2 ) NPs dispersed in base fluid, i.e. water (H 2 O) flowing through a vertical channel by convection. The resultant partial differential equations based on Atangana–Baleanu time-fractional derivative (having non-singular and non-local kernel) are solved using the Laplace transform along with the appropriate physical conditions. The Stehfest as well as Tzou’s numerical approaches are then utilized to compute the Laplace inverse, to check the validity of obtained solutions and to get the graphical representations of, concentration, energy, and velocity fields. The results show that tri-hybrid nanofluids have advanced thermal as well as momentum characteristics compared to nanofluids and hybrid nanofluids.
In this paper, we aim at the simulation of setup for vortex generation and measurement. This project will lead to designing the experimental setup to create vortices and development of heat flow sensors. The working fluid for the vortex generator is hybrid nanofluid such as Iron (III) Oxide-MWCNT and propanol. The usage of these hybrid fluids was considered due to their better physical and chemical properties compared to water and other conventional fluids. Ansys Fluent was used to simulate the experiment. Viscosity of the fluid increases for both hybrid nanofluids, from inlet to outlet by a magnitude of 10 times (for Fe3O4 + MWCNT: 5.3 × 10−5 Pa.s to 6.3 × 10−4 Pa.s; for Al2O3 + MWCNT: 7.5 × 10−5 Pa.s to 6.5 × 10−4 Pa.s), for laminar flow (Reynolds number = 400). Vortex generation increases the viscosity of the hybrid mixture but not water (for water, it stays constant across the channel at 4.9 × 10−4 Pa.s). Vortex induced viscosity is seen in hybrid mixtures. Strain thinning due to vortex formation is not observed, therefore the behavior of the mixtures is along the lines of Newtonian fluids.
According to a remarkable result, the polarization diffusion coefficient of drugs, such as those that slow down and ease the body, may be determined based on the rise in magnetism that follows. This research examines how a magnetic field impacts the Casson-type flow of a viscous, incompressible hybrid nanofluid that naturally flows across two parallel plates. Copper (Cu) and aluminum-oxide (Al 2 O[Formula: see text] are the two nanoparticles and their physical properties are intended to be the foundation fluids, together with water and sodium alginate as based fluids. The revised fractional model is investigated using the Laplace transformation using the most current and updated definition of the fractional-order derivative with memory effect, i.e. Prabhakar fractional derivative. The impacts of various constraints on distinct nanoparticles are investigated and visually depicted. As a result, we have concluded that a drop in volumetric percentage reduces fluid velocity. The water-based hybrid nanofluid (HNF) has a more significant influence on the temperature and momentum profile than the sodium alginate-based HNF due to the physical appearances of the investigated nanoparticles. The Casson fluid parameter augmentation also regulates the velocity profile by decreasing the velocity field.
Convective heat transfer plays an important role in the development of a high-performance battery cell. Electric vehicles carry a large amount of the battery cells to reach a longer range of endurance mileage. Thermal diffusion around the battery cells can be considered as obstacles to improve the convective heat transfer coefficient. In this paper, a novel agitator taking advantage of strong vortices is designed to disrupt the thermal boundary layer around the battery cells, thereby improving the fluid mixing for enhanced convective heat transfer. A fluid–structure interaction algorithm is developed to simulate the convective heat transfer rate at various flapping motion. Under the comparison with clean channel, the vortex-induced vibration by the agitated beam can increase the average Nusselt number by 119.59%. This research can be applied to optimize the thermal-structure design inside the electric vehicle battery.
The functional effects of medications, such as those that slow down and calm the body, have been investigated for the polarized diffusion coefficient based on the subsequent increase through magnetism. This study examines generalized Mittag-Lefer kernel-based fractional derivatives in MHD Brinkman-type fluids under bioconvection that contain hybrid titanium dioxide (TiO 2) and silver (Ag) nanoparticles with water (H 2 O) and sodium alginate (NaC 6 H 7 O 6) as the base fluids. Atangana-Baleanu (AB) and Caputo-Fabrizio (CF) fractional derivatives, which are two contemporary definitions of fractional-order derivatives with a memory effect, were used to explore the modified fractional model utilizing the Laplace transformation and certain numerical algorithms. The impacts of restrictions on various nanoparticles were investigated and graphically displayed. We observed that the volumetric fraction improvement controls the fluid velocity by slowing it down. The water-based hybrid nanofluid has a greater influence on the temperature and momentum fields than the sodium alginate-based hybrid nanofluid due to the physical characteristics of the explored nanoparticles and base fluids. Additionally, the memory effect causes a higher substantial value for the AB-fractional derivative of the velocity profile than the CF-fractional derivative.
The functional effects of medications, such as those that slow down and calm the body, have been investigated for the polarized diffusion coefficient based on the subsequent increase through magnetism. This study examines generalized Mittag-Lefer kernel-based fractional derivatives in MHD Brinkman-type fluids under bioconvection that contain hybrid titanium dioxide (TiO 2) and silver (Ag) nanoparticles with water (H 2 O) and sodium alginate (NaC 6 H 7 O 6) as the base fluids. Atangana-Baleanu (AB) and Caputo-Fabrizio (CF) fractional derivatives, which are two contemporary definitions of fractional-order derivatives with a memory effect, were used to explore the modified fractional model utilizing the Laplace transformation and certain numerical algorithms. The impacts of restrictions on various nanoparticles were investigated and graphically displayed. We observed that the volumetric fraction improvement controls the fluid velocity by slowing it down. The water-based hybrid nanofluid has a greater influence on the temperature and momentum fields than the sodium alginate-based hybrid nanofluid due to the physical characteristics of the explored nanoparticles and base fluids. Additionally, the memory effect causes a higher substantial value for the AB-fractional derivative of the velocity profile than the CF-fractional derivative. CITATION Raza A, Nigar N, Khan U, Elattar S, Eldin SM and Abed AM (2023), Comparative investigation of fractional bioconvection and magnetohydrodynamic flow induced by hybrid nanofluids through a channel.
This paper introduces a novel theoretical model of ternary nanoparticles for the improvement of heat transmission. Ternary nanoparticles in a heat conductor are shown in this model. Ternary nanoparticles consist of three types of nanoparticles with different physical properties, and they are suspended in a base fluid. Analytical solutions for the temperature and velocity fields are found by using the Laplace transform approach and are modeled by using a novel fractional operator. As a result, the ternary nanoparticles are identified, and an improved heat transfer feature is observed. Further experimental research on ternary nanoparticles is being carried out in anticipation of a faster rate of heat transmission. According to the graphed data, ternary nanoparticles have greater thermal conductivity than that of hybrid nanoparticles. Moreover, the fractional approach based on the Fourier law is a more reliable and efficient way of modeling the heat transfer problem than the artificial approach. The researchers were driven to create a concept of existing nanoparticles in order to boost heat transfer, since there is a strong demand in the industry for a cooling agent with improved heat transfer capabilities.
The thermal-hydraulic performance of a ribbed corrugated channel in which a hybrid nanofluid flows was numerically investigated in the wide range of change in the Reynolds number of the fluid flow 5000–25,000 with the use of the k–ε model of turbulence. Rectangular oblique ribs different in geometry were considered, and a CuO/MgO–water nanofluid was used as a working fluid. It was established that the corrugations and the oblique ribs in such a channel aid in increasing the heat transfer in it, and the CuO/MgO particles in the base fluid improve its thermophysical properties and, hence, the thermal performance of the system.
Nanofluids are an engineered suspension of nanoparticles in a standard working fluid that considerably enhances the characteristics of heat transfer (H.T) over the source fluid. The construction of the heat exchanger (H.E) is determined not only by the architectural geometry of the design or other configurations, but also by the properties of the working fluid. In recent years, the traditional working fluid has been replaced by a space for improvement by a nanomaterial-enriched nanofluid. Nanoparticles such as Al2O3, CuO, TiO2, MWCNT and ZnO accelerated the H.T process by enhancing the thermal conductivity of the working fluids. This means that nanofluid can behave more like a one-phase system than a two-phase system, depending on the size and surface properties of the nanoparticles. Furthermore, because of their versatile properties and small size, nanofluids should be ideal for industrial applications. The prime purpose of this chapter is to summarize the most recent research articles on the performance of nanofluids in various heat exchangers. Various types of H.Es are also discussed, as well as the challenges of design optimization for increased effectiveness.
