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Viscosity of nanofluids: A review of recent experimental studies
... To perform simulations in heat exchangers, the viscosity must also be known. Here the viscosity test was measured by Ostwald viscometer as well the viscosity of nanofluids can be estimated by using Eq.(13) [38]: ...
... the experimental friction factor, ∆ is the pressure drop (Pa), L is the length of the tube (m), is the inner diameter of the tube (m), is the density of the nanofluid (kg/m 3 ) and v is the velocity of nanofluid (m/s).Comparison between the results of Eq. (15) and Eq.(16 and 17), the experimental and theoretical friction factor of the nanofluid inside the tube might be determined[37,38]: ...
In this work, an experimental system was established to measure the heat transfer characteristics, including the heat transfer coefficient, overall heat transfer, Nusselt number, and thermal conductivity. The investigation focused on spring water and tap water-based nanofluids containing Fe2O3 and ZnO nanoparticles with particle sizes of 50 nm and 70 nm, respectively. The experiments were conducted inside an automobile engine, studying the effects of varying nanoparticle volume fractions at a constant temperature. Fe2O3 and ZnO concentration in the respective based fluids was verified between 0.02 % and 0.08 % v/v and 0.01 and 0.07 %, respectively. The spring water is not so far used in the previous studies and is much more available in Kurdistan region. Reynolds numbers of nanofluids inside the engine were considered between 1000 to 8000 in a different range as that of the literature review. Reynolds analogy for heat and momentum has been employed in this study. It was observed that the thermo-physio-mechanical properties of nanofluids increased with increase in the concentration of nanoparticles and Reynolds number. However, the friction factor decreased with increasing Reynolds number but increased with an increasing volume concentration of nanoparticles. Generally, the results showed that the enhancement of the effective heat transfer of the nanofluids reached 46%, the overall heat transfer coefficient reached 39%, thermal conductivity reached 21.35% and Nusselt number reached to 38%. at 0.08% volume fraction of Fe2O3/spring water nanofluid. Based on all previous parameters estimated, the designed nanofluids in this study could be classified as a workable nanofluid in many industry applications
... This obstructs the nanofluid flow. When the temperature increases, it intensifies the thermally activated Brownian motion, weakens the interaction force between the nanoparticles and the base fluid, and reduces the flow resistance, resulting in a viscosity decrease [31]. Compared to other mainstream commercial hydraulic fluids [4,32] (Fig. 8c), the temperaturedependent viscosity variation (40-100 ℃) of the sample is relatively small, which is beneficial for improving the service stability and control accuracy of hydraulic systems under high-temperature conditions. ...
A novel liquid metal-based SiC/Graphene-Mo hybrid nanofluid (LMNF) has been fabricated. The nanoparticles are uniformly dispersed, and LMNF temperature-viscosity characteristics is stabler in a wider temperature range than traditional hydraulic media. With this, the LMNF tribological performance on Al 2 O 3 and SS316L friction pairs is studied: The LMNF has superior severe-pressure and high-temperature lubrication with the nanoparticle-enabled wear resistance. The SS316L surface forms composite nanofilm with the LMNF, which prevents adhesive wear and mitigates liquid metal corrosion. Comparatively, the nanoparticles function as "micro-bearings" on the Al 2 O 3 surfaces to assist lubrication. These benefits are reflected in the gear pump volumetric efficiency and wear rate of our industry-level hydraulic system, approving LMNF as a potential hydraulic transmission medium in harsh conditions.
... 28 Motivated by the superior thermophysical characteristics, both theoretical and experimental research on nanofluids has been greatly appreciated. [29][30][31][32][33][34][35] They have been utilized extensively over a wide range of applications including nano-drug and gene transportation, cancer therapy, solar panels, heat storage devices, vehicle brake fluids, radiators, fuel cells, and more. ...
The substantial temperature gradient experienced by systems operating at relatively high temperatures significantly impacts the transport characteristics of fluids. Hence, considering temperature-dependent fluid properties is critical for obtaining realistic prediction of fluid behavior and optimizing system performance. The current study focuses on the flow of nanofluids in a stationary cone–disk system (SCDS), taking into account temperature-dependent thermal conductivity and viscosity. The influence of Brownian motion, thermophoresis, and Rosseland radiative flux on the heat transport features are also examined. The Reynolds model for viscosity and Chiam's model for thermal conductivity are employed. The Navier–Stokes equation, the energy equation, the incompressibility condition, and the continuity equation for nanoparticles constitute the governing system. The Lie-group transformations lead the self-similar ordinary differential equations, which are then solved numerically. Multi-variate non-linear regression models for the rate of heat and mass transfers on the disk surface were developed. Our study reveals a notable decrease in the rate of heat and mass transfer when pre-swirl exists in the flow. The significant influence of nanofluid slip mechanisms on the effective temperature and nanofluid volume fraction (NVF) within the system is highlighted. Furthermore, the variable viscosity property enhances the temperature and NVF of the SCDS.
... The food industry, energy storage systems, advanced cooling technologies, solar energy collectors, and related sectors are the main industries that use nanofluids. Through experimental research, Choi [7] confirmed that adding nanoparticles to a fluid can improve its heat transfer rate, viscosity, thermal conductivity, and thermal diffusivity [8,9]. A new technique for increasing heat generation in magnetohydrodynamics (MHD) nanofluids in an asymmetrical channel with peristaltic motion was presented by Khan et al. [10]. ...
Current work focuses on increasing heat transmission in thermal systems with the incorporation of gyrotactic motile microbes, promoting the creation of structured fluids useful for bio-cooling and nanotechnology. This study explores the effects of electroosmosis and slip boundary conditions in a non-Newtonian Casson nanofluid with mass transfer. Specifically, it looks at bio-convection peristaltic events and conducts a thermodynamic analysis. The Arrhenius activation energy in an asymmetric channel is considered in this study. In addition, the authors evaluate viscous resistance, thermophoresis diffusion, porous surface properties, coupled convection, Brownian diffusion, and thermal viscosity behavior. The results obtained from mathematical expressions together with surface conditions are handled by means of a numerical algorithm implemented by means of the shooting technique through traditional program Mathematica, with the aid of its built-in tool, NDSolve. Many physical parameters, such as entropy generation, the Bejan number, velocity profiles, the density of gyrotactic motile microbes, and the accumulation profile of nanoparticles, are depicted graphically. The graphical study shows that entropy generation increases with a greater Helmholtz-Smoluchowski factor by 10%, but declines as the heat generation/absorption factor increases with same percentage. The Bejan number tends to increase with stronger heat sources by 5%. Application possibilities include improved control and effectiveness in mechanisms that include microfluidic equipment, systems for delivering medications, and biotechnological operations.
... In 2010, Tavman et al. 6 investigated TiO 2 , SiO 2 , and Al 2 O 3 nanoparticles in water, as well as a substantial increase in nanofluid viscosity as the nanoparticle concentration increased. In 2016, Bashirnezhad et al. 7 examined the viscosity of nanofluids containing solid nanoparticles is higher than that of typical working fluids, and quantifying the viscosity is required for building thermal systems. The expansion in thickness is legitimate by an expansion in nanoparticle volume portion and a decline in temperature. ...
