Introduction To Heat Transfer
Abstract
This book explains the physical concepts and methodologies of heat and mass transfer. It uses a systematic method for problem solving and discusses the relationship of heat and mass transfer to many important practical applications through examples and problems. It also presents the extensive use of the First Law of thermodynamics.
... The three main mechanisms of heat transfer that occur are namely convection, radiation and conduction. (Incropera, 2011) ...
... where conv is the convective heat transfer coefficient which is primarily material and geometry dependent, denotes the area of the object, while 1 and 2 being the temperatures of the two bodies involved in the heat transfer process or respectively one body and the surroundings. (Incropera, 2011) Free and forced convection are distinguished by the value of the convective heat transfer coefficient conv . A further distinction could be made for forced convection depending on the fluid and flow form involved. ...
... The equation for conduction is like that of convection, with cond standing for the coefficient of conduction heat transfer. (Incropera, 2011) ̇c ond = cond ( 1 − 2 ) ...
Sheet bulk metal forming or plate forging is an innovative hot stamping and forging process combination that allows the stamping of thick parts with complicated geometries in a single step with press hardening. Without a dedicated cooling system, the high process temperatures cause an eventual heating up of the die. This leads to reduction of the temperature gradient between the tool and part, hindering the in tool quenching effect and resulting in parts with reduced hardness and strength. Dies at elevated temperatures are also subject to accelerated wear and erosion. The aim of this thesis was to firstly analyse the cooling down of the hot forging die with conventionally manufactured cooling channels and then to investigate the possibility of implementing additively manufactured cooling channels. To that effect, a simulation methodology to model the effect of cooling channels in the hot forging die was developed. Firstly material characterization of the billet material 34MnB5 was carried out in a Gleeble machine using hot tensile tests and the resulting flow curves were implemented in a thermo-mechanical forming simulation in the software FORGE NxT. The simulation was used to analyse the temperature evolution within the die and billet during forming. The model was validated based on thermal and geometrical experimental measurements carried out on an industrial forging tool. Next, a tool equipped with conventional cooling channels was analysed in a coupled thermal-fluid simulation in LS-Dyna and the results showed that they were sufficient to maintain the forging die temperature between 100 and 150 °C. However, due to drilling artefacts, the main punch exhibited stress concen-trations close to the tool yield limit. The flexibility of additive manufacturing was uti-lized to design conformal cooling channels for the main punch by avoiding the critically stressed zones and their cooling effect analysed using thermal-fluid simulations. The conformal designs were able to cool the forging die by 30 °C more than the conventional cooling channels, while stress analysis revealed that they did not weaken the die. It was also concluded that due to the short contact times, the cooling channels in rapid hot forging dies cannot influence the temperature distribution of the part, rather only the die temperature can be influenced and controlled.
... In the past, inadequate heat dissipation incurred heavy costs. One of the best approaches to the problem is enlarging the heat transfer surface area, achieved by using fins [1]. Basically, fins extend the heat transfer surfaces and improve the rate of heat transfer from the surface of a body to its surrounding fluid [2,3]. ...
... Considering Eqs. (1)(2)(3)(4) and Eq. (16), Eq. (13) was rewritten as: ...
The homotopy perturbation method (HPM) was applied to analyze the thermal behavior of longitudinal radiative-convective moving fins with trapezoidal, concave parabolic, and convex profiles. The governing equation was extracted from the energy balance of a longitudinal element of the moving longitudinal radiation-convection fin. In addition, Heat transfer coefficient, thermal conductivity, and surface emissivity were assumed to be temperature-dependent. The HPM was used to solve the governing equation as it was a nonlinear equation. The HPM was validated by comparison to the differential transform method (DTM), finding good agreement. The dimensionless temperature, dimensionless fin tip temperature, heat transfer rate, and fin efficiency were compared in the parametric analysis. Additionally, the effects of changes of various dimensionless parameters such as thermal conductivity, emissivity, convective-conductive parameter, radiative-conductive parameter, and Peclet number on performance of the fins were invsetigated. The results indicated the HPM to be a powerful tool capable of rapidly and accurately solving such nonlinear equations as the energy equation governing longitudinal moving fins. Furthermore, the convex fin had 1% and 2% higher dimensionless tip temperatures than the trapezoidal and concave parabolic fins, respectively. The concave parabolic fin had 7% and 13% higher heat transfer rates and efficiency than the trapezoidal and convex fins, respectively. In addition, the concave parabolic fin is a more economical option than the other two as it is made of less material.
... 8 , 1 -1 1 ( 2 0 2 3 where v is the fluid flow velocity field. Ignoring fluid heat dissipation, the convective-diffusive heat transport equation can be described (Incropera and DeWitt, 2002) as, ...
... We use the Boussinesq approximation to account for density variations (Incropera and DeWitt, 2002), ...