Recent studies in the field of thermal engineering revealed that employing nanofluid as a working fluid in a specific channel, considering both turbulators and magnetic field effect is scarce. Studies on the convective heat transfer performance of the thermal systems focus mostly on the effect of using either nanofluid as a new fluid, magnetic field, or turbulators. This review highlights the single and combined effects of these parameters on the heat transfer enhancement of such systems. Nanofluid type, its volume fraction, channel and turbulator geometry, magnetic field type, and flow regime were considered as the base parameters while the enhancement in heat transfer is evaluated. From a state-of-the-art review, it was noticed that most studies reveal that increasing the volume fraction of nanofluid, magnetic field strength, and Reynolds number can attain an upsurge in the heat transfer in a specific channel. Nevertheless, drawbacks are poorly discussed in the open literature. Regarding the turbulator geometry, which actually limits the magnetohydrodynamic and thermal boundary layer development, its complexity boosts also the convective heat transfer. The maximum heat transfer enhancement was noticed for higher nanoparticle volume fractions, higher magnetic field strengths, and complex geometries in channel flow. The highest heat transfer improvement was obtained for the MWCNT/H2O nanofluid (i.e., between 70% and 190%). With the effect of magnetic field intensity of Ha = 30 applied to the Cu/H2O nanofluid flow, a thermal recovery of 76% was achieved. Concluding, this comprehensive review can be beneficial to researchers working in the field of flow and heat transfer applications with the use of nanofluid, turbulator, and magnetic field together.
The present work deals with the numerical analysis of thermohydraulic performance of based nanofluid flow through straight slot rib rectangular channel. The integration of the artificial roughness on the heated surface and use of the nanofluid as a heat transferring medium makes the present system efficient. Important parameters such as Reynolds number () is selected in the range of 5000–8000, relative slot rib height () in the range of 0.060–0.084 and other parameters have been fixed are spanwise pitch () 4.07, streamwise pitch () is 7.6, nanoparticle concentration () is 3% and nanoparticle diameter () of 40 nm. The analysis resulted in the maximum value of Nusselt number () and friction factor () at value of Relative height ratio () of 0.084 and 0.06, respectively. It is found that the value of relative slot rib height 0.084 delivers the highest thermohydraulic performance () in comparison to other values of geometric parameters.
In this study, flow and heat transfer characteristics of binary hybrid nanofluid (CuO / MgO-water) through new configuration channel, namely: the curved-corrugated channel, are evaluated numerically using the multi-phase mixture model. The binary hybrid nanofluid is experimentally prepared with average diameters of 40 nm and three volume fractions of nanoparticles of 1%,3%, and 5%. Measured thermophysical properties are employed to simulate the complex flow within the tested configurations of channel with presence of E-shaped baffles. Various geometric parameters such as gap ratio (GR = 0.2,0.3,0.4, and 0.5), blockage ratio (BR = 0.2,0.25,0.3, and 0.35), and pitch angle (β = 10°, 12.5°, and 15°) at different Reynolds number (8000–28,000) and volume fraction (φ) of CuO / MgO particles (0–5%) are considered to serve the purpose. The findings uncover that the binary hybrid nanofluid improves the thermophysical properties of the base fluid and thereby boost the thermal performance of the system. It is found that the thermal-hydraulic performance (THPF) of binary hybrid nanofluid enhances with increasing volume fraction, and this enhancement is close to 38% when Re = 28,000 and φ = 0.05. Regards the geometric parameters, THPF enhances by increasing the blockage ratio and decreasing the pitch angle while recording the best improvement at the particular gap ratio, i.e. 0.3.
An attempt is made to enhance the thermal hydrodynamic performance of a solar channel by using vortex generators including attached fins and detached bars. Hydrogen gas is used as a working fluid under turbulent flow conditions.
The computational fluid dynamics method is used to achieve the investigations. Governing equations among fluid and solid sections are determined and solved by the computational finite volume method. The hydrodynamic characteristics, dynamic pressure, turbulent kinetic energy, turbulent viscosity, Nusselt number, skin friction, and the thermal enhancement factor (TEF) are investigated for a range of Reynolds number (Re) from 5000 to 20,000. The obtained results revealed that the TEF values are important (TEF > 1) for all Re values under investigation. The TEF values are between 1.2 and 3.5. An increase in the TEF values was observed with increased Reynolds number, where the maximum value of TEF of about 3.5 was achieved at Re = 20,000. At this value of Re, the normalized heat transfer value (Nu/Nu0) is the highest, while the normalized friction values (f/f0) are the lowest. This demonstrates the usefulness of the suggested vortex generators combined with the fluid (H2) for the successful thermal and dynamic performance within the smooth channels.
In the present study, numerical simulations have been carried out on thermal characteristics and second-law analysis of turbulent Cu–H2O nanofluid flow with the nanoparticle volume fraction of \(0 < \phi < 1.5\%\) inside heat exchangers fitted by transverse-cut twisted tapes (TCTTs) with alternate axis. The transverse-cut ratios are in the range of 0.7 < b/c < 0.9 and 2 < s/c < 2.5, and the Reynolds number is varied between 5000 and 15,000. The impacts of the design variables on the turbulent kinetic energy, temperature distribution, thermal and frictional entropy generations and Bejan number have been evaluated. The simulations show that the TCTTs with b/c = 0.7 generate higher turbulent kinetic energy compared to the b/c = 0.9 due to higher swirl generation and flow disturbance. The additional recirculating flow produced near the alternate edges is another main physical factor for heat transfer augmentation. It is found that raising the nanoparticles volume concentration reduces the thermal entropy generation which is attributed to the thermal conductivity enhancement of nanofluids. Besides, raising the nanoparticles volume concentration from 0 to 1.5% reduces the \({{N}_{\text{g,thermal}}}\) by 23%.
In this paper, the effect of different channel spacing in spiral heat exchanger filled with Cu–ZnO–water hybrid nanofluid was investigated to find the optimum thermal–hydraulic performance. The hot water flow enters into the test section from central aperture of heat exchanger, and the cold hybrid nanofluid flow enters into the test section from the outer aperture of the heat exchanger. The effects of different flow velocities, nanoparticles φ and channel spacing values have been analyzed. Results have been presented on Nusselt number, outlet temperature, pressure drop and PEC. According to the obtained results, channel spacing decrease in constant flow velocity values is more effective than volume fraction increase on outlet temperature improvement. Also, an increase in inlet flow velocity leads to lower heat transfer between cold and hot channels, but the growth of volume fraction can improve the thermal efficiency of the heat exchanger at high velocities. On the other hand, the reduction in channel spacing leads to more pressure drop penalty. Especially for the hot water flow, this behavior reduces the hydraulic performance of heat exchanger. The less the channel spacing, the more the pressure drop. The highest average Nusselt number occurs at a velocity of 0.45 (m s−1) and φ = 4% at a channel spacing of 35 mm. The maximum value of the pressure drop occurs at b = 2.5–5 mm. Besides considering the PEC value, 2% volume fraction is recommended for the spiral heat exchanger.
In this paper, non-Fourier heat conduction in a cylinder with non-homogeneous boundary conditions is analytically studied. A superposition approach combining with the solution structure theorems is used to get a solution for equation of hyperbolic heat conduction. In this solution, a complex origin problem is divided into, different, easier subproblems which can actually be integrated to take the solution of the first problem. The first problem is split into three sub-problems by setting the term of heat generation, the initial conditions, and the boundary condition with specified value in each sub-problem. This method provides a precise and convenient solution to the equation of non-Fourier heat conduction. The results show that at low times (t = 0.1) up to about r = 0.4, the contribution of T1 and T3 dominate compared to T2 contributing little to the overall temperature. But at r > 0.4, all three temperature components will have the same role and less impact on the overall temperature (T).