The idea of probabilistic q-rung orthopair linguistic neutrosophic (P-QROLN) is one of the very few reliable tools in computational intelligence. This paper explores a significant breakthrough in nanotechnology, highlighting the introduction of nanoparticles with unique properties and applications that have transformed various industries. However, the complex nature of nanomaterials makes it challenging to select the most suitable nanoparticles for specific industrial needs. In this context, this research facilitate the evaluation of different nanoparticles in industrial applications. The proposed framework harnesses the power of neutrosophic logic to handle uncertainties and imprecise information inherent in nanoparticle selection. By integrating P-QROLN with AO, a comprehensive and flexible methodology is developed for assessing and ranking nanoparticles according to their suitability for specific industrial purposes. This research contributes to the advancement of nanoparticle selection techniques, offering industries a valuable tool for enhancing their product development processes and optimizing performance while minimizing risks. The effectiveness of the proposed framework are demonstrated through a real-world case study, highlighting its potential to revolutionize nanoparticle selection in HVAC (Heating, Ventilation, and Air Conditioning) industry. Finally, this study is crucial to enhance nanoparticle selection in industries, offering a sophisticated framework probabilistic q-rung orthopair linguistic neutrosophic quantification with an aggregation operator to meet the increasing demand for precise and informed decision-making.
... Researchers have studied the viscosity of nanofluids containing nanoparticles such as silicon dioxide, titanium dioxide, copper oxide, aluminum oxide, nickel, and carbon nanostructures in recent years. The majority of these studies, however, are focused on metal oxide nanoparticle suspensions [79,80]. Einstein [81] provided the first model for the viscosity of colloidal dispersion. ...
... However, other thermophysical properties, such as the nanofluid's density, specific heat, and dynamic viscosity, also play an important role in improving its heat transfer performance in several applications [3,4]. Nanofluids have been utilized in heating and cooling systems, electronics, transportation, and power generation, amongst other applications [5]. The flow behavior of several different nanofluids and the developed viscosity prediction models via four ML algorithms: GBR, RF, Adaboost, and voting regression. ...
The use of nanofluids in heat transfer applications has significantly increased in recent times due to their enhanced thermal properties. It is therefore important to investigate the flow behavior and, thus, the rheology of different nanosuspensions to improve heat transfer performance. In this study, the viscosity of a BN-diamond/thermal oil hybrid nanofluid is predicted using four machine learning (ML) algorithms, i.e., random forest (RF), gradient boosting regression (GBR), Gaussian regression (GR) and artificial neural network (ANN), as a function of temperature (25–65 °C), particle concentration (0.2–0.6 wt.%), and shear rate (1–2000 s−1). Six different error matrices were employed to evaluate the performance of these models by providing a comparative analysis. The data were randomly divided into training and testing data. The algorithms were optimized for better prediction of 700 experimental data points. While all ML algorithms produced R2 values greater than 0.99, the most accurate predictions, with minimum error, were obtained by GBR. This study indicates that ML algorithms are highly accurate and reliable for the rheological predictions of nanofluids.
... 38 Nanofluids possess several superior properties compared to simple fluids, including adjustable viscosity, density, and surface tension. 39,40 These properties enable precise control over droplet spreading and impact dynamics. Therefore, nanofluids hold potentials to meet specific requirements in a wider range of circumstances and hold significant potential for a broader array of applications. ...
Droplet impact on solid substrates is a ubiquitous phenomenon in nature, agriculture, and industrial processes, playing a crucial role in numerous applications including self-cleaning, pesticide utilization, and inkjet printing. As a promising technique, adding nanoparticles into simple fluids to form nanofluids can effectively manipulate droplet impact behaviors. However, a comprehensive understanding of how nano-particles modify the droplet impact dynamics, especially on the nanoscale, is still far from being fully explored. Hence, in this work, through the combined effort of molecular dynamics simulations and theoretical analysis, we elaborate on the influences of nanoparticles on droplet impact process. Using simple droplets as a control, we summarize four typical droplet impact modes and reveal how nanoparticles alter the impact behaviors of droplets, taking into account the key parameters including substrate wettability, impact velocity, volume fraction, and mass fraction of nanoparticles. We also demonstrate that with appropriate modifications, the theoretical/empirical models to predict the maximum contact diameter and the occurrence of breakup for simple droplets still hold to predict those of nanofluid droplets. Our findings and results enhance the understanding of the impact of nanoparticles on the droplet impact dynamics, with promising possibilities for various applications where regulating droplet impact behaviors is desired. Published under an exclusive license by AIP Publishing. https://doi.
... The formation of Al-Cu-Mg phase at high temperature reduces the amounts of deleterious MgCu 2 and MgZn 2 by depleting the liquid from Mg and Cu elements. The reduction in volume fraction of eutectic phases can also be attributed to the capacity of nanoparticles to reduce the permeability and increase the viscosity of nanofluid, resulting in a decrease in normal liquid velocity [45,46]. Yuan et al. [45] showed that the volume percentage of the eutectic phases is directly related to liquid velocity in Al7034 alloy during conventional casting. ...
The formation of solidification cracks during fusion welding of high strength and highly alloyed wrought aluminum alloys has been a significant challenge over the years. Recently, using TiC nanoparticle-enhanced filler metals was found to be an effective way for solidification crack elimination during TIG welding of Al7075 sheets. However, the impact of welding parameters on weldability in the presence of nanoparticles is still not completely understood. Therefore, the present research investigates the weldability of 3-mm thick Al7075 sheets with TiC nanoparticle-enhanced filler metal (Al7075) during TIG welding. Two sets of welding parameters, leading to two different heat input levels, are studied. The experimental results show that the filler metal effectively eliminates solidification cracks in both joints. Microstructure evaluations show an equiaxed grain morphology in fusion zones with an average grain size of 19.6 ± 2.6 and 26.2 ± 1.5 μm for joints welded with low and high heat input, respectively. However, statistically similar microhardness values are measured on both joints, suggesting no significant impact of the grain size.
... 36 Such importance cannot be overemphasised since many studies rely on theoretical modelling where often the effect of viscosities on material behaviour is underestimated. 37 In this work, experimental studies were undertaken with the view of understanding how the average particle size distribution (APS) of SiO 2 nanoparticles and their specific surface area (SSA) have an effect on the viscosity of the nanofluids and their resulting polymer/nanoparticle hybrids. In addition, such variants were studied on how they affect the (in)stability of the colloidal silica dispersions or their resulting polymer/nanoparticle hybrids. ...
This study investigated the relationship between variations in the size distribution and the specific surface area of SiO2 nanoparticles and the in(stability) and rheology of their colloidal dispersions and their resulting silica-poly(acrylamide) hybrids. Thus, SiO2 nanoparticles with size distribution in the range 40-173 nm, corresponding to 70-26 m2/g of specific surface area, were used in the studies. The results show a correlation between the average particle size distribution/the specific-surface area of silica nanoparticles with the in(stability) and the rheology of their dispersions, such that an increase in the particle size distribution from 40 to 173 nm corresponds to a decrease in dispersion instability index from 0.913 to 0.112. However, in the silica-poly(acrylamide) hybrids, a change in the particle size distribution from 40 to 173 nm corresponds to an increase in the nanofluid instability index from 0.1913 to 0.929. In the hybrid materials, interactions between polymer chains and nanoparticles lead to size-induced stability and rheological behaviour, such that the broadening of the FTIR peak around 1,000 cm-1 in the nanohybrids was related to an Si-O-H bending vibration that arose because of dominating hydrogen bonding arising from the interaction of the hydroxyl groups and the amide groups in the polymer. The rheological characteristics of the hybrid nanofluids show that the relative viscosity and shear sensitivity of the colloidal dispersions or their hybrids can be tailored by the average particle size distribution of the nanoparticles.