We investigated the origin and spatio-temporal evolution of cooling fractures in pillow basalt which undergo thermal contraction after their eruption in an aqueous environment. Through a computer-based simulation using Fourier transformation, the thermo elastic stress displacement profiles within individual pillow units are determined. The scaled model (pillow diameter - 1 meter) generated radial, linear fractures perpendicular to pillow margin and irregular discrete flaws in the pillow interior like the ones observed in natural examples. Radial linear fractures of 3–5 centimetre in length have been measured in pillows of average one-metre diameter from the Maradihalli region, in the Chitradurga Schist Belt, India. An estimated time of 94–118 minutes was required to get radial fractures of similar length in the simulation. Our model efficiently replicated the generation and distribution of thermal fractures and allowed an estimation of cooling time for the peripheral glassy zone but has limitations in deciphering the formation of fracture networks in progressively crystalline inner zone of pillows.
... Re ----±6% 5 show the investigated results from the investigations were compared for the unadorned tube with the Dittus-Boelter correlations [28] and Gnielinski [29] for Nusselt number are given in Eqs. (12)-(13), Petukhov [30] and White [31] for the friction factor are given in Eqs. ...
The present work experimentally investigates the effect of novel turbulators on improving heat exchanger (HE) performance. Tests are conducted by insertion of three types of turbulators, 3PS, 4PS, and 5PS, including two pitch ratio PR (5-3.76). The results showed that the enhancement in heat transfer (HT) when using 5PS was more than the remaining two types. The greatest worth was at the lowest pitch ratio. The outcomes of experiments showed that the enhancement in the Nusselt number for each type of 5PS, 4PS and 3PS for small pitch ratio was 194%, 177% and 164% more than that of the plain tube, correspondingly. Also, the thermal performance factor, friction factor, and Nusselt number are all increased as the pitch ratio decreases. As a result, the small pitch ratio delivers a more considerable rate of HT and lower loss in friction. In addition, the results showed that the factor of thermal performance was more significant compared to unity for each type studied, and the maximum value of thermal performance factor acquired at η=1.54 is accomplished for the 5PS turbulators. The Correlations between the friction factor and Nusselt number were evolved for the range of Reynolds number (Re) of 12385 to 24766. The most relevant results of the evaluated study were presented to aid researchers in understanding the advances in HT enhancement in double pipe HE using novel turbulators inserts.
... The dynamic viscosity µ(T) and the thermal conductivity λ(T) of air, modeled as an ideal gas, were computed from the Sutherland equations [32]. The specific heat capacity C p (T) was obtained using the tabulated experimental data from [33]. A fourth-order polynomial regression was used to fit the data. ...
This paper introduces an innovative analytical model to compute flame velocities and temperatures within a premix burner in a domestic gas oven. This model significantly streamlines the heat transfer simulation process by simplifying the modeling of the thermo-chemical energy release during combustion, effectively reducing complexity and computation time. Accelerated solutions are essential at the initial design stages when comparing the effect of the oven parameter variation on the overall performance. The validation of the proposed analytical model involved experimental assessments of the temperature of the false bottom plate in a natural gas oven. The resulting data were then compared against CFD simulations performed utilizing the proposed model. The results revealed a marginal discrepancy of 4% between the experimental measurements and the outcomes generated by the model. Simulations were executed under differing conditions, encompassing scenarios with and without radiation effects. This exploration identified natural convection as the predominant heat transfer mechanism, with heat radiation contributing only modestly to the heating of the false bottom plate. Among its advantages, the proposed model offers a notable reduction in the numerical complexity of the modeling of the combustion process. Furthermore, its straightforward integration into numerical simulations involving premixed flames underscores its practical utility and versatility in evaluating design performance at the early stages of the design. Highly accurate models can be left for the final oven configuration validation.
... where hfree and hforced are the free and forced convection heat transfer coefficients, respectively, which are defined as (Kaplani and Kaplanis, 2014;Khanna et al., 2017) (18) where RaL is the Rayleigh number, which is defined as (Incropera and Dewitt, 1985) ( 19) with α and ν as thermal and momentum diffusivities of air, respectively, at the film temperature (Fujii and Imura, 1972). ...
The overall performance of PV-PCM integrated with rectangular straight fins is analysed by three-dimensional transient numerical simulations. The influence of fin lengths, number of fins (n), and inclination (θ) of the system is investigated and compared with the PV-only system, and an optimal system configuration is then identified. Finite element analysis is used to conduct the simulations using COMSOL Multiphysics 6.0. The PV front surface is subjected to a constant flux of 1000 W/m2 for 180 min, and the PCM employed is RT25HC. The results indicate that the average PV temperature tends to drop with increasing inclination and fin length, thereby enhancing the PV efficiency, with maximum improvement attained for the full fin case for a given inclination and number of fins. Compared to the PV-only system, the highest PV temperature reduction and PV efficiency enhancement are 59.65 °C and 45.1%, respectively, for the horizontal system of full-length fins with a number of fins equal to 6. The full-fin PV-PCM system with 6 fins and 45° inclination gives the highest instantaneous power output of 14.16 W. The melting rate of PCM is strongly related to the heat transfer rate inside PCM, and the lowest melting time is obtained for the 8-finned PV-PCM system with θ = 45°. The peak velocity magnitude for all systems with different fin lengths is also examined to analyse the extent of convection levels within PCM.