In this study, effects of various geometrical parameters of a new winglet longitudinal vortex generator (LVG) on heat transfer and flow characteristics in a rectangular channel were investigated by a numerical method, and the influence of various parameters was analyzed. A comparative study of effects of elliptical pole parameters, the thickness, the length, the height, the attack angle, the transverse pitch and the longitudinal pitch of LVGs on heat transfer and pressure loss performance was conducted. The results showed that the intensity of heat transfer could be greatly increased by the increase of the length, the height, the attack angle and the transverse pitch of LVGs, accompanied with an increase of pressure drop. The Nusselt number decreased by increasing the longitudinal pitch of LVGs. The short axis and major axis of the elliptical poles and the thickness of LVGs had a small influence on the average heat transfer coefficient and average friction factor at the present condition. The design parameters of this configuration were optimized by the Taguchi method. Sixteen kinds of models were made by compounding levels on each factor, and heat transfer and flow characteristics of each model were analyzed. The results allowed us to quantitatively estimate the various parameters affecting heat transfer performance, and the main factors for optimal design of a rectangular channel with LVGs were selected. The optimal condition was also acquired by two analytical results.
In the present work, the effect of the angle of a triangular vortex generator on the heat transfer of a flat plate is investigated. Incompressible three-dimensional fluid flows in a channel with constant temperature boundary condition. The results showed that the Nusselt number increases and the pressure decreases with the Reynolds number. It is demonstrated that the increase in the angle from 30° to 90° has a significant effect on the Nusselt number. The pressure drop remains constant at a 60° angle with increasing Reynolds number. The results revealed that the longitudinal vortices that have an important effect on the heat transfer become stronger at larger angles of the vortex generator. © 2018 International Information and Engineering Technology Association. All Rights Reserved.
Perforated fins effects on the heat transfer rate of a circular tube are examined experimentally. An experimental system is set up through the wind tunnel and equipped with necessary measurement tools. Hot water passes through the finned tube and heat transfers to the fin-side air created using the wind tunnel with different velocities. Two fin sets of identical weight are installed on a circular tube with different outer diameters of 22 and 26 mm. The experiments are conducted at two different mass flow rates of the hot water and six Reynolds number of external air flow. Considering the four finned tubes and one no finned tube, a total of 60 tests are conducted. Results showed that with increasing the internal or external flow rates, the effect of larger cross-sectional area is greater. By opening holes on the fins, in addition to weight loss, the maximum heat transfer rate for perforated fins increases by 8.78% and 9.23% respectively for mass flow rates of 0.05 and 0.1 kg/s at low external Reynolds number. While, at high external Reynolds number, the holes reduces heat transfer by 8.4% and 10.6% for mass flow rates of 0.05 and 0.1 kg/s, respectively.
In this study, a thermal model for estimating the efficiency of a basin solar still with an external reflector was introduced using the energy balance equations of different parts of the solar still. Then, in order to verify the precision and accuracy of this model, a basin solar still with an external reflector was constructed and some experiments were performed. The hourly temperature values for different places of the still and amount of distilled water were calculated using the thermal model and compared with experimental measurements. Comparisons show that the thermal model of the still is in good agreement with the experimental results. Therefore, it can be concluded that the introduced thermal model can be used reliably to estimate the amount of distilled water and efficiency of the basin solar still with an external reflector. Results also revealed that the efficiency of the solar still is low in the early hours, while it was enhanced 44% in the afternoon. Furthermore, it was concluded that the accumulated distilled water is 4600 mL/day and 4300 mL/day for theoretical and experimental examinations, respectively.
In the present study, the flow and heat transfer of CuO-water nanofluid in different solid concentrations (1–4 vol%) in a tube have been simulated by using the single- and two-phase (mixture) models. The simulations have been conducted under the turbulent flow regime in different Reynolds numbers ranging from 3000 to 36,000. The effects of using CuO-water nanofluid on the Nusselt number, friction factor, and performance evaluation criterion have been investigated. It is found that employing the two-phase mixture model leads to having closer results in reality compared to the single-phase model. The results revealed that the maximum performance efficiency coefficient in the tube with one twisted tape is 2.18 (for the two-phase model, Re = 36,000 and φ = 4%), while for a tube with two twisted tapes under the same conditions, it is 2.04. Thus, the use of one twisted tape is more favorable from the thermal-fluid dynamics viewpoint.
This study simulated the forced convective heat transfer of water/alumina nanofluid in a rectangular microchannel. Three techniques were used to enhance heat transfer. First, three top fluid injection points and three bottom ones (six injections in total) were added to the base microchannel. Different fluid injection layouts and their effect on enhancing the thermal performance of the microchannel were then investigated. Results supported the substantial effect of fluid injection layout on heat transfer as the mean Nusselt number was increased by a maximum of 25% (best layout) in high Reynolds numbers. The second technique involved adding of nanofluid to the base fluid. Results showed that adding nanofluid to the base microchannel increased the Nusselt number by a maximum of 3.5%. In the third technique, the fluid injection was added to a microchannel containing nanofluid. Results showed that injection in the presence of a nanofluid improved the Nusselt number by 28%. All three techniques entailed both a positive effect (increased heat transfer) and a negative effect (increased pressure drop). In the most effective technique, the pressure drop was 40% higher than the base microchannel at the point with maximum heat transfer.
This work explores the turbulent thermal-hydraulic performance in circular heat exchanger tubes with multiple rectangular winglet vortex generators. Numerical simulations demonstrate that multi-longitudinal vortices are induced, which enhances fluid mixing in the tubes. The effects of geometric parameters including the circumferential number of rectangular winglets (N = 4, 6, 8), height ratio (HR = 0.05, 0.1, 0.2), and pitch ratio (PR = 1.57, 3.14, 4.71), are examined experimentally. The results demonstrate that both the friction factor and Nusselt number increase with the height ratio and the number of rectangular winglets due to the better fluid mixing performance caused by multi-longitudinal vortices with higher turbulent kinetic energy. For the considered Reynolds numbers, the friction factor and Nusselt number ratios are in the range of 1.46–11.63 and 1.15–2.32, respectively. An increase in the number of rectangular winglets improves the thermal enhancement factor (TEF) for HR = 0.05, while the opposite trend is found for the other cases. The maximum TEF is up to 1.27. Moreover, correlations for the friction factor and Nusselt number are derived based on the experimental results for practical applications.
The energetic analysis of an air handling unit (AHU) combined with an enthalpy air-to-air heat exchanger has been studied to improve the first law thermodynamic efficiency. The energy balance equations for enthalpy air-to-air heat exchanger, conditioned space, heating coil, cooling coil and mixing box have been performed and solved based on a program developed in Engineering Equation Solver. The results showed that using an enthalpy air-to-air heat exchanger leads to energy recovery which in turn decreased the total required AHU power. The effect of using an enthalpy air-to-air heat exchanger on recovered energy in hot and humid ambient is more than the cold and dry one. Using the enthalpy air-to-air heat exchanger, the cooling coil load decreases by 28.27%, which in turn increases the first law efficiency by 32.8%.
In this study, a new design for energy recovery from the return air has been introduced to improve the air handling unit (AHU) performance through the energetic analysis. The main objective is defined as the reduction in cooling and heating coils energy demand. In the novel AHU, the coldness from the exhaust air is transferred to the fresh air through the primary heat exchanger to reduce the cooling coil energy usage, while in the secondary heat exchanger, the warmness from the return air is recovered to the outlet cold air of the cooling coil to reduce the heating coil energy usage. Results showed that using air-to-air heat exchanger in hot and dry climate regions, the total energy consumption decreased up to 26.38%, which in turn increased the first law efficiency up to 35.84%, while in hot and humid climate these figures are 13.11% and 10.57%, respectively. It is concluded that the effect of using the air-to-air heat exchangers in hot and dry climate has priority over the hot and humid one.