... Practically, a stable nanofluidic medium can be prepared physicochemically under specific experimental protocols [11] using known working fluids (e.g., toluene ethylene glycol, water, isopropyl alcohol, polydimethylsiloxane, propylene glycol, and kerosene) with a feeble volumetric fraction of solid nanoparticles (e.g., alumina, titanium, copper, gold, and carbon nanotubes). The latest experimental findings related to nanofluidic mixtures [12,13] ascertained experimentally that the insertion of solid nanomaterials in a viscous fluidic medium can modify enormously its thermophysical, optical, and chemical characteristics [14][15][16][17][18]. Due to their adjustable thermal efficiency, the nanofluidic mixtures were extensively employed in various engineering applications [19][20][21][22] (i.e., heat exchangers, heat accumulators, boilers, pipeline heat losses, crude oil refining, atomic reactor cooling, and heating/cooling of buildings). ...
Owing to the latest progression in the rheology of non-homogeneous composite media, viscoelastic materials have nowadays gained outstanding interest from experimenters because of their practical uses in different scientific areas (e.g., lubrication processing, blood vascular systems, polymer treatment, and petrochemical industry). Keeping in mind these vital applications, a realistic passive control approach has been applied in this numerical scrutinization to explore the aspects of radiating viscoelastic nanofluids during their MHD mixed convective flows nearby a sucked impermeable surface in the existence of an exponentially lessening heat generation. By invoking the constitutive rheological equations of Jeffery’s model and including the convective mass transport contribution along with the thermophoresis and Brownian diffusive mechanisms, the mathematical formulation of the flow model has been derived properly under the boundary layer assumptions. After a specific numerical treatment of the resulting boundary layer equations, several tabular and graphical demonstrations have been drawn accordingly. In this respect, it is demonstrated that Jeffery’s and Deborah’s numbers exhibit dissimilar behaviors toward the nanofluid motion and the resulting transport phenomena. As important findings, it is noticed that the convective heating and radiative heat transfer mechanisms enhance considerably the heat exchange rate with a slight weakening in the drag forces at the vertical surface. Whilst, the suction process shows an advantageous impact on these quantities of interest with a feeble perturbation in the surface temperature and nanoparticles concentration.
... Viscosity is strongly influenced by various parameters such as temperature [86][87][88][89][90][91][92][93][94][95][96][97][98][99][100], SVF [101][102][103][104][105][106][107][108][109][110], SR [111][112][113][114][115], preparation method [116][117][118][119][120], and NP size [121][122][123][124][125][126][127][128][129][130]. Hammat et al. [131] investigated dynamic viscosity of HNF consisting of MWCNT, SiO 2 NPs inside 5W50 engine oil in T = 5-55 • C, SR= 50-800rpm and SVF= 0-1% experimentally and statistically. ...
... The GR NPs and molybdenum disulfide can be uniformly distributed in the base fluid and it is reported that the velocity is high with isothermal wall temperature [89]. The viscosity of the NF also effects the HT rate [32,90]. The GR has ultra-thin thickness and maintains its transparency and conductivity when it is formally in contact with some rough surface. ...
... Its density, kinematic viscosity, [10] dynamic viscosity and specific heat are the most significant characteristics needed to estimate nanofluids. For different combinations, the thermal properties of nanofluids are experimentally carried out and the effects of the experiments are traced and contrasted with separate nanofluids samples. ...
... Although the benefits for improving volumetric direct solar-thermal conversion have been widely demonstrated by the uniformly dispersed nanofluids, the influence of added solar absorbers on other important thermophysical properties such as viscosity and effective thermal conductivity has not been fully revealed [122]. Typically, the viscosity of nanofluids increases with added fillers and is affected by their loading, size, shape, dispersion state, and surface chemistry [123]. In comparison with bare fillers, the surface-modified particles could generally minimize the increasing of viscosity because these surface-capping agents improve their chemical compatibility with the thermal storage fluids. ...
Direct absorption of sunlight and conversion into heat by uniformly dispersed photothermal nanofluids has emerged as a facile way to efficiently harness abundant renewable solar-thermal energy for a variety of heating-related applications. As the key component of the direct absorption solar collectors, solar-thermal nanofluids, however, generally suffer from poor dispersion and tend to aggregate, and the aggregation and precipitation tendency becomes even stronger at elevated temperatures. In this review, we overview recent research efforts and progresses in preparing solar-thermal nanofluids that can be stably and homogeneously dispersed under medium temperatures. We provide detailed description on the dispersion challenges and the governing dispersion mechanisms, and introduce representative dispersion strategies that are applicable to ethylene glycol, oil, ionic liquid, and molten salt-based medium-temperature solar-thermal nanofluids. The applicability and advantages of four categories of stabilization strategies including hydrogen bonding, electrostatic stabilization, steric stabilization, and self-dispersion stabilization in improving the dispersion stability of different type of thermal storage fluids are discussed. Among them, recently emerged self-dispersible nanofluids hold the potential for practical medium-temperature direct absorption solar-thermal energy harvesting. In the end, the exciting research opportunities, on-going research need and possible future research directions are also discussed. It is anticipated that the overview of recent progress in improving dispersion stability of medium-temperature solar-thermal nanofluids can not only stimulate exploration of direct absorption solar-thermal energy harvesting applications, but also provide a promising means to solve the fundamental limiting issue for general nanofluid technologies.
... Viscosity is an important thermal property which influences the the fluid's resistance and leads to an increase in pump work as the viscosity increases. Therefore, a precise prediction of viscosity is essential for the use of heat transfer fluid medium in these and other fields [10] to build the thermal system and calculate the necessary pumping power [11]. ...
In terms of heat dissipation, nanofluids with strong thermal conductivity are becoming more and more common, attracting more and more research and attention to date.In this study, Al2O3-H2O nanofluids were studied using molecular dynamics simulations and model parameterization. The dynamic viscosity distribution patterns were obtained at various temperatures(290K~360K), nanoparticle volume fractions(1.24%~6.2%), and particle sphericity(0.69~1.0), and an efficient ternary second-order polynomial viscosity prediction model was proposed on the basis of these results.The findings demonstrate the model's goodness-of-fit with a coefficient of determination over 0.96 and a root mean square error under 0.05, as well as its high predictive ability with a maximum relative error between simulated and predicted values under 9%. Using this viscosity prediction model, a subsequent parametric sensitivity study showsthat the volume fraction had the most significant impact on viscosity, exhibiting not just a second order effect but also an interacting effect with temperature and sphericity. The relative nanofluid viscosity, which is the ratio of nanofluid viscosity to aqueous base fluid viscosity, exhibits a convex parabolic growth at constant temperature and sphericity and increases more quickly at the same volume fraction the higher the temperature. The viscosity of the nanofluid increases by up to 34% when the volume fraction is equal to 6.28% and the particle sphericity is equal to 1.An efficient viscosity prediction model makes it easier to control important variables to reduce energy consumption during flow and increase its capacity to dissipate heat.
... The GR NPs and molybdenum disulfide can be uniformly distributed in the base fluid and it is reported that the velocity is high with isothermal wall temperature [89]. The viscosity of the NF also effects the HT rate [32,90]. The GR has ultra-thin thickness and maintains its transparency and conductivity when it is formally in contact with some rough surface. ...
The evaporative cooling system (ECS) is one of the cheapest and oldest cooling technologies. The conventional single stage ECS is most widely used in domestic application, particularly in hot and dry regions. However, in this system, the temperature of the air cannot be reduced below the wet bulb temperature of the air. The multistage ECS system helps to overcome this problem. The combination of direct and indirect ECS helps to reduce the temperature of the air below its wet bulb temperature. The further reduction in air temperature may be achieved with the help of the cooling coil driven by vapour compression system. The energy consumed by the ECS is lower as compared to vapour compression refrigeration system. The ECS can be driven with the help of solar power. The conventional cooling pad used in ECS can be replaced with locally available natural fibers to reduce initial cost and to reduce dependence on import of cooling pads. The performance of the ECS can be improved with the help of heat pipe. Various techniques are used to enhance ECS's performance. The performance of the vapour compression refrigeration system can be improved with the help of ECS. This paper discusses basics and types of ECS, methods used to increase the performance of ECS, types of natural fiber cooling pad material, process variables affecting ECS, recent technical advancements, challenges and opportunities.