... Nusselt numbers which obtained by Dittus-Boelter (Eq. (12)) [45] and Gnielinski (Eq. (13)) [46] were critically compared. ...
The characteristics of heat transmission in a cylindrical tube equipped with novel
geometric turbulators inserts were investigated experimentally. The effects of two
geometric parameters (ratio of pitch P=L/D and interior angle) on fiction factor, Nusselt
number, the thermal executions were tested and compared with a smooth tube for the
same conditions. Reynolds number ranged from 4293 to 14310, with interior angles of
20°, 60°, and 95°, and pitch ratios between 4.44 and 5.83. The relation between friction
factor and Nusselt number for practical applications have successfully predicted. It was
revealed that friction factor, Nusselt number, and thermal performance enhanced with
reducing the pitch ratio and the interior angle. Nusselt number raised by 91,117 and
154%, friction factor enhanced by 82.7, 105.3 and 136.1 compared with smooth tube at
ratio pf pitch L/D=4.44 and interior angle θ=20°. The factor of thermal performance
was discovered to be larger than the unity for all arrangements and the maximum value
obtained at η=2.2.
... From the nature of the heat transfer and the type of flow, the Reynolds number (Re) or the Grashof number (Gr) must be calculated, and then the appropriate Nu correlations can be selected. For example, these correlations are given by previous studies [23][24][25][26][27][28][29][30][31][32][33][34][35]. ...
... Firstly, numerical results obtained from the present simulations are compared to a well known correlation result. Fig. 6(a) shows the Nusselt number as function of Reynolds number for the present numerical study compared to results computed from Dittus-Boelter Correlation [34]. As presented, the results shows a good agreement with minimum and maximum difference rates of 2% and 7% respectively taking into consideration that the Dittus-Boelter correlation fits best with ±20% uncertainty against their experimental data. ...
... The average Nusselt number for water is graphed versus the Reynolds number in Fig. 6. Additionally, the Nusselt numbers obtained from the classical correlation [46,47] are included for comparative purposes within the same figure. The findings reveal a satisfactory agreement between the results of this study and the predictions derived from the Dittus-Boelter equation. ...
In the present study, the effects of surfactant solutions on pressure drop properties and heat transfer characteristics in a double pipe heat exchanger have been investigated. An ionic surfactant (SDS) and two nonionic surfactants (NP-10 and Tween 80) solutions with 0.2 wt% are utilized at different flow rates. The results show that pressure drops for surfactant solutions are lower than those for water at equivalent flow rates. NP-10 demonstrates high drag reduction values, reaching a maximum of approximately 15%, whereas Tween 80 has lower drag reduction values, which vary according to the flow rate. Besides, Nusselt number for water in this study reveals a satisfactory agreement with the predictions derived from the Dittus-Boelter equation with a difference of 2.1%. While NP-10 and Tween 80 addition cause the Nusselt number to decline, SDS does not significantly alter it when compared to water. Energy correlations with high R² values have been developed using experimental data for water and surfactant solutions. Furthermore, enhancement factors (η), the ratio of heat transferred at constant pumping power with and without surfactant, have been calculated. The η values vary within a range of 0.8‒1.1 depending on the flow rate, and for SDS solution, these values are above 1 when the Reynolds number is in the range of 13000–25000. In the case of NP-10 and Tween 80 solution, the η values are below 1 for the whole flow rate range.
... To find ' ' and assess the instrument's dynamic performance, it would be necessary to apply sinusoidal-type temperature inputs, but it is difficult to generate this type of signal, so standard types are used, such as the step signal. There are three principal methods to determine ' ' [52][53][54][55][56][57]: ...
... Where stands for the heat of Ohmic losses, often known as Joule heating (W), I for battery current (A), and for internal resistance, which is made up of three terms: diffusion resistance, ion transport resistance, and Ohmic resistance [20]. ...