Preparation, stability of Nano-fluid and the thermal conductivity of Graphene oxide/Water Nano-fluid with the aim of improving the thermal properties of water were experimentally studied. FESEM and XRD tests were used for characterization of nano-particles. After getting assured of the structure of nano-particles, a two-step method was applied to produce Graphene oxide/Water Nano-fluid. Optimal pH, DLS and TEM tests were used to determine the stability. The mass fraction range of the Nano-fluid in this study was 0–1.5%, and the thermal conductivity was measured in the temperature range of 20–60 °C according to ASTM D2717–95 standard. The results indicate that the Nano-fluid has the highest stability at optimum pH (pH = 8). The results of TEM and DLS tests show the sheet structure of the nano-particles and their Nanoscale dimensions in the base fluid, respectively. The thermal conductivity of the Nano-fluid in the study range indicates a significant increase and its maximum increase is 48.1%. Using the curve fitting method, a new correlational with high accuracy has been proposed. Finally, according to the results obtained, it can be said that the Nano-fluid, with respect to its thermal properties in the practical systems, is an appropriate alternative to water-based fluid.
This study investigated the convective heat transfer and pressure drop of non-Newtonian nanoporous graphene nanofluids. The nanoporous graphene nanofluids were prepared using different concentrations of nanoparticles (i.e. 0.05, 0.1, and 0.2 wt%) in an aqueous solution of carboxymethyl cellulose, and the thermophysical and rheological properties were evaluated accordingly. Four types of circular perforated baffles with different hole numbers were designed and manufactured. The Nusselt number, friction factor, and thermal performance factor (TPF) were calculated for the nanofluid and the base fluid flows by installing the baffles and were compared to those of the plain annular tube. The measurements showed that adding 0.2 wt% nanoporous graphene to the base solution led to enhancements of 12.4 and 39.4% in the thermal conductivity and the average heat transfer coefficient, respectively. The results indicated that by simultaneously using non-Newtonian nanoporous graphene nanofluid and perforated circular baffles, the average TPF value could be enhanced by 29% in the studied turbulence regime. These significant conclusions can be exploited to design highly efficient thermal systems possessing much better thermal efficiency.
Convection heat transfer in cavities has attracted much attention from researchers. Many kinds of nanofluids have exhibited non-Newtonian behavior and been employed as heat transfer fluids in cavities. In a non-Newtonian fluid, shear stress and strain do not have a linear relationship. Such fluids do not follow Newton’s law of shear stress. As a result, researchers have used such models as the power-law or Bingham to formulate the behavior of non-Newtonian fluids and provide a numerical solution. In this study, first the non-Newtonian nanofluids were summarized. And then two well-known models, namely the power-law and Bingham models, are introduced, which was followed by empirical studies in non-Newtonian fluids or nanofluids. Then a summary of studies on nanofluids and non-Newtonian fluids inside different types of cavities was provided. Moreover, some tables are presented summarizing numerical studies into cavities containing nanofluids or non-Newtonian fluids and their significant findings.
This paper conducts a new investigation of air purification with total heat recovery based on nanofluids for the first time to realize the synergistic application of nanofluids to the heat and mass transfer as well as the photocatalysis and sterilization fields. To explore the feasibility of the new application, the stable TiO2 nanofluids were obtained by a post-treated optimized preparation method. Then the experimental device is built to investigate the formaldehyde and total volatile organic compounds (TVOC) purification as well as sterilization. At last, the heat recovery characteristics of nanofluids are indirectly investigated by testing the gas-liquid bubbling heat transfer behaviour. The results show the post-treated method can improve the dispersion stability of nanofluids. The nanofluid system has efficient effects on air purification and sterilization for both fungi and bacteria. The nanofluids have higher gas-liquid bubbling heat transfer performance than water which increased as the particle loading.
Nano-fluids are produced by combining one or more nano-particles in a base-fluid. Nano-fluids, especially hybrid nano-fluids, have better thermal conductivities than simple liquids. The results of various articles demonstrated that various parameters such as nano-particles size, their volume fraction, temperature, aspect ratio, base-fluid, nano inclusions, additive, and pH affect nano-fluid thermal conductivity. In this paper, the effect of these parameters is reviewed by considering experimental works performed on thermal conductivity. Since thermal conductivity is measured by researchers experimentally, it is also important for researchers to understand the effect of nano-particles on humans and the environment. Thus, in this article, published articles in this field are reviewed and the effect of nano-particles on human and environment are investigated. The results of these articles indicated that nano-particles can endanger human health and can have irreversible effects on human health. The nano-particles also have a devastating effect on the environment and can affect the water, soil, and animals.
In this work, a review on single-phase convective heat transfer enhancement based on multi-longitudinal vortices is carried out. Theoretical investigations on convective heat transfer optimization from different principles such as entropy generation minimization principle, field synergy principle, entransy dissipation extremum principle, power consumption minimization principle, and exergy destruction minimization principle for the better trade-off between heat transfer augmentation and flow resistance reduction are firstly evaluated. It is found that the optimal flow fields are mainly characterized by multi-longitudinal vortices, implying that heat transfer enhancement techniques which can generate the flow patterns similar to the optimal flow fields may also enjoy the satisfactory balance between heat transfer enhancement and flow resistance reduction. Then, various techniques such as artificial roughness, special-shaped tubes, multiple swirl devices, and longitudinal vortex generators that can construct the flow pattern of multi-longitudinal vortices are summarized. Results indicate that most of the techniques show excellent thermal-hydraulic performance, but some techniques still suffer from high flow resistance. Based on the discussion, some new perspectives on the existing research gaps, challenging, and future research directions have been provided for the development of enhanced heat transfer techniques by generating multi-longitudinal vortices in heat exchanger tubes.
Thermal performance and pressure drop of TiO2-H2O nanofluids in double-tube heat exchangers are investigated. The influence of the thermal fluid (water) volume flow rates (qv = 1–5 L/min), nanoparticle mass frictions (ω = 0.0%, 0.1%, 0.3% and 0.5%), nanofluids locations (shell-side and tube-side), Reynolds numbers of nanofluids (Re = 3000–12000), and the structures of inner tubes (smooth tube and corrugated tube) is analyzed. Results indicate that nanofluids (ω = 0.1%, 0.3% and 0.5%) can improve the heat transfer rate by 10.8%, 13.4% and 14.8% at best compared with deionized water respectively, and the number of transfer units (NTU) and effectiveness are all improved. The pressure drop can be increased by 51.9% (tube-side) and 40.7% (shell-side) at best under the condition of using both nanofluids and corrugated inner tube. When the nanofluids flow in the shell-side of the corrugated double-tube heat exchanger, the comprehensive performance of nanofluids-side is better than that of the smooth double-tube heat exchanger.
A numerical investigation is conducted by implementing a two-phase model based on the mixture theory with the aim of assessing the attributes associated with the thermohydraulic performance of the Cu–water nanofluid through a square channel equipped by the 90° V-shaped ribs. The ribs are attached on the top and bottom walls of the channel with different rib heights and rib pitches. It is observed that the average heat transfer coefficient significantly enhances with the volume fraction increment such that it enhances around 22.7% with increasing the volume fraction from 1 to 2% at rib pitch of 100 mm and rib height of 2.5 mm. The presence of the ribs considerably intensifies the flow mixing and disrupts the thermal boundary layer by means of generating the four counter-rotating vortices. In addition, employing the ribs with greater heights as well as smaller pitches augments the heat transfer coefficient as well as Nusselt number, such that the Nusselt number increases about 28.3% when the rib height increases from 2.5 to 7.5 mm in the condition in which the rib pitch is 50 mm. The Figure of Merit (FoM), which shows the fraction of the convective heat transfer coefficient ratio to the pumping power ratio for the case of using the nanofluid compared to the water, is much higher than 1, which demonstrates the benefit of employing the nanofluid rather than the water. Furthermore, increasing the volume fraction results in a greater FoM, which manifests the greater merit of using the nanofluid at higher concentrations.