... Similarly, in Equation (7), the dynamic viscosity of nanofluids with very low volume concentrations of nanoparticles is given by the Einstein model of 1906 [25]: ...
Nanofluids are generally utilized in providing cooling, lubrication phenomenon, and controlling the thermophysical properties of the working fluid. In this paper, nanoparticles of Al2O3 are added to the base fluid, which flows through the counterflow arrangement in a turbulent flow condition. The fluids employed are ethylbenzene and water, which have differing velocities on both the tube and the shell side of the cylinders. A shell tube-type heat exchanger is used to examine flow characteristics, friction loss, and energy transfer as they pertain to the transmission of thermal energy. The findings of the proposed method showed that the efficiency of a heat exchanger could be significantly improved by the number, direction, and spacing of baffles. With the inclusion of nanoparticles of 1% volume, the flow property, friction property, and heat transfer rate can be considerably improved. As a result, the Nusselt number and Peclet numbers have been increased to 261 and 9.14E+5. For a mass flow rate of 0.5 kg/sec, the overall heat transfer coefficient has also been increased to a maximum value of 13464. The heat transfer rate of the present investigation with nanoparticle addition is 4.63% higher than the Dittus–Boelter correlation. The friction factor is also decreased by about 17.5% and 11.9% compared to the Gnielinski and Blasius correlation. The value of the friction factor for the present investigation was found to be 0.0376. It is hence revealed that a suitable proportion of nanoparticles along with the base fluids can make remarkable changes in heat transfer and flow behavior of the entire system.
The present work addresses the shortcomings of heat transfer fluid behavior by emphasizing solutions for improved stability, enhanced thermal properties, and environmental sustainability. The study introduces an innovative hybrid nanofluid combining silicon dioxide (SiO2) and cellulose nanoparticles (CNP) into analytical‐grade Palm oil, adopting a two‐step methodology. This endeavor represents a significant advancement in exploring SiO2–CNP‐Palm oil hybrid nanofluids, positioning them as promising candidates for advanced heat transfer media. Physical characterization analysis confirms the successful integration of SiO2 and CNP into analytical‐grade Palm oil. The nanosuspensions of CNP‐Palm oil, SiO2‐Palm oil, and SiO2/CNP‐Palm oil are prepared at varying volume concentrations. All nanosuspensions demonstrated good stability after ultrasonication, as evidenced by optical performance and sedimentation studies, which endure for up to 60 d. Fourier transform infrared (FT‐IR) analysis further substantiates the chemical stability, revealing no emergence of peaks associated with the diffusion of nano‐additives. The thermogravimetric analysis (TGA) also affirms superior thermal stability in all nanosuspensions compared to base fluids. Rheological studies indicate that Palm oil exhibits Newtonian behavior. The nanofluid containing 0.1 w/v% SiO2/CNP nanoparticles exhibits a significant enhancement in thermal conductivity, showcasing an impressive 81.11% improvement. In addition, the nanofluid demonstrates an increase in viscosity with higher nanoparticle concentrations and decreased viscosity with rising temperatures.
Accurate estimation of thermophysical properties of hybrid nanofluids, such as thermal conductivity (THC), viscosity, and heat transfer performance (HTP), is crucial in energy applications and heat transfer. In this research, a comprehensive
experimental and computational investigation has been performed to predict the heat transfer performance (HTP) and thermophysical properties of a new hybrid engine oil-based nanofluid comprised of Mg(OH)2 and multi-wall carbon nanotubes
(MWCNTs) based on the temperature and the volume fraction of solids. Due to this aim, a new hybrid meta-heuristic dataintelligent method, called teaching–learning-based optimization integrated with an adaptive neuro-fuzzy inference system (ANFIS-TLBO), was developed. The proposed ANFIS-TLBO approach for the prediction of the HTP and thermo-physical properties of the engine was evaluated for robustness using the standalone ANFIS, multi-layer perceptron Artificial Neural Network (ANN), and multivariate adaptive regression spline (MARS) model. For the construction of the models, the temperature and the volume fraction of solids were utilized as the input features. At the same time, the output variables were HTC values for the internal laminar and turbulent flow regimen (HTPL and THPT), THC, and dynamic viscosity. The robustness and efficiency of the machine learning (ML) models were assessed using the root mean square error (RMSE), mean absolute percentage error (MAPE), and correlation coefficient (R). The outcomes of ML models reveal that the ANFIS-TLBO outperformed the other models. A piece-wise relationship for every target was extracted using the MARS model based on temperature and volume fraction. Besides, the outlier detection and statistical validity revealed the primary model's reliability and promising predictability potential for accurate estimation of thermophysical properties of hybrid nanofluids.
Thermal management is a critical challenge in advanced systems such as electric vehicles (EVs), electronic components, and photoelectric modules. Thermal alleviation is carried out through the cooling systems in which the coolant and the heat exchangers are the key components. The study examines recent literature on nanofluids and heat exchanger tubes along with state-of-the-art concepts being tested for heat transfer intensification. The performance of nanofluids in several common heat transfer tubes' geometries/configurations and the effectiveness of novel heat transfer augmentation mechanisms are presented. Promising results have been reported, showing improved heat transfer parameters with the use of nanofluids and intensification mechanisms like turbulators, fins, grooves, and variations in temperature and flow velocity. These mechanisms enhance dispersion stability, achieve a more uniform temperature distribution, and reduce the boundary layer thickness, resulting in lower tube wall temperatures. Moreover, introducing flow pulsations and magnetic effects further enhances particle mobility and heat exchange. However, there are limitations, such as increased frictional losses and pressure drop due to magnetic effects. The combination of nanofluids, novel heat exchanger tube geometries, and turbulators holds great promise for highly efficient cooling systems in the future. The study also presents a bibliometric analysis that offers valuable insights into the impact and visibility of research in the integration of nanofluids into heat transfer systems. These insights aid in identifying emerging trends and advancing the field towards more efficient and compact systems, paving the way for future advancements.
Researchers and engineers are actively working on enhancing the efficiency of heat exchangers in engineering applications by developing novel designs, exploring new materials, and utilizing nanofluids. Three kinds of nanofluids with varying concentrations are investigated in this paper. The objective is to assess the performance of N‐shaped double‐pipe heat exchanger used in thermoelectric power plants. The performance has been evaluated using COMSOL Multiphysics software. The findings show that higher nanofluid concentrations resulted in elevated heat transfer coefficients and improved efficiency of N‐shape double pipe heat exchanger. The analysis revealed that a mere 1% rise in the volume fraction of nanofluids enhanced the efficiency of the heat exchanger on average 23% when compared to the base fluid (water). In comparison to the N‐shape double pipe (Inconel 625) heat exchangers, the N‐shape double pipe (copper) heat exchangers appear to be more efficient. The introduction of nanoparticles has a notable impact on the heat transfer coefficients. Specifically, within an N‐shaped double pipe (copper) heat exchanger, the inclusion of a 1% volume fraction results in a 2.09% enhancement in the heat transfer coefficient for Al2O3/water, a 1.3% improvement for Fe3O4/water, and a 1.15% increase for TiO2/water. It also exposed that adding 1% Al2O3/water led to a significant 0.623% increase in effectiveness, while TiO2/water showed a 0.259% rise, and Fe3O4/water exhibited a 0.375% improvement. Moreover, increasing the Reynolds number enhances the Nusselt number for Al2O3/water and Fe3O4/water nanofluids by 55.22%, and for TiO2/water by 54.60% at a 6% volume concentration, leading to additional increases in exchanger efficiency. Therefore, the augmentation in nanofluid concentration leads to a reduction in the temperature pinch points both at the intake and outflow. This observation suggests that nanofluids exhibit a superior ability compared to conventional fluids when it comes to effectively lowering temperatures.