With a novel NSTDA design, pressure drop, and standard deviation of cooling water velocity inside the channel of the liquid cooling plate were evaluated under various channel counts [2, 3, 4, and 6 channels per base], inlet temperatures of water [25, 30, 35, and 40 °C], and inlet velocity of water [0.5, 1.0, 2.0, and 3.0 m/s] at steady-state conditions. It was found that the 4-channel design produced the most distributed flow with an inlet water velocity of 0.5 m/s. The average channel velocity was 0.0371 m/s. When increasing the inlet velocity of water, a larger pressure drop was observed. Simulation of heat transfer on a single row, single cooling channel design of a battery pack was performed with a channel velocity of 0.03 m/s, which imitates the 4-channel design under the heat generation produced at a charging rate of 0.75 C. An inlet temperature of 30 °C was used to keep the maximum temperature of the battery at 30.706 °C. The temperature difference over the battery pack was approximately 0.4 °C.
... VPI is used to provide encapsulation or impregnation of electrical windings with a good material penetration and/or deposition, which results in an improved electrical, mechanical thermal performance of the windings. However, the impregnation process is inherently prone to the impregnation imperfections like air pockets and/or cavities due to the winding arrangement, impregnating material and manufacturing process used [16]. These manufacture and assembly imperfections have been shown to have a significant effect on the winding equivalent thermal conductivity making the accurate estimation of the winding thermal properties challenging [17], [18]. ...
This paper presents an experimental approach for accurate derivation of equivalent thermal conductivity of anisotropic impregnated electrical windings. The proposed method employs a custom-built heat flow metering system for the analysis of cuboidal materials samples, which allow for the material anisotropic properties to be experimentally derived. Both theoretical fundamentals and experimental data from tests on 8 differing materials samples are discussed in the paper demonstrating the effectiveness of the proposed method. A comparison between various resins and winding geometries is made concluding that a rectangular winding with Epoxylite resin demonstrates the highest equivalent thermal conductivity in all planes. For sample planes with high thermal conductivities (i.e., 180W/m.K) a measured accuracy down to 1.81% was achieved. As predicted by numerical methods, sample planes with low thermal conductivity (i.e., 0.2W/m.K) had a much higher propensity for error. Further to these, an impact of accuracy of the thermal conductivity data on the winding temperature distribution is illustrated for a case study electrical machine demonstrator. The theoretical predictions show a significant effect, i.e., here, an increased winding to housing thermal resistance up to 17% when using measured thermal conductivity data for the proposed test setup.
... where r pi is the inner radius of the pipe; κ p is the thermal conductivity of the pipe material; and h p is the convection coefficient within the pipe as computed using the Darcy friction factor and the Gnielinski correlation. [28][29][30] The temperature of the water is modeled by ...
Thermal management of mass concrete can adversely impact a
project’s cost and schedule, both during planning and in execution.
Nomograms are presented as aids to quickly identifying and
making tradeoffs among promising thermal management options.
First, the temperature of fresh concrete and a worst-case adiabatic
temperature estimate is provided by a nomogram based on
simple physical models. A subsequent nomogram accounts for the
impact of size, shape, and environment and is based on a surrogate
model generated from many three-dimensional (3-D) finite
element simulations without postcooling. Finally, nomograms for
postcooling are given, similarly founded on finite element-derived
surrogate models, for two classes of cooling pipe layouts. The use
of these nomograms, with an awareness of their estimated error,
is discussed for the initial development of mass concrete thermal
management plans.
... A reflective insulation system is formed by installing reflective insulations in parallel, separated by one or more enclosed air spaces. This trapped air is designed to resist air movement and thus reduce the convective heat transfer [23]. ...
... The solution is obtained by introducing a similarity variable η = x / 2√+(, through which the heat equation is transformed from a partial differential equation, involving two independent variables (x and t), to an ordinary differential equation expressed in terms of the single similarity variable [154]. ...
Hollow-core photonic crystal fibers (HC-PCFs) can guide light inside the hollow core by photonic bandgap or inhibited-coupling mechanisms. HC-PCFs are now implemented as an important tool of laser beam delivery in place of traditional single mode optical fibers. One of the problems arising from high-power injection in the optical fiber is the probability of triggering the fiber fuse effect. This effect is related to a heat conduction process in optical fibers. The unsteady-state thermal conduction process in several HC-PCFs was studied theoretically by the explicit finite-difference method using the thermochemical SiOx production model. For heat conduction analysis, the complicated inner structure of HC-PCFs was simplified using the model composed of silica-ring and air-hole layers. In a kagome-lattice HC-PCF, the inclusion of metallic impurities in the silica struts was responsible for fiber fuse initiation. The calculated velocities of fiber fuse propagation in the kagome-lattice PCF were in fair agreement with the experimental values. Furthermore, the calculated velocities of fiber fuse propagation in two types of polymer-coated revolver fibers were in fair agreement with the experimental values. If the polymer coating of the revolver fiber is removed, the Fresnel reflection at the outer surface of the support tube occurs and the back-reflected light wave is incident upon the silica capillaries and the hollow core. To clarify the in-phase condition, we estimated phase changes of optical routes in the uncoated revolver fiber. It was found that the reflected waves from the outer surfaces of the silica capillary and support tube are in phase at the core-capillary boundary, and they are mutually enhanced as a consequence of the constructive interference. As a result, the power in the hollow core and the silica capillary was improved for the uncoated revolver fiber compared with the polymer-coated one. The calculated velocity of fiber fuse propagation in the uncoated revolver fiber was in fair agreement with the experimental value.