The present study aims at enhancing the thermal performance of SAE 50 engine oil by adding zinc oxide nanoparticles. The investigations are performed in the thermal range of 25 to 55 °C and at the volume fractions of 0.125 to 1.5%. In this regard, first, the characterization of nanoparticles was performed to examine their surface and atomic structure. Moreover, following the manufacture of the nano-lubricant, its stability was investigated by the DLS test. After ensuring the results of nano-lubricant stability, different samples were prepared according to the variations in volume fraction, followed by the experimental measurement of the thermal conductivity of nano-lubricant. The obtained results revealed an ascending trend in thermal conductivity by increasing temperature and concentration. The maximum thermal conductivity enhancement was 8.74%. Based on the experimental results, a sharply precise relation was proposed to predict the ratio of nano-lubricant thermal conductivity to that of the tested base fluid.
In the present study, turbulent flow and heat transfer inside a three-dimensional wavy microchannel with different wavelengths have been numerically simulated. The main purpose of this study is to investigate the effects of changing the wavelength of the sinusoidal microchannel and CuO nanoparticle concentration on flow and heat transfer properties. For this reason, flow is simulated at Reynolds numbers of 3000, 4500, 6000, and 7500 with volume fractions of 0, 1.5, and 3% in three different geometries and the effects of each parameter have been investigated. Validation of the results showed there is an excellent agreement between the presented results with the previous studies. The average Nusselt number, pressure loss ratio, performance evaluation criterion, and local Nusselt number have been presented. Moreover, the distribution of the static temperature contour has been presented. In the flow with lower Reynolds numbers, the Nusselt number is not changed significantly; however, in flow with Reynolds number of 7500, the Nusselt number is increased. The performance evaluation criterion has the highest value in nanofluid flow with the volume fraction of 3%, indicating the effects of heat transfer with pressure drop caused by nanoparticles, and from engineering and economic perspectives, using nanoparticles in the wavy microchannel is recommended.
This research aims to study the thermal and hydraulic attributes as well as energy efficiency of a new ecofriendly nanofluid including functionalized graphene nanoplatelets in a mini heat sink with three different pin fins. The circular, triangular and drop-shaped pin fins are investigated and compared with each other. The effects of nanoparticle fraction and flow velocity on the thermal resistance, temperature uniformity, convective heat transfer coefficient, maximum surface temperature, average surface temperature, pressure loss and pumping power are assessed. Increasing the concentration or velocity reduces the temperature on the heated wall, and also improves the temperature distribution uniformity. At both constant velocity and invariant pumping power, the heat sink fitted with the circular pin fins leads to the best performance while that equipped with the triangular pin fins results in the worst efficiency. In addition, the Figure of Merit (FoM) is greater than 1 for all conditions, which proves that the nanoparticle suspension possesses a greater merit to be employed as the coolant in the heat sinks compared to the base fluid.
Purpose
This study aims to simulate the flow and heat transfer through an air handling unit to reduce its energy consumption by a novel creative idea of using an air-to-air heat exchanger.
Design/methodology/approach
To do this, both first and second laws of thermodynamics energy and exergy balance equations were solved numerically by an appropriate developed computer code.
Findings
Using the air-to-air heat exchanger in dry conditions decreases the cooling coil load by 0.9 per cent, whereas the reduction for humid conditions is 27 per cent. Similarly, using air-to-air heat exchanger leads to an increase in the first law of efficiency in dry and humid conditions by 0.9 per cent and 36.8 per cent, respectively.
Originality/value
The second law of efficiency increases by 1.55 per cent and 2.77 per cent in dry and humid conditions, respectively. In other words, the effect of using an air-to-air heat exchanger in humid conditions is more than that in dry conditions.
The advantages of both the passive and active heat and mass transfer enhancement techniques are used. A beam (rigid or flexible) as vortex generator (VG) is placed downstream of a cylindrical obstacle on the lower wall of a microchannel. The governing equations are solved using ALE approach. The elastic beam oscillates due to the forces exerted by the periodic flow behind the obstacle on it leading to the formation and separation of periodic vortices from the tip of the beam. These vortices disrupt the thermal boundary layer and prevent it from re-growing and hence increase the heat transfer rate dramatically. The total Nu number increases 18.46%, the Darcy friction factor experiences a decrease of 42.33%, the thermal performance factor increases 42% and the mixing index increases 16.86% with respect to the rigid beam case. Finally, the flexible beam used here would not experience failure in the laminar flow regime.
Multi-objective optimization of a hybrid building integrated photovoltaic/thermal (BIPVT) system and earth-air heat exchanger (EAHE) is studied. According to the position of the BIPVT and EAHE systems, two different configurations (i.e. configuration A and configuration B) are examined. In the heating mode of the configuration A, the cold outdoor air is twice preheated by passing through the EAHE and BIPVT systems. In the cooling mode of the configuration A, the hot outdoor air is precooled by flowing inside the EAHE system and the photovoltaic (PV) modules are cooled using the building exhaust air. The cooling mode of the configuration B is similar to the configuration A, while in the heating mode of the configuration B, the outdoor air first enters the BIPVT collector and then passes through the EAHE system. The annual total amount of produced energy and exergy are considered as the objective functions. The effective parameters in the optimization process include the air mass flow rate, the length, width and depth of BIPVT channel and the length and depth of EAHE system. The outcomes revealed that the annual total energy and exergy outputs of the optimum configuration A are 96448.6 kWh and 10015.5 kWh, respectively, while these values for the optimum configuration B are respectively 98537.5 and 9888.4 kWh.
In this paper, details of the flow characteristics in a duct with circular corrugated channel mounted on walls were investigated both experimentally and numerically. In this research, in order to study the flow behaviors of corrugated ducts, the Particle Image Velocimetry (PIV) technique was used for obtaining extensive information. From this point of view, present experimental work, using the PIV method has been provided significant data about flow in corrugated channels. The aspect ratio of the investigated channel, a/R is selected as 1. The flow characteristics are studied as a function of four different Reynolds numbers, such as Re=2000, 3000, 4000 and 5000. Generally, the target of this comprehensive work is to investigate the flow characteristics and hydrodynamics in the circular corrugated channels in terms of instantaneous and time-averaged flow data such as velocity, streamline, turbulent kinetic energy, Reynolds shear stress and vorticity in the measurement plane. The findings have suggested that the corrugated channel have helped to improve both transporting energy and momentum transfer; hence, heat transfer rate was enhanced. The turbulence occurred in the corrugated channel with the aid of a sharp corner is the dominant factor for developing the entrainment between wake and core flows. Furthermore, in the presence of both negative pressure gradient and kinetic energy along the direction of flow, the vortices are readily mounded in cavity zones. Fluid flow can explain the phenomena of augmentations in heat transfer conveniently. At low Reynolds numbers, available cavities can cause increments in both heat transfer area and flow turbulence. On the contrary, at high Reynolds numbers, the secondary flow enables agitating hot and cold fluids in cavities besides enhanced turbulence in ribs region. In the separated shear layer zone, the entity of large coherent vortices and cyclical processes like discontinuous subtraction of the recirculation region into the core flow zone are demonstrated by instantaneous flow properties. The experimental measurements have been performed in the side view plane of a model which has the same geometry have been validated by computations. The comparative data have been showed that the distribution of velocity profile changed periodically and indicated good agreement between simulations and experimental results.