The paper presents the calculation estimates for efficiency of regenerative cooling for a model cylinder-shaped flow duct using a suspension of heat-conductive metal nanoparticles in n-decane as fuel/coolant. We adapted a standard mathematical model of conjugated heat transfer that accounts for thermophysical properties of the metal nanoparticle suspension and n-decane. The data are presented for heating up the nanosuspension and the model duct walls for the cases of different content of metal nanoparticles in nanosuspension. There exists a range beneficial for heat transfer from n-decane.
This article analyzes the impact of conjugated dissipative radiative heat transfer with heat source/sink, thermal slip, and the transverse magnetic field on the behavior of the magnetohydrodynamic (MHD) peristaltic thrust containing ferromagnetic gold nanoparticles (AuNPs) with different shape factors through the non‐Newtionian blood flow within compliant walls tube. Entropy generation (EG) plays a prominent role in all aspects connected to thermodynamics and heat transfer aiding in the identification and reduction of system irreversibilities. The sources of irreversibility stem from dissipative friction inherent in fluid flow, the presence of a magnetic field, and the heat transfer process. The ferromagnetic gold nanoparticles (AuNPs) exhibit diverse shapes (bricks, cylinders, and platelets) and possess both magnetic and thermal attributes thereby enhancing the efficiency of heat transfer process. The peristaltic thrust drives the dynamic behavior of the gold blood nanofluid through a compliant tube. The tube walls are flexible and exhibit a curvature effects that can alter the dynamics of fluid flow. The effective Hamilton‐Crosser model is selected to express the thermal conductivity of the nanofluid. Gold blood nanofluids can be treated as incompressible, non‐Newtonian, and MHD fluid flow. The governing equations of the system are solved using the perturbation approach under the assumptions of low Reynolds numbers and long wavelength. Hybrid interactions of magnetic field, radiative heating, thermal slip, elastic wall properties, and gold nanoparticles shapes and concentrations are investigated within the gold blood nanofluid flow. The resulting graphs include the profiles of velocity, temperature distributions, EG, and irreversibility parameters under the influence of the above parameters. The findings reveal that the overall EG rises with increasing values of heat source intensity, Brinkman number, temperature difference factor, compliant wall curvature coefficient, and gold nanoparticles concentrations. Additionally, it is observed that an increase in magnetic flux strength results in the emergence of reversal flow patterns near the walls. This arises due to the augmented magnetic flux obstructing the peristaltic nanofluid flow leading to reduce streamwise velocity. Moreover, heightened magnetic flux strength causes temperature reduction for both thermal slip and non‐slip conditions. Generally, the presence of a thermal slipping parameter further enhances the distribution of temperature. In essence, the rationale and significance of this study primarily revolve around comprehending the interplay of these diverse factors with MHD peristaltic motion of gold blood nanofluid and EG. This not only furthers our theoretical understanding of complex systems but also has practical implications that can improve new technologies, processes, and medical applications. For example, in medical treatments like photothermal therapy (PPT), insights gained from this research can help in developing more effective and precise treatment methods. By understanding the impact of these factors on EG, new ways can be identified to minimize or manage system inefficiencies leading to more sustainable and optimized treatment processes. This research holds promise for application in cancer detection and treatment by employing a combination of PPT and magnetic hyperthermia. This entails dispersing AuNPs into the blood circulation through arteries and blood vessels and subsequently applying photothermal radiation and a magnetic field.
With the growing demand for energy supply and the natural decline of oil reservoirs, the development of new enhanced oil recovery (EOR) techniques become more and more critical. Polymer flooding EOR is one of the most successful chemical EOR methods but suffers many drawbacks at high temperatures and high salinity (HT‐HS) conditions. Superparamagnetic nanoparticles (NPs) have been recently investigated for subsurface applications, including in EOR, due to their unique physicochemical properties. Their applicability under harsh reservoir conditions, however, is yet to be examined. In this work, a novel approach is developed to synthesize superparamagnetic Fe3O4 (NPs) with unique surface functionalization (SMag‐NPs) and to form stable polyacrylamide (PAM) dispersions (SMag‐NPs‐PAM). Both stability and core flooding experiment results demonstrate the promising future of the new dispersion. The SMag‐NPs‐PAM dispersion is not only stable at HT‐HS conditions, but also show excellent EOR capability at HT‐HS by recovering, 61.72% of the initial oil quantity, which is significantly higher than those from conventinal NPs‐PAM disperison and pure PAM fluid. These findings show the promising application potential of SMag‐NPs‐PAM for improving oil recovery in challenging HT‐HS reservoir conditions.
Nanoparticles have recently attracted huge attention as an engineering alternative in various fields. This is not unconnected with its established ability to perform better when used to replace some conventional systems or used as an enhancement for the system. Hence, this study reviewed the viability of nanofluids developed from nanoparticles as a possible replacement for conventional refrigerants available. In this review, focus was placed on refrigerants and refrigeration types, Nanoparticles and Nanofluids, Synthesis, Characterization and properties of Nanoparticles and finally on Nano-refrigerants and their viability. Conclusions were reached based on findings of the review.
Micromixers are devices used for mixing fluids at the microscale level and are used for a variety of applications, including chemical reactions, mass transport, and heat transfer processes. In heat transfer processes, micromixers can enhance the heat transfer rate by creating a more homogeneous fluid mixture. In this research, the flow and heat transfer of a nanofluid are simulated in four different geometry of micromixers. The objective is to investigate which one has a better performance compared to a smooth microchannel with regard to the performance evaluation criterion (PEC), which proposes an evaluation with regard to the trade-off between heat transfer and pressure drop. For this purpose, the Ag/water nanofluid is simulated in micromixers of different geometries at Re numbers ranging from 200 to 800 and solid volume fractions (SVF) of 0, 2, and 4% using a finite volume method. The mixture model is adopted to simulate the nanofluid as a two-phase fluid, which is subjected to a laminar flow regime. The micromixers’ walls are exposed to constant heat flux. The effect of increasing the Re number and the SVF is assessed and compared in all geometries, and the results indicate that an increase in both these figures increases the PEC considerably. Moreover, the PEC for each case is assessed and compared, and the best and worst geometry in terms of heat transfer as well as pressure drop are presented. Specifically, in the best case with the highest PEC at the Re = 800 and SVF = 4%, the Nu number is increased by 2.3 fold while its pressure drop is increased by 1.42 fold compared to a smooth microchannel.
The present paper deals with a comprehensive experimental study of the hysteresis phenomenon of alumina-water based nanofluids taking place during heating-cooling cycles. The emphasis was particularly put on the relationship between this phenomenon and the dispersion state of alumina nanoparticles. Thus, by carrying out simultaneous thermal conductivity and dynamic viscosity measurements, five dispersion regimes were highlighted. The influence of the temperature on these two properties as well as the pH of the solution was then investigated for six characteristic conditions in the well-dispersed and chain-like agglomerated regimes and for temperatures between 20 and 80 °C. The results evidenced that as long as the temperature, and as a consequence the pH, does not exceed a critical value, no hysteresis phenomenon occurs during the heating and cooling processes. Eventually, it was found out that this critical temperature is strongly dependent on the dispersion regime and the initial pH of the nanofluid.