... Due to this, the majority of studies have concentrated on longitudinal vortex generators (LVGs) like delta wings, rectangular wings, delta winglet pairs, and rectangular winglet pairs [26][27][28][29][30][31][32][33][34][35][36][37]. Furthermore, winglet-type roughness elements have been utilized in solar air heaters [38][39][40][41][42][43]. Related previous research for comparative study with the present work is shown in Table 1. ...
In this study, a new envelope winglet vortex generator is numerically analyzed and installed on the hot side of the thermoelectric generator (TEG) exhaust heat exchanger. Experiments for the TEG-based waste heat recovery (WHR) system integrated with engine exhaust have identified the best design configuration for the envelope winglet vortex generator in terms of pitch/channel height ratio (P/H) and tilt angles (\(\theta\)). The system's feasibility has been proven by contrasting the current thermoelectric-based WHR with conventional alternator technology. Numerical research showed that the more significant flow rates in longitudinal envelope winglet VGs resulted in a larger radius. The envelope winglet profile has a sizable impact on the performance of the innovative TEG system with a vortex generator in the exhaust heat exchanger. The current analysis indicates that the exhaust heat exchanger arrangement with a pitch/channel height ratio (P/H) of 3 and a tilt angle (\(\theta\)) of 60° produces the system's best power output. Maximum power output and maximum net power output at engine load L3 are shown at \(\theta\)= 60° and 105 and 56.86% higher than those of the smooth channel, respectively. However, the largest power out and net power output increases are determined to be 68.08 and 42.28%, respectively, for P/H = 3. The recommended envelope winglet Vortex Generators (VGs) in engine operating mode L3 can raise brake-specific fuel consumption (BSFC) by up to 0.82%. The engine would operate at this mode's lowest fuel consumption and emissions.
... The present experimental results on heat transfer and friction characteristics in a smooth wall tube are first validated in terms of Nusselt number and friction factor. The Nusselt number and friction factor obtained from the present smooth tube are, respectively, compared with the correlations of Dittus Boelter for Nusselt number, and of Petukhov for friction factor found in the open literature [28] for turbulent flow in ducts. ...
The influence of inclined vortex rings (VR) on heat transfer augmentation in a uniform heat-fluxed tube has been investigated experimentally. In the present work, thevortex rings were mounted repeatedly in the tube with various angle (25 0 ,30 0 ,35 0) and geometry parameters of the VR, three relative pitch ratios (PR = P/D = 2, 1 and 0.5) and at constant relative ring blockage ratios (BR = b/D = 0.2). Air was employed as the test fluid in the tube for the Reynolds number from 12000 to 24,500. The aim at using the VRs is to create counter-rotating vortices inside the tube to help increase the turbulence intensity as well as to convey the colder fluid from the core regime to the heated-wall region. The experimental results show a significant effect of the presence of the VRs on the heat transfer and pressure loss over the smooth tube. The larger BR value provides higher heat transfer and pressure loss than the smaller. The Nusselt number is maximum for vortex ring angle 35 0 , but due to the large increase in the friction factor, thermal performance decreases. However, the VR at BR = 0.2 and PR = 0.5 with 30 0 yields the best thermal performance.
... Air used as the working fluid and its properties depicts in Table 1 according to the environmental temperature as 25°C.To generate a turbulent fluid flow, a centrifugal blower with a three-phase power supply is used. Under steady-state circumstances, the quantity of heat carried by the air would be equivalent to the calculated heat loss in the test portion [31].Therefore, ...
The study focused on conducting a heat transfer analysis of a circular tube heat exchanger with alternating solid-hollow inserts using the Ansys Fluent software version 19.0 and via experimental setup. The objective was to determine the heat exchanger tube's friction factor, heat transfer, and thermal performance factor (TPF) under steady state conditions. The investigation involved circular-hollow and solid inserts with diameters of 66 mm and 33 mm, respectively. The turbulence simulation was carried out within a Reynolds number range of 11,500–26,500, using air as the working fluid and the k-ε model for turbulence simulation. Three different insert arrangements were considered during the simulations. Among the different insert arrangements, the geometry with six inserts in the fluid domain exhibited the highest heat transfer while the geometry with five inserts resulted in the lowest heat transfer. However, the friction factor was minimum while using 5 inserts and increased significantly with the number of inserts increased similar results were found during experimental investigation. Even though the heat transfer was lowest with geometry having 5 inserts it yielded the highest TPF due to substantially less friction factor. Among the different insert arrangements and tested Reynolds numbers, the thermal performance factor was highest while using 5 inserts at Reynolds number 11,669, with a value of 1.421. Reynolds number was always kept equal to or greater than 11,500 to ensure the study under fully developed turbulent flow.