Passive latent heat thermal energy storage approach incorporating phase change materials (PCM) is a brilliant technique to tackle high energy consumption issue in buildings. This paper investigated the thermal performance of the conventional walls of buildings in Isfahan, Iran with the inclusion of thirteen different phase change materials. The studied base wall was composed of plaster (2 cm), clay brick (15 cm), and cement (3 cm). The effect of PCM position inside the wall on the heat transfer was assessed in two scenarios, namely: close to the interior and close to exterior. The nonlinear governing equations were solved using the finite volume method. The results show that the performance of PCM-based wall is strongly influenced by the thermal conductivity, phase-change enthalpy and melting temperature of PCM. A PCM can more efficiently reduce the heat transfer to the interior space in case it has a lower thermal conductivity, has a higher latent heat of phase-change, and its phase-change temperature is closer to the room temperature. Moreover, the thermal conductivity has priority over other PCM thermophysical properties. The lower PCM thermal conductivity leads to transfer the lower amount of heat to the interior space. A two-fold increase in the thickness of the PCM leads to less than a twofold reduction in the heat transfer. Among the studied PCMs, the heat transfer reduction by Enerciel 22 was within the range 15.6–47.6%, while this range was 2–7.8% for CaCl2.6H2O.
Stable Fe3O4-water nanofluids are prepared and sedimentation observation is used to investigate its stability. A convection heat transfer experiment is set up to investigate the thermo-hydraulic performances of Fe3O4-H2O nanofluids in a circular tube considering the effects of different nanoparticle mass fractions (ω = 1.0%, 3.0% and 5.0%), Reynolds Numbers (Re = 600–11000) and paralleled magnetic induction intensities (B = 0G, 100G, 200G and 300G). The result is that Nusselt number is proportional to nanoparticle mass fraction but opposite trend is found with the increasing paralleled magnetic induction intensity. Nanofluids with ω = 5.0% show the best performance of heat transfer. The resistance coefficient increases with mass fraction and can be enhanced by magnetic field further. Nanofluids with ω = 5.0% under magnetic induction intensity B = 300G show the largest resistance coefficient. A comprehensive evaluation index and an exergy efficiency evaluation plot are developed to discuss the thermo-hydraulic performances of nanofluids from quantity and quality. The thermo-hydraulic performance increases with nanoparticle mass fraction but decreases with paralleled magnetic induction intensity.
An experiment is carried out to research the thermo-hydraulic performance of TiO 2 -H 2 O nanofluids in triangle tubes while taking the effect of twisted tapes into consideration. The theories of thermal and exergy efficiency are applied to estimate this system. The influence of mass fractions of nanoparticles (0.1 wt%, 0.3 wt% and 0.5 wt%), Reynolds numbers (Re = 800–9000), different structures of triangle tubes (isosceles right triangle tube (tube 1), isosceles 45° triangle tube (tube 2)) and twisted tape on the Nusselt number, Nusselt number ratio, resistance coefficient, resistance coefficient ratio and pressure drop are experimentally studied respectively. Results show that there are three positive factors for heat transfer performance including large nanoparticles concentration, large Reynolds number and existence of the twisted tape. Compared with the smooth tube, tubes (tubes 1 and 2) with twisted tape can enhance heat transfer, but that without twisted tape can deteriorate heat transfer, for heat transfer performance, tube 2 is better than tube 1. Tube 2 with twisted tape has the biggest value of comprehensive performance index R3. A better exergy efficiency performance can be obtained when Reynolds number is greater than 5000 and the exergy efficiency reaches the best when Re = 8000.
A numerical study has been performed to investigate the flow and heat transfer characteristics of fluid flow through heat exchanger tubes fitted with perforated conical rings. The holes are circular, and the number of holes N is ranged from 0 to 10. The influences of perforated conical ring diameter ratios D 2 /D 1 =0.4,0.5and0.6 and the hole diameter ratios d/D=0.06,0.1and0.14 on average Nusselt number, friction factor and thermal performance factor are reported. This analysis is performed in the turbulent flow regime 4000⩽Re⩽14,000 and the governing equations are solved by using (RNG) k-∊ model. Due to strong turbulent intensity, perforated conical rings lead to more flow perturbation and fluid mixing between walls and the core region, which has a significant effect on heat transfer enhancement. The recirculating flow through the holes can also improve the heat transfer and reduce the pressure drop through the heat exchanger tube. The results show that the Nusselt number is reduced up to 35.48% by increasing the number of holes from 4 to 10. The maximum thermal performance factor of 1.241 is obtained for the case of N=10, d/D=0.1 and D 2 /D 1 =0.6 at Reynolds number of 4000.
In current modeling, turbulent heat transfer of homogeneous nanofluid due to inserting double twisted tapes has been carried out. To better describing performance of unit, generation of entropy has been examined. CuO nanomaterial has been dispersed in to H2O, to help its conductivity. The pipe was under the impact of uniform heat flux. Equations describing the flow and energy balance were solved applying finite volume method. The simulations illustrate that both augmenting pumping power and height of tape result in the reduction of thermal component and the augmentation of frictional component.
A numerical model has been developed for turbulent flow of hybrid nanofluids in a tube with wire coil inserts. The model was developed from van Driest eddy diffusivity equation. The model can be implemented with the consideration of new variables in eddy diffusivity of momentum and heat by using the coefficient, K and Prandtl index, ζ, respectively. The numerical analysis are undertaken for wide range of Reynolds number, different volume concentration, ϕ and various pitch ratio, P/D of wire coil. The numerical results were validated with the experimental data of TiO2–SiO2 nanofluids undertaken for wide range of Reynolds number and volume concentration. The final regression models of coefficient K and Prandtl index ζ were developed as a function of Reynolds number, Re or dimensionless radius, R⁺, volume concentration, ϕ and pitch ratio, P/D. A good agreement between the experimental data and numerical model indicating the validity of the numerical model for hybrid nanofluids with wire coil inserts. The numerical analysis was proved that the hybrid nanofluids contributes to higher Nusselt number and thus have better heat transfer performance compared to single nanofluids.
This paper provides a comprehensive review of published literature concerning heat transfer benefits of nanofluids for both macro-channels and micro-channels. Included are both experimental and numerical findings concerning several important performance parameters, including single-phase and two-phase heat transfer coefficients, pressure drop, and critical heat flux (CHF), each being evaluated based on postulated mechanisms responsible for any performance enhancement or deterioration. The study also addresses issues important to heat transfer performance, including entropy minimization, hybrid enhancement methodologies, and nanofluid stability, as well as the roles of Brownian diffusion and ther-mophoresis. Published results point to appreciable enhancement in single-phase heat transfer coefficient realized in entrance region, but the enhancement subsides downstream. And, while some point to the ability of nanofluids to increase CHF, they also emphasize that this increase is limited to short duration boiling tests. Overall, studies point to many important practical problems associated with implementation of nanofluids in cooling situations, including clustering, sedimentation, and precipitation of nanopar-ticles, clogging of flow passages, erosion to heating surface, transient heat transfer behavior, high cost and production difficulties, lack of quality assurance, and loss of nanofluid stability above a threshold temperature.
Flow and heat transfer characteristics of nanofluids in spiral tubes are experimentally studied. The effects of screw pitches (s = 10 cm, s = 12.5 cm, s = 15 cm), rotation angles (β = 0°, β = 45°, β = 90°) and nanoparticle mass fractions (ω = 0.0 wt%, ω = 0.1 wt%, ω = 0.3 wt%, ω = 0.5 wt%) on the flow and heat transfer performances are analyzed. Results show that Nusselt number increases with the decreasing screw pitch and the increasing nanoparticle mass fraction. It is also found that spiral tube with rotation angle β = 45° shows the largest heat transfer enhancement ratio, followed by rotation angle β = 0°, and the spiral tube with rotation angle β = 90° shows the smallest heat transfer enhancement ratio. In addition, a comprehensive evaluation index is applied to analyze the thermo-hydraulic performances of spiral tubes. One conclusion is obtained that there is a critical Reynolds number (Rec = 10,000) for the highest evaluation index, and the evaluation index increases with the decreasing screw pitch and increasing nanoparticle mass fraction. The evaluation index of nanofluids in the spiral tube can reach 1.24–1.25 at best.