Viscosity is a crucial rheological property essential in predicting the behaviour of any fluid. It is vital to expect the fluid flow trend in various processes. This paper surveys multiple methods to find the viscosity of liquefied metals and different fluids. These methods include capillary, oscillating, rotational, draining vessels, etc. Several models are surveyed that can estimate the viscosity of fluids. The temperature dependency of viscosity is also provided. The paper includes various devices based on different working principles and correlations proposed by multiple authors for determining the viscosity of fluids. The article helps the researchers select the appropriate viscometer, method, and correlation to estimate their research's fluid viscosity.
In this paper, the last experimental results of the thermal conductivity of nanofluids
have been investigated; therefore, because of the enormous numbers or some
repetitions of such studies, it just tried to focus on those which had more acceptable
results; however, it is not intended to present a systematic summary of the available
references from the literature. All kinds of nanoparticles such as Al2O3, Fe3O4, TiO2,
and CuO and their base-fluids such as water, Engine Oil, Glycol, Ethylene Glycol, and
others have been investigated. The results showed that the effect of particle size of
nanoparticle has a reversed impact on the value of thermal conductivity. To clarify, the
thermal conductivity could increase by reduction in size of nanoparticles. On the other
hand, the lower the suspension volume fraction is, the higher the thermal conductivity
will be in non-linear relation. Also the thermal conductivity and the temperature of the
suspension have the direct influence on each other. In addition to the fact that a review
paper has been prepared, the belief is to start this research with the scientific
classification in order of all terms and expressions which have been used by previous
scholars.
This article investigates the influence of temperature, concentration, and size of nanoparticles, and addition of surfactants on dynamic viscosity of water-based nanofluids containing alumina (Al2O3) and titania (TiO2) nanoparticles. Two viscometers, a capillary and a falling ball, were used for the measurements in the temperature range of 20-50 °C and the particle concentration of 3-14.3 wt.%. The results indicate that the viscosity of nanofluids is reduced by increasing the temperature, similar to their base fluids. Moreover, surfactants, which are used to improve the shelf stability of nanofluids, most likely increase their viscosity. The correlations derived from the linear fluid theory such as Einstein and Batchelor, especially for solid concentration above 1.5 wt.% are not accurate to predict viscosity of nanofluids, while the modified Krieger-Dougherty equation estimates viscosity of nanofluids with acceptable accuracy in a specific range of solid particle size to aggregate size.
Since the past decade, rapid development in nanotechnology has produced several aspects for the scientists
and technologists to look into. Nanofluid is one of the incredible outcomes of such advancement. Nanofluids
(colloidal suspensions of metallic and nonmetallic nanoparticles in conventional base fluids) are best known for
their remarkable change to enhanced heat transfer abilities.Earlier research work has already acutely focused on thermal conductivity of nanofluids. However, viscosity is another important property that needs the same attention due to its very crucial impact on heat transfer. Therefore, viscosity of nanofluids should be thoroughly investigated before use for practical heat transfer applications. In this contribution, a brief review on theoretical models is presented precisely. Furthermore, the effects of nanoparticles’ shape and size, temperature, volume concentration, pH, etc. are organized together and reviewed.
In modern science and engineering nanofluids are playing a vital role in the application of heat transfer devices due to their effective properties. Addition of nanoparticles in the fluid can alter thermophysical properties of the nanofluid. Experimental and theoretical studies are essential to understand the change in fluid dynamics aspects of the fluid by the addition of nanoparticles. This paper presents a brief review on the viscous and thermal transport effects of nanofluids. The main emphasis is on the comparison of previous theoretical and experimental studies for thermophysical properties of nanofluids. These properties include density, viscosity, thermal conductivity and specific heat capacity of nanofluids.
In this work nanofluids have been prepared by dispersing Al2O3 nanoparticles in different base fluids such as 20:80%, 40:60% and 60:40% by weight of ethylene glycol (EG) and water (W) mixtures. Thermal conductivity and viscosity experiments have been conducted in temperatures between 20 °C and 60 °C and in volume concentrations between 0.3% and 1.5%. Results indicate that thermal conductivity of nanofluids increases with increase of volume concentrations and temperatures. Similarly, viscosity of nanofluid increases with increase of volume concentrations but decreases with increase of temperatures. Among all the nanofluids maximum thermal conductivity enhancement was observed for 20:80% EG/W nanofluid about 32.26% in the volume concentration of 1.5% at a temperature of 60 °C. In a similar way among all the nanofluids maximum viscosity enhancement was observed for 60:40% EG/W nanofluid about 2.58-times in the volume concentration of 1.5% at a temperature of 0 °C. The classical Hamilton–Crosser and Einstein models failed to predict the thermal conductivity and viscosity of nanofluids with influence of temperatures. Hence correlations have been proposed for the estimation of thermal conductivity and viscosity of nanofluids. The potential heat transfer benefits of nanofluids in laminar and turbulent flow conditions have been explained for conditions of fixed mass flow rate and geometry.
This study investigates the fabrication, thermal conductivity and rheological characteristics evaluation of nanofluids consisting of copper nanoparticles in diethylene glycol base liquid. The fabricated Cu nanofluids displayed enhanced thermal conductivity over the base liquid. Copper nanoparticles were directly formed in diethylene glycol using microwave-assisted heating, which provides uniform heating of reagents and solvent, accelerating the nucleation of metal clusters, resulting in monodispersed nanostructures. Copper nanoparticles displayed an average primary particle size of 75 ± 25 nm from SEM micrographs, yet aggregated to form large spherical particles of about 300 nm. The physicochemical properties including thermal conductivity and viscosity of nanofluids were measured for the nanofluids with nanoparticle concentration between 0.4 wt% and 1.6 in the temperature range of 20–50 °C. Proper theoretical correlations/models were applied to compare the experimental results with the estimated values for thermal conductivity and viscosity of nanofluids. For all cases, thermal conductivity enhancement was higher than the increase in viscosity showing the potential of nanofluids to be utilized as coolant in heat transfer applications. A thermal conductivity enhancement of ∼7.2% was obtained for nanofluids with 1.6 wt% nanoparticles while maximum increase in viscosity of ∼5.2% was observed for the same nanofluid.
Nanofluids have drawn large attention because they exhibit anomalous behaviour in their thermo physical properties. There has been an enormous innovation in heat transfer applications of these fluids especially to industrial sectors including transportation, power generation, cooling, thermal therapy for cancer treatment, etc. In the present work, we have studied the anomalous increase in the thermal conductivity and viscosity of nanofluids by taking clustering as one of the causes. It is assumed that the nanoparticles may aggregate on dispersion. Few of these nanoparticles may just touch each other, whereas others may do so along with interfacial layer developed around them (analogous to porous media). The variation in thermal conductivity has been studied with particle concentration, concentration of aggregates and thickness of interfacial layer. The concept of aggregation and equivalent volume fraction has also been used in Kreiger and Dougherty (K-D) model to study the viscosity of nanofluids. The obtained results for thermal conductivity agree well with the available experimental results when the effect of different types of clusters is taken into account. Viscosity increases with the increase in particle aggregate (r
a) and is found to match well for r
a = 3r at low concentration.
This article reports viscosity data on a series of colloidal dispersions collected as part of the International Nanofluid Property Benchmark Exercise (INPBE). Data are reported for seven different fluids that include dispersions of metal-oxide nanoparticles in water, and in synthetic oil. These fluids, which are also referred to as ‘nanofluids,’ are currently being researched for their potential to function as heat transfer fluids. In a recently published paperfrom the INPBE study, thermal conductivity data from more than 30 laboratories around the world were reported and analyzed. Here, we examine the influence of particle shape and concentration on the viscosity of these same nanofluids and compare data to predictions from classical theories on suspension rheology.