... The viscosity measuring unit also works with a constant-temperature pool. Thus, the viscosity measurements of the nanofluids prepared under the desired conditions were made in the range of 20-60 • C. The precision of the experimental data that was measured was compared to the reference data [49]. Fig. 2 compares the experimentally determined values of water, the base fluid employed in the creation of magnetic Fe 3 O 4 -water MNs, and the thermal conductivity and viscosity according to the temperature specified in the reference data. ...
... Moreover, variational principles can also be used to obtain simple analytical approximations, as will be shown further on in this paper [19,20]. In order to obtain the temperature distribution along a wall, a simple thermal model will be used, as can be found in many textbooks [21][22][23][24][25]. It will be shown, at the end of this paper, that this approach will be effective for the experimental measurements. ...
The paper is a continuation of the authors’ work intended for infrared navigation for blind people and mobile robots. This concerns the detection of obstacles in the person’s or mobile robot’s trajectory, in particular, the detection of corners. The temperature distribution of a building’s internal wall near a corner has been investigated. Due to geometry, more heat will be transferred by conduction so that inside the building, the temperature on the wall will be decreasing towards a corner. The problem will be investigated theoretically and numerically, and the results are confirmed by experimental measurements. The purpose of this research is to help blind people by equipping them with a small infrared camera that warns them when they are approaching a corner inside a building. The same aim is addressed to mobile robots.
... The local Nusselt number (Nu x ) is a function of the local heat transfer coefficient hydraulic diameter and fluid conductivity [24,27]. The internal local heat transfer coefficient (h x )is experimentally evaluated using the following equation [26]. ...
Waste heat recovery seems technically and economically feasible to extract more power from the available system. Thermoelectric-based waste heat recovery is one such technique for direct heat-to-power conversion. Improvement in heat transfer is coherent with the efficiency of such systems. In the current study, the thermal and hydraulic performance of the cold side of the thermoelectric generator is investigated by replacing the conventional parallel channel with the channel having non-parallel walls for heat transfer gains with a 0.1% vol. fraction of MXene nanofluid coolant. Experiments are performed under uniform heat flux with convergent, divergent, and flat ducts for three non-parallel angles 0⁰, 10, and 1.5⁰ within the Reynolds number 700-2100. Moreover, all performance is compared subject to the constraints of the same mass flow rate, pressure drop, and pumping power.
The result revealed that heat transfer efficiency rises with an increase in the converging and diverging angle. The divergent channel has a 15.62% and 17.18% greater value than convergent and smooth channels, respectively, at a Reynolds number of 2100. Also, compared to parallel channels, the pressure drop is greater in non-parallel channels. D-3 channel, and under identical pumping power and pressure drop conditions, D-2 performs better with a 0.1% vol. fraction MXene nanofluid coolant at identical mass flow rates. The flow acceleration or deceleration caused by the change in the cross-section of the channel has shown a strong influence on its heat transfer characteristic. The proposed design of the cold channel with MXene nanofluid will cause a profound enhancement in the power output of the thermoelectric system.
The hybrid boiler simulator is a simulation machine designed with two working functions, namely as a medical waste processing function and as a drying cabinet function. As a medical waste processor, this machine will focus on plastic medical waste, and as a dryer function, this machine will be a clothes-drying tool or cabinet. So based on the multifunctionality of the machine, this system has hybrid working characteristics. Hybrid boiler simulators can be a solution, providing the function of processing plastic medical waste and providing the advantageous function of economical and environmentally friendly drying. Therefore, this research aims to create a hybrid boiler simulator that can be used as a plastic medical waste processing machine and also as a clothes drying machine. The hybrid boiler system is designed by applying the concept of appropriate technology so that its implementation can be done easily and practically. The research implementation method is a classification of plastic medical waste, concept design, and analysis, construction design of a hybrid boiler system combined with an incinerator for burning medical waste, system function testing, and observation of test data. The focus of his research is the heat of burning plastic waste, heat radiation, circulators, and flow control systems as well as the characteristics of the results of burning plastic waste. The results of this research are that the hybrid boiler simulator machine can function as an incinerator machine to burn plastic medical waste and function as a clothes dryer; The function of the incinerator in this machine is only through two processes, namely the process of burning plastic medical waste raw materials and the process of burning carbon gas or smoke produced from the process of burning raw materials; the sumulator machine is not yet equipped with a fogging process for the function of smoke cleaning filter and fogging control; the hybrid boiler simulator machine works on the principle of automatic control based on temperature detection using a temperature sensor; The combustion temperature in the boiler machine can be controlled at a standard of 830 °C and the drying room temperature can be set at a room temperature of 50 – 150 °C.