The article presents a numerical investigation on turbulent thermal and fluid flow characteristics of multiple twisted tapes (MTTs) inserted sinusoidal rib tube (SRT) heat exchangers based on exhaust gas heat recovery background. The effects including geometric parameters of tape number (single, twin, triple and quadruple twisted tapes) and tape arrangements (clockwise and anticlockwise or co-swirl and counter-swirl) in the SRT were comparably studied. A periodic RNG k-ε numerical model was employed to depict the heat transfer behaviors and flow structures in the SRTs at a constant wall temperature condition. The results showed that the alone use of the SRT yielded enhanced heat transfer of about 27.4%–39.5% and increased friction loss of around 49.4%–74.7% higher than that in the baseline of spirally corrugated tube (SCT). In addition, it was found that the diverse thermo-hydraulic performances in the SRTs fitted with MTTs were dominated by flow structures of swirl flows and shear flows. By the synergy of longitudinal vortexes from SRT and MTTs, the Nusselt number and friction factor obtained from the SRTs fitted with MTTs were, respectively, larger than that from SCT at about 1.43–1.87 times and 2.66–10.07 times. In contrast to the SCT, the overall thermal performance evaluation criterion (PEC) was enhanced up to 1.59 for the alone use of SRT. Moreover, the PEC could be improved under increased heat transfer and reasonable pressure drop via suitable tape arrangements in the SRTs mounted with MTTs, of which the best PEC was 1.49. At last, the comparisons of present results with previous studies proved that the proposed enhanced devices held some competitive advantages.
A numerical study of two types of vortex generator (VG) have been conducted to enhance heat transfer of cooling in the battery thermal management system. The thermal behaviour and cooling effects have been investigated to evaluate the heat transfer performance of two types of VG. Air flow model coupled with a pouch cell model is carried out in this study. The results show that both types of vortex generators can enhance heat transfer before VGs, but only delta winglet VG can still enhance local heat transfer after it due to more vortices generated that can mix cold and hot air flow between the top and bottom thermal layers completely. It is found that the heat transfer enhancement is due to bulk fluid mixing, boundary-layer modification and flow destabilization by VGs. The maximum temperature of pouch cell is also numerically investigated by a validated battery model. The result shows that the maximum temperature of a pouch cell can be decreased by both delta winglet and rectangular rib. For the discharging rate at 5C, it can be decreased by 10% and the local Nusselt number can be increased by 38% compared to the baseline scenario without any VGs.
Phase change material (PCM) based heat sink is an appropriate technique for electronic devices cooling. PCM-based heat sinks have a low overall thermal conductivity. Using vertical fins is a brilliant approach to tackle low thermal conductivity issue. The aim of this study is to present a correlation to estimate the optimum number of fins and optimum PCM volume fraction in a PCM-based heat sink. The objective function is defined as the longest safe operating time of the device prior to reach the critical temperature. The independent parameters are heat sink height, fin thickness and heat flux. Around 900 various geometries of heat sink in the height range of 10–30 mm, fin thickness range of 0.2–0.5 mm were studied for two different input heat fluxes of 5000 and 10000 [Formula presented] to find the optimal number of fins. The analysis of variance was used to investigate the regression model reasonableness and find the main and interaction effects among the input parameters. The Results reveal that the optimal number of fins decreases by increasing the fin thickness. The increase in heat sink height results in higher optimal fin spacing, which consequently decreases the optimal number of fins. For a heat sink with constant width, a larger number of fins is required to prevent interfering with thermal performance, as the heat flux increases. The proposed correlations cover the Rayleigh number range of 3.3×10⁶≤Ra≤5.4×10⁸.
An experimental system is established to investigate the thermo-hydraulic performance of Fe3O4-water nanofluids in a corrugated tube under various magnetic fields. The influences of magnetic induction intensities (B = 0 G, 100 G, 200 G, 300 G), nanoparticle mass fractions (ω = 0.0%, 0.1%, 0.3%, 0.5%), electromagnet arrangement modes (one-side electromagnet and two-side staggered electromagnet), kinds of tubes (smooth tube and corrugated tube), Reynolds numbers (Re = 800–12,000) on flow and heat transfer characteristics are discussed. It is obtained that the augmentation of heat transfer is more sensitive to high nanoparticle mass fraction, high magnetic induction intensity, two-side staggered electromagnet and corrugated tube. A Comprehensive evaluation index is applied to estimate the thermo-hydraulic performance. It can be discovered that the comprehensive evaluation index increases with the increasing Reynolds number at first and then decreases, and the rough surface of corrugated tube delays the appearance of critical Reynolds number.
Heat transfer enhancement in parallel plate-fin heat exchanger is examined by performing three-dimensional numerical simulations of longitudinal vortex generators (VG) with protrusions. The turbulence is modeled using the shear-stress transport (SST) κ-ω model and validated with correlations and experimental data at Reynolds number equal to 4600. Hemi-spherical protrusions are inserted downstream two VG configurations: delta winglet type (DWP) and a new VG configuration named inclined projected winglet pair (IPWP), in various locations, leading to the definition of six different configurations. Based on the streamwise distribution of Nusselt number and friction coefficient criteria in addition to vorticity, the local performance is analyzed. Some VGs with protrusions are examined and show better performance relative to VGs standing alone. The present study highlights the different mechanisms involved in the convective heat transfer intensification by generating multiple interacting vortices while adding protrusions with low pressure drop penalty. Finally, it is found that the IPWP with protrusions, set downstream in the middle, bestows the best global performance with about 7.1% heat transfer enhancement compared to DWP configuration.
An experiment set for flow and heat transfer characteristics of nanofluids is established and the reliability of this experiment set is verified. Thermo-hydraulic performances of nanofluids flowing through a triangular tube with different structure twisted tapes are experimentally studied. The effects of nanoparticle mass fractions (ω = 0.1 wt%, 0.3 wt% and 0.5 wt%), Reynolds numbers (Re = 400–9000), different structure twisted tapes (P = 25 mm, 40 mm, 55 mm, 65 mm, 75 mm) on the Nusselt number and resistance coefficient enhancement ratios are experimentally investigated. It is found that the triangular tube with twisted tape can improve the Nusselt number by 52.5% and 34.7% at best in laminar and turbulent flow respectively compared with the corresponding smooth tube with the same fluid. The comprehensive performances of nanofluids in the triangular tube with twisted tape are also analyzed based on a comprehensive evaluation index. It is found that large nanoparticle mass fraction and small length of each twisted tape unit are more sensitive to the high comprehensive performance index. In addition, comprehensive performances between the triangular tube with twisted tape and the corrugated tube are compared. It is found that the triangular tube with twisted tape has an advantage over the corrugated tube in laminar flow.
Nanoparticles are an evolution in improving heat transfer by fluids that have the good potential for heat
transfer. Thus, in the last two decades, interest in researching them has increased dramatically. It has
been proved that the thermophysical properties of nanofluids are different from those of common fluids.
One of these properties is viscosity, which has a significant contribution to the calculation of the fluid
heat transfer. In the present study, a brief introduction of nanofluid and its applications have been discussed
in the first. Then, the classical equations suggested for predicting the viscosity of nanofluids
and their accuracy have been reviewed. The role of effective parameters on the nanofluid viscosity has
also been reported, indicating an increase in the viscosity of the common fluids by increasing the
nano-additives volume fraction and reducing it with increasing temperature. For the effect of increasing
nano-additives size, different results (decreasing or increasing) on fluid viscosity have been reported. The
effect of changing the type of nano-additives has also been described for a variety of metal/metal oxides
nanoparticles, and nanomaterial extracted from nature. In addition, nanofluids made with carbon nanotubes
are described according to the high heat transfer coefficient. Finally, the introduction of hybrid
nanofluid and their comparison with mono nanofluids has been explained by the conclusion that hybrid
nanofluids can well cover nanofluid weaknesses and improve its strengths.