Nanofluids attract researchers in many ways for its enhanced heat transfer properties. Nanorefrigerant is one kind of nanofluids. It has better heat transfer performance than traditional refrigerants. Recently, some experiments have been done about nanorefrigerant, which are mostly related to heat transfer performance of these fluids. Thermal conductivity, viscosity and density are the basic thermophysical properties that must be analyzed before performance analysis. In this paper, the volumetric effects of thermal conductivity, viscosity and density of Al2O3/R141b nanorefrigerant have been studied for different temperature ranges. Based on the analysis about nanorefrigerant it is found that, thermal conductivity increases with the increase of volume concentrations and temperatures. However, viscosity and density increases accordingly with the enhancement of volume concentrations and decreases with the increase of temperature. As, heat transfer performances increases with the augmentation of thermal conductivity and pressure drop and pumping power increases with the enhancement of viscosity and density. Therefore, an optimum volume concentration of nanorefrigerant could improve the performance of a refrigeration system.
The 12 papers i nthis special section focus on measurement techniques and fundamental applications.
Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in many industrial applications. In this paper we propose that an innovative new class of heat transfer fluids can be engineered by suspending metallic nanoparticles in conventional heat transfer fluids. The resulting {open_quotes}nanofluids{close_quotes} are expected to exhibit high thermal conductivities compared to those of currently used heat transfer fluids, and they represent the best hope for enhancement of heat transfer. The results of a theoretical study of the thermal conductivity of nanofluids with copper nanophase materials are presented, the potential benefits of the fluids are estimated, and it is shown that one of the benefits of nanofluids will be dramatic reductions in heat exchanger pumping power.
The effects due to temperature and shearing time on viscosity for Al2O3/water and CNT/water based nanofluids at low concentration and low temperatures are experimentally investigated. The viscosity data were collected using a stress-controlled rheometer equipped with parallel plate geometry under up and down shear stress ramp. CNT and Al2O3 water based nanofluids exhibited hysteresis behaviour when the stress is gradually loaded and unloaded, depending also on shearing time. Experiments also showed that the nanofluid suspensions indicated either Newtonian or non-Newtonian behaviour, depending on shear rate. CNT water based nanofluid behaves as Newtonian fluid at high shear rate whereas Al2O3 water based nanofluid is non-Newtonian within the range of low temperatures investigated.
Nanorefrigerant is one kind of nanofluids. It is the mixture of nanoparticles with refrigerants. It has better heat transfer performance than traditional refrigerants. Recently, some researches have been done about nanorefrigerants. Most of them are related to thermal conductivity of these fluids. Viscosity also deserves as much consideration as thermal conductivity. Pumping power and pressure drop depends on viscosity. In this paper, the volumetric and temperature effects over viscosity of R123-TiO 2 nanorefrigerants have been studied for 5 to 20°C temperature and up to 2 vol. %. The effect of pressure drop with the increase of viscosity has also been investigated. Based on the analysis it is found that viscosity of nanorefrigerant increased accordingly with the increase of nanoparticle volume concentrations and decreases with the increment of temperature. Furthermore, pressure drop augmented significantly with the intensification of volume concentrations and vapor quality. Therefore, low volume concentrations of nanorefrigerant are suggested for better performance of a refrigeration system.
Nanorefrigerant is one kind of nanofluids that seems to be possessing better heat transfer performance over traditional refrigerants. Viscosity is an important thermo physical property of the refrigeration which affects its performance. Our investigation is done on viscosity of Al 2 O 3 –R11 nanorefrigerant at different nanoparticle concentrations and temperature. Al 2 O 3 (20nm) nanoparticles are mixed with the refrigerant R-11 at varying concentration (0.01-0.05 vol %) using ultrasonic vibration. The objective of this study is to investigate the dependence of viscosity of Al 2 O 3 –R11 nanorefrigerant on temperature (4-16 0 C) at different volume concentrations. Based on the experimental analysis it is found that viscosity augmented significantly with the increase of volume concentrations. Therefore, low volume concentration (upto0.03%) of nano-refrigerant can improve the performance of a refrigeration system in the temperature range from 4-16 0 C.
In this study, the effect off adding SiO2 nanoparticles on the viscosity of base fluid is investigated experimentally. Base fluids are chosen among common heat transfer fluids such as ethylene glycol, transformer oil and water. In addition different volume percentages of ethylene glycol in water are used as ethylene glycol-water solution. In every base fluid different volume fractions of SiO2 nanoparticles is added. It is shown that the viscosity of solution enhance by adding nanoparticles. The effect of cooling and heating process on the viscosity of nanofluid is also discussed. The presented data show that as the temperature increases the viscosity of base fluid and nanofluid decrease. It is also revealed that there are very little differences between the viscosity of nanofluid in a specific temperature at cooling and heating cycles. According to the experimental results new correlations for predicting the viscosity of nanofluids is presented. These correlations relate the viscosity of nanofluid to the particle volume fraction and temperature.
Utilizing nanofluids as an advanced kind of liquid mixture with a small concentration of nanometer-sized solid particles in suspension is a relatively new field, which is less than two decades old. The aim of this review paper is the investigation of the nanofluids’ applications in solar thermal engineering systems. The shortage of fossil fuels and environmental considerations motivated the researchers to use alternative energy sources such as solar energy. Therefore, it is essential to enhance the efficiency and performance of the solar thermal systems. Nearly all of the former works conducted on the applications of nanofluids in solar energy is regarding their applications in collectors and solar water heaters. Therefore, a major part of this review paper allocated to the effects of nanofluids on the performance of solar collectors and solar water heaters from the efficiency, economic and environmental considerations viewpoints. In addition, some reported works on the applications of nanofluids in thermal energy storage, solar cells, and solar stills are reviewed. Subsequently, some suggestions are made to use the nanofluids in different solar thermal systems such as photovoltaic/thermal systems, solar ponds, solar thermoelectric cells, and so on. Finally, the challenges of using nanofluids in solar energy devices are discussed.
The development and use of nanofluids, i.e., dilute suspensions of nanoparticles in liquids, have found a wide range of applications in consumer products, nanomedicine, energy conversion, and microsystem cooling. Of special interest is the use of nanofluid flow for enhanced convection heat transfer to achieve rapid cooling of high heat-flux devices. However, for proper optimization of such thermal engineering systems in terms of design and operation, not only the heat transfer has to be maximized but the entropy generation has to be minimized as well. In this paper, theoretical and computational contributions on entropy generation due to flow and heat transfer of nanofluids in different geometries and flow regimes are reviewed. First, a variety of models used to calculate the thermophysical properties of nanofluids are presented. Then, the effects of thermal nanofluid flow on the rate of entropy generation for different applications are discussed. Finally, some suggestions for future work are presented. The aim of this review paper is to motivate the researchers to pay more attention to the entropy generation analysis of heat and fluid flow of nanofluids to improve the system performance.
The viscosity and thermal conductivity of ZnO nanofluids with nanoparticle shapes of nearly rectangular and of sphere, were experimentally investigated under various volume concentrations of the nanoparticles, ranging from 0.05 to 5.0 vol.%. The viscosity of the nanofluids increased with increases in the volume concentration by up to 69%. In addition, the enhancement of the viscosity of the nearly rectangular shape nanoparticles was found to be greater by 7.7%, than that of the spherical nanoparticles. The thermal conductivity of the ZnO nanofluids increased by up to 12% and 18% at 5.0 vol.% for the spherical and the nearly rectangular shape nanoparticles, respectively, compared to that of the base fluid (water). The shape of the particles is found to have a significant effect on the viscosity and thermal conductivity enhancements.
In this article, the viscosity of two common nanofluids including Al2O3/water and TiO2/water is measured at high temperatures, and high concentrations of the nanofluids. The range of temperature is 15–60°C where the volume fraction of nanoparticles varies from 1 to 8%. Next, comparisons have been done with the most well-known theoretical and experimental reports in the literature. Finally, using the experimental data, a helpful correlation is presented.