This article presents a study of aerothermal performance of tubes with regularly-spaced multi-channel twisted tape elements (RS-MTT) installed. This research aimed to find the proper design RS-MTTs that induce swirl flow which potentially improves fluid mixing between the core fluid and the fluid near the tube wall, thereby accelerating the heat transfer rate. Additionally, the effects of Reynolds numbers and free-spacing ratios (s/y) on heat transfer, friction loss, and thermal performance behaviors were examined. The RS-MTTs having different free-spacing ratios (s/y) of 0.0, 0.25, 0.5, 0.75, and 1.0 were tested. Air was utilized as the testing fluid in experiments with Reynolds numbers (Re) spanning from 6000 to 20,000. The utilization of RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 augmented heat transfer rates up to 1.74, 1.80, 1.85, 1.90, and 2.15 times given by the plain tube alone while the friction factors increased by 4.22, 4.61, 3.87, and 4.05 times, respectively. At the lowest Reynolds number of 6000, the thermal enhancement factors of the tube containing the RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 reached the maximum values of 1.42, 1.35, 1.31, 1.27, and 1.23, respectively. Among the RS-MTTs tested, the RS-MTT with s/y = 0.0 showed the best thermal enhancement factor of 4.56%, corresponding to the heat transfer augmented of 11.52% with a friction penalty of 8.71%.
The purpose of this paper is to study numerically laminar mixed convection in a multiple vented cavity. This enclosure is continuously heated by constant temperature from the bottom wall, while the other boundaries are presumably thermally insulated. The imposed water-Al2O3 nanofluid flow is injected or sucked. The Influences of various control parameters, e.g.: Reynolds number Re, from 200 to 5000, the solid volume fraction of nanoparticles, , from 0to 7 %, and external flow mode (injection or suction) on the thermal patterns, the flow and the heat transfer within the enclosure are studied. Numerical results revealed that the presence of nanoparticles contributes to enhancement in the heat exchange and increase in the mean temperature within a cavity. Also, it was found that the heat performance and Applying the suction mode enhances the efficiency of cooling compared to the injection mode.
Description
The concepts and practices used in the designing oxygen systems, as well as the proper use of materials in oxygen-enriched environments. 26 peer-reviewed papers in 6 sections:
• Development and Evaluation of Test Methods
• Ignition and Combustion of Polymers
• Ignition and Combustion of Metals
• Analysis of Ignition Mechanisms
• Structured Packing for Cryogenic Air Separation Plants
• Miscellaneous
The thermal efficiency, heat transfer, and friction factor of a solar collector circulated with water diluted MgO nanofluid under natural circulation have been estimated. The tests were run with particle loadings of 0.1%, 0.5%, and 1.0% between the hours of 10:00 and 3:30. The greatest increase in Nusselt number has been reported for 1.0% vol. of nanofluid to be 21.48% and 37.28% higher than water at Re of 143 and 346, respectively. Larger friction factor penalties of 1.14 times and 1.27 times, compared to water, were simultaneously reported for nanofluid concentrations of 1.0% vol. at Re numbers of 143 and 346, respectively. The collector efficiency was larger from 57.15% to 65.47% when used with water and at 1.0% vol. The relative variances of the formulae created to assess the friction factor and Nusselt number are within 2.5%.
Extended surfaces are widely used in various engineering applications to introduce the large heat exchange area between the solid surface and the surrounding fluid. Surface modification in the form of ribs is a passive method of increasing the heat transfer rates at the solid-fluid interface by stimulating the fluid flow pattern inside the boundary layer.
The literature confirms that the heat transfer and friction from the ribbed surfaces are sensitive to the flow field near the wall, especially in the proximity of the ribs; therefore it is imperative to study the effect of geometrical parameters of the ribs on the heat transfer and friction under different fluid flow rates. It is believed that the presence of ribs in the span wise direction contribute to the heat transfer rates due to attachment of the flow in the portion where the ribs are absent and will again detach as the flow will encounter the artificial roughness.
The present work deals with the numerical investigation of heat transfer and friction from a rib roughened fin subjected to forced convection. Numerical data pertaining to heat transfer & friction from a rib roughened fin are generated by carrying out numerical simulations under the varied fluid flow conditions. The standard computational techniques have been used to solve the governing equations of fluid flow and heat transfer with the RNG based k-Ɛ turbulence model for a test fin under the specified thermal and flow conditions.