In the present experimental study, an eco-friendly process (synthesized from rice plant source) was used to produce silica nanoparticles. Silica nanoparticles are environmentally friendly nanoparticles that have high heat transfer potential due to its abundant natural resources, low cost synthesis and mass production. The surface and atomic structure of the nanoparticles have been investigated through SEM and FTIR tests. After production of nanoparticles, water/silica nanofluid samples were prepared using two-step method that called eco-friendly nanofluid. Stability and thermal conductivity of the eco-friendly nanofluid were examined. Investigating the stability of the prepared samples, the DLS and TEM tests have been conducted as well as periodic visual observation of possible sedimentation over a period of six months through photography. The stability results indicated that the prepared samples possess excellent nano-structure and it showed long-time stability even after six months of preparation. The thermal conductivity measurement of the samples has been done in different temperatures ranging from 25 to 55 C and solid volume fractions of 0.1, 0.25, 0.5, 1, 1.5, 2, 2.5, and 3%. The results showed the maximum thermal conductivity enhancement of 38.2% which took place at the temperature of 55 C and solid volume fraction of 3%. Moreover, new precise correlation to predict the thermal conductivity of the eco-friendly nanofluid has been proposed with the maximum deviation of 2.72%. Finally, according to the results, it can be claimed that synthesis of environmentally friendly nanoparticles of silicon oxide with a plant source for nanofluid production is important, and this type of nanofluid can be introduced as an environmentally friendly alternative fluid with high heat transfer potential in thermal systems.
In this paper, the energetic and exergetic analyses of an inverted absorber multi-effect solar still has been studied. A new criterion was defined to determine the efficiency of the first law of thermodynamics for multi-effect solar stills. Energy and exergy balance equations have been developed for water basins, condensing surfaces and absorber plate to evaluate the irreversibility through the various components. Heat and modified mass transfer coefficients along with accurate properties of humid air were used to solve the governing system of differential equations. Results affirmed that the exergy loss through the absorber plate, water basins and condensing covers in a certain basin decrease as the number of effects increase. However, the increase in basins number from one to ten leads to increase in total irreversibility through the water basins by 337%. Calculations on energy balance equations showed that with increase in effect from one to ten, heat transfer to ambient decreased by 74.8%, which in turn increased the first law efficiency by 174.6%. It is found that with increase in effect from one to ten, the total yield, irreversibility and overall second efficiency increased by 407.3%, 10.4% and 471%, respectively, but global second efficiency decreased by 20.6%.
Surface cooling is an essential tool in many industrial applications. Effective utilization of the wetted surface area is an important factor in the heat transfer enhancement. It may be done by optimizing the shape of the extended surfaces meant for increasing the thermal diffusion, or by improving the thermal interaction between the solid and the fluid. Creation of differential pressure using vortex generator may improve the way the thermal energy is exchanged. It may be obtained by reenergizing the boundary layer using the generated vortices. In the present work the effect of surface textures of the vortex generator on heat transfer and vortex dynamics are studied. The CFD results show that multiple and single texturing on the leading and the trailing faces of the vortex generator, respectively, can enhance the primary vortex downstream of the vortex generator. This in turn enhances the heat transfer by increasing the average Nusselt number and the skin friction coefficient of the plate. The surface temperature is also found to be reduced by the stretching of the vortex with a minimal pressure drop
This study estimates the effect of functionalized multi walled carbon nanotubes on heat transfer and pressure drop of ethylene glycol–water flow in a tube. For this purpose, at the first, two-variable correlations as functions of temperature and solid volume fraction were proposed to predict the viscosity and thermal conductivity ratio of the nanofluid using experimental data. Then, the relative values of pressure drop and heat transfer coefficient were calculated by employing proposed correlations. Results revealed that the ratio of pressure drop decreased with increasing shear rate while increased with increasing solid volume fraction and temperature. Therefore, F-MWCNTs/EG-water nanofluid was more suitable for applications with higher shear rates. In addition, the ratio of heat transfer coefficient increased with augmentation of solid volume fraction and temperature. This ratio improved to 44%, which corresponded to the volume fraction of 1% and the temperature of 50 °C.
In this paper, the rheological behavior of nano-antifreeze consisting of 50%vol. water, 50%vol. ethylene glycol and different quantities of functionalized double walled carbon nanotubes has been investigated experimentally. Initially, nano-antifreeze samples were prepared with solid volume fractions of 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 and 1% using two-step method. Then, the dynamic viscosity of the nano-antifreeze samples was measured at different shear rates and temperatures. At this stage, the results showed that base fluid had the Newtonian behavior, while the behavior of all nano-antifreeze samples was non-Newtonian. Since the behavior of the samples was similar to power law model, it was attempted to find the constants of this model including consistency index and power law index. Therefore, using the measured viscosity and shear rates, consistency index and power law index were obtained by curve-fitting method. The obtained values showed that consistency index amplified with increasing volume fraction, while reduced with enhancing temperature. Besides, the obtained values for power law index were less than 1 for all samples which means shear thinning behavior. Lastly, new correlations were suggested to estimate the consistency index and power law index using curve-fitting.
In this paper, a mathematical model has been formulated to predict the performance of single and double effect solar still by using modified heat and mass transfer correlations. Two similar experimental desalination units (single and double effect) were designed to validate the mathematical model. The production of a solar still is strongly influenced by latent heat reuse and increase the temperature difference between the water and condensing surface. The results showed that the separation of condensing surface and solar energy receiving surface would result in enhancement of 94% for daily production compared to conventional one. Moreover, by reusing the latent heat the total yield of double effect showed a 70% increase with respect to a single effect. Increasing the power input from 200 to 500 Wm2 led to 236% and 240% production increase for single and double effect, respectively. Furthermore, raising the water depth from 1 to 3cm resulted in 14% and 26% decrease in the daily production rate of single and double effect respectively.
This paper examines the rheological behavior of water (60%vol.)–ethylene glycol (40%vol.) mixture in the presence of functionalized multi-walled carbon nanotubes. At the first, the viscosity of various samples was measured at shear rates ranging from 6.115 to 73.38 s⁻¹ and temperature range of 25–50 °C. Then, using the experimental data, some correlations were proposed to predict the viscosity of the nanofluid. Viscosity measurements at different shear rates revealed that all nanofluid samples were non-Newtonian power law fluid. Findings showed that consistency index increased along with volume fraction, while it decreased with increasing temperature. Moreover, the values of power law index were always less than 1, indicating shear thinning behavior.
The physical properties and especially viscosity and thermal conductivity are essential parameters for evaluating the heat transfer and flowing drag coefficients when designing a nanofluid system. This review presents a state of the art research progress of both the experimental and theoretical researches on viscosity and thermal conductivity of nanofluids. The results indicate that the viscosity and thermal conductivity of nanofluids are generally functions of particle loading, size, temperature and sometimes particle shape in their experimental range. Effect of material types is regularity on thermal conductivity but irregular on viscosity since the thermal conductivity of Graphene, CNTs, Au nanofluids is greatly higher than ordinary nanofluids but no orderliness could be found in viscosity for different particle types. Particle loading has a positive correlation with the relative viscosity and thermal conductivity but effects of particle size, shape, base fluid property and temperature are not unified. Although many influence factors have been considered, the main defect of the current modeling research is the failure of predicting the results in separate works due to the wide differences. Finally, the challenges and opportunities for the future studies are identified.
The Mixture model is applied to study the subcooled boiling of Alumina-water nanofluid in both vertical concentric annulus and vertical tube. The turbulence of the fluid is modeled through k–epsilon model. Local flow characteristics of subcooled flow boiling such as axial volume fraction and distribution of temperature are predicted. There is a very good agreement among the numerical and experimental results in the literature. This model is able to predict the distribution of temperature and the axial vapor volume fraction precisely. Variations of vapor volume fraction in conditions of constant velocity and mass flux in inlet are investigated and compared with together in different nanoparticles concentrations.