A considerable number of studies can be found on the thermal conductivity of nanofluids in which Al2O3 nanoparticles are used as additives. In the present study, the aim is to measure the thermal conductivity of very narrow Al2O3 nanoparticles with the size of 5 nm suspended in water. The thermal conductivity of nanofluids with concentrations up to 5 % is measured in a temperature range between 26 and 55 °C. Using the experimental data, a correlation is presented as a function of the temperature and volume fraction of nanoparticles. Finally, a sensitivity analysis is performed to assess the sensitivity of thermal conductivity of nanofluids to increase the particle loading at different temperatures. The sensitivity analysis reveals that at a given concentration, the sensitivity of thermal conductivity to particle loading increases when the temperature increases.
Experimental measurements of the viscosity of molten salts nanofluid containing multi-walled carbon nanotubes were performed for a wide range of the shear rate and various nanotube concentrations. In addition, the effect of nanoparticle aggregation is also investigated in the present study. The high temperature nanofluid showed the non-Newtonian behavior in low shear rate region but it was extended to high shear rate region by increasing the nanoparticle concentration. The viscosity of the nanofluid is significantly enhanced up to 93% in the concentration of 2 wt%. The results are well matched with the Krieger-Dougherty equation using a nanoparticle aggregation factor.
This paper is a continuation of the authors' previous work on the thermophysical properties, heat transfer, and pressure drop of nanofluids [Experimental Thermal and Fluid Science 52 (2014) 68–78]. In this paper, an experimental study is carried out to study the turbulent flow of COOH-functionalized multi-walled carbon nanotubes/water nanofluid flowing through a double tube heat exchanger. For this purpose, first, the thermophysical properties of the nanofluid, including the thermal conductivity and dynamic viscosity, have been measured at various temperatures and concentrations. Using the measured data, new correlations as a function of temperature and concentration are presented to predict the thermophysical properties. In the next step, the effects of low volume fractions of the nanofluid (from 0.05% to 1%) on the heat transfer rate are studied at the Reynolds numbers between 5000 and 27,000. The experimental results reveal that with increasing the nanofluid concentration, the heat transfer coefficient and thermal performance factor increase. On average, a 78% increase in heat transfer coefficient, a 36.5% increase in the average Nusselt number, and a 27.3% penalty in the pressure drop are recorded for the highest concentration of MWCNTs in water.
In this paper, an analytical analysis has been performed to evaluate the performance of a minichannel-based solar collector using four different nanofluids including Cu/water, Al2O3/water, TiO2/water, and SiO2/water. The analysis of first and second laws is conducted for turbulent flow by considering the constant mass flow rate of nanofluid. The results are presented for volume fractions up to 4% and nanoparticle size of 25 nm where the inner diameter of the risers of flat plate collector is assumed to be 2 mm. Analysis of the first law of thermodynamics reveals that Al2O3/water nanofluids show the highest heat transfer coefficient in the tubes while the lowest value belongs to SiO2/water nanofluids. The highest outlet temperature is provided by Cu/water nanofluids, and after that TiO2/water, Al2O3/water, and SiO2/water nanofluids are in ranks of second to fourth. The results of second law analysis elucidate that Cu/water nanofluid produces the lowest entropy generation among the nanofluids. It is found that although the effective thermal conductivity of TiO2/water nanofluids is less than Al2O3/water nanofluids, but the entropy generation of TiO2/water is lower than Al2O3/water. Finally, some recommendations are given for future studies on the applications of nanofluids in solar collectors.
The rheological characteristics of ZnO–propylene glycol nanofluid have been studied over a temperature range of 10–140 °C and nanoparticle concentration range of 0–2 vol%. The addition of ZnO nanoparticles (35–40 nm) to propylene glycol (PG) weakens the inter-molecular hydrogen bonding in propylene glycol. This is reflected in the reduced values of viscosity for nanoparticle dispersions (nanofluids) compared to that of base fluid. The viscosity decrease is more pronounced at lower temperatures and at higher nanoparticle concentration. The percentage reduction in viscosity is 53 and 32 % at 10 and 28 °C, respectively, for 2 vol% ZnO–propylene glycol nanofluid compared to pure PG. This dispersion has immense potential for cooling application owing to lower viscosity. At high temperatures where the hydrogen bonds in the base fluid are substantially weaker, viscosity of ZnO–PG dispersions is higher than that of PG. An estimated 80 and 37 % enhancement in heat transfer coefficient can be achieved using 2 vol% ZnO–PG nanofluid at temperatures of 10 and 28 °C, respectively.
A numerical investigation has been carried out applying single phase approach on turbulent forced convection flow of water based Al2O3 and TiO2 nanofluids flowing through a horizontal circular pipe under uniform heat flux boundary condition applied to the wall. The effect of volume concentrations, Brownian motion and size diameter of nanoparticles on flow and heat transfer have been examined for Reynolds number, Re = 10 × 103 to 100 × 103, Prandtl number, Pr = 7.04 to 20.29, nanoparticle volume concentration, χ = 4% and 6% and nanoparticles size diameter, dp = 10, 20, 30 and 40 nm respectively. Results reveal that the small size of nanoparticles with their Brownian motion has the highest average shear stress ratio, heat transfer rate and thermal performance factor for χ = 6%. Besides, it is found that the heat transfer rate increases as the particle volume concentration and Reynolds number increase with a decrease of nanoparticles size diameter. Moreover, Al2O3 water nanofluid shows a higher heat transfer rate compared to that of TiO2–water nanofluid. Finally, a conclusion has been drawn from the present analysis that the heat transfer performance is more affected by the size diameter and Brownian motion of nanoparticles than the thermal conductivity of nanofluid. Results of the non-dimensional fully developed velocity and turbulent kinetic energy, frictional factor and average Nusselt number for pure fluid (water) as well as the result of average Nusselt number for Al2O3 and TiO2–water nanofluid have been validated with published experimental results as well as with available correlations where a reasonable good agreement has been achieved.
Experimental studies are performed to evaluate the stability of zinc oxide (ZnO) nanoparticles suspended in a mixture of ethylene glycol and water with weight ratio of 40–60 as the base fluid. Different methods have been employed to disperse ZnO nanoparticles. It is found that using Gum Arabic leads to clustering and settle the nanoparticles. Also, the use of DI ammonium hydrogen citrate with weight ratio 1:1 (surfactant:nanoparticles) gives the acceptable stability. The density of nanofluids is measured and the results are compared with theoretical results. A helpful correlation for the measured densities of the stable nanofluids in a temperature range of 25–40 °C is presented which can used in practical applications. Finally based on the correlation a sensitivity analysis has been done. It is found that at higher temperatures the density is more sensitive to the increases in volume fraction.
Nanofluids consisting of nanoparticles dispersed in heat transfer carrier fluid have received attention over the last view years for their enormous potential to improve the efficiency of heat transfer fluids. This work investigated the synthesis of ZnO nanoparticle-based thermal fluids prepared using a two-step process. Chemical precipitation was used for the synthesis of the ZnO powders, and ultrasonic irradiation was used to disperse the nanoparticles in ethylene glycol as the base fluid. The thermal conductivity enhancement of the nanofluid demonstrated a nonlinear relationship with respect to volume fraction and crystallite size, with increases in the volume fraction and crystallite size both resulting in increases in the measured enhancement. The nanofluids used in conductivity measurements were further employed as the working medium for a conventional screen-mesh wick heat pipe. The experiments were performed to measure the temperature distribution and thermal resistance of the heat pipe. The results showed temperature distribution and thermal resistance to decrease as the concentration and the crystallite size