Present numerical model is validated by comparing the heat transfer results from the
standard experimental data. Using a validated numerical model, the data pertaining to fluid flow and temperature distribution for distinct configuration of test fin are obtained. The thermal & hydraulic performance of rib roughened fin with the different system and operating parameters been plotted as function of flow Reynolds number and geometrical parameters of rib roughened fin and it is discussed with respect to the heat transfer and friction characteristics of the rib
roughened fin. The results obtained from the rib roughened fin geometry are compared with that of a plain fin to determine the effectiveness of test fin in extracting heat from its base under similar operating conditions. The rib roughened fin has rib pitch to height ratio (P/e) of 6 and rib height of 2 mm has been found to have a maximum enhancement in heat transfer with a simultaneous increase in frictional losses than that of a plain fin.
The thermo-hydraulic behaviors of turbulent forced-convection heat transfer flow over a rectangular cross section baffled channel are numerically examined in various graded baffle plate ratio configurations ‘GBR = 0.10, 0.11, 0.12, 0.13, 0.14, and 0.15) at different Reynolds numbers, ranging from 12,000 to 32,000. The governing equations that describe the flow are integrated by the finite volumes method, in two dimensions, employing the Commercial CFD software FLUENT 6.3 with low-Reynolds-number k-E model to describe the turbulence. The velocity and pressure terms of momentum equations are solved with SIMPLE-algorithm. In particular, axial velocity, turbulence intensity, pressure, and temperature fields, average Nusselt number and friction loss are obtained. The numerical runs are carried out for different values of Reynolds numbers and graded baffle ratios at constant wall temperature condition along the top and bottom walls. Results were compared with available experimental data from the literature and good agreement is obtained.
There are various situations where it is desirable to obtain approximate analytic solutions. An obvious case is when an exact solution is not available or cannot be easily obtained. Approximate solutions are also obtained when the form of the exact solution is not convenient to use. Examples include solutions that are too complex, implicit, or require numerical integration. The integral method is used extensively in fluid flow, heat transfer, and mass transfer. Because of the mathematical simplifications associated with this method, it can deal with such complicating factors as phase change, temperature-dependent properties, and nonlinearity.
Smooth interactions between talkers can be realized by transmitting and receiving mutual video images and voices in remote communication. However, in such remote communication, it is difficult to generate a sense of unity and an interactive atmosphere because humans recognize screens as a boundary of the physical space. Therefore, it is essential to develop a communication system that can generate and share an interactive atmosphere and interaction-activated communication even if talkers are in remote places. In this study, we developed a speech-driven avatar robot system incorporating an estimation model that simulates the degree of activated communication based on the talker’s speech. The developed avatar robot system can visualize an interactive atmosphere while changing the complexion based on an estimated value. The effectiveness of the developed system was demonstrated by means of sensory evaluations.
The article examines the influence of delta-wing V-type baffles (DW-PVBs) on the average Nusselt number, local Nusselt number distribution, pressure losses, and thermal performance behaviors in a channel. Delta-wing perforated V-type baffles (DW-PVBs) mounted in a regular manner on the bottom of a channel produced two pairs of longitudinal counter-rotating vortices to enhance chaotic fluid mixing and destabilize the boundary layer, hence boosting the heat transfer. The geometric characteristics of the delta-wing V-type baffle (DW-PVBs) located on the bottom of the channel were examined at relative baffle blockage and pitch ratios (BR = h/H = 0.3 and p/H = 1.5), and five delta-wing attack angles, θ = 0o (solid V-shaped baffle), 22.5°, 45°, 67.5°, and 90°. The present DW-PVBs mounted on the channel were designed to mitigate pressure loss due to flow blockage. The experiment was done by permitting air to flow through a channel at Reynolds numbers (Re) ranging from 6000 to 24,000. The present results show that the friction factor using the DW-PVBs decreased considerably with increasing θ values. The experimental results revealed that small θ values yielded greater heat transfer and resistance than large θ values. The DW-PVBs with θ = 22.5° performed better than inserts with other θ values in terms of heat transfer rate. It was also observed that the DW-PVBs with θ = 45° gave the maximum thermal performance factor (TPF), while presenting a 13.64–17.26% lower friction factor than the solid V-shaped baffle. Furthermore, it was also found that the DW-PVBs with θ = 0°, 22.5°, 45°, 67.5°, and 90° gave peak TPF values of up to 1.87, 1.89, 1.91, 1.87, and 1.84 at the lowest Reynolds number, 6000.
This paper offers an experimental investigation of the effect of metal foam on the thermal and hydrodynamic performance of a parabolic trough collector (PTC). Metal foams play a crucial role in heat transfer improvement due to their high thermal conductivity. Three different arrangements of metal foams are applied inside the absorber tube of the PTC. The flow regime in the absorber tube is laminar at different Reynolds numbers of 422, 844, 1267, and 1689. Experimental tests are designed with Design-Expert software in which the response surface method is utilized. Experimental results revealed that maximum enhancement in thermal efficiency is related to the periodic array arrangement of the metal foam inside the tube. This arrangement leads to a 14% increase in thermal efficiency. However, in this arrangement, the friction factor increases considerably compared to a plain receiver tube.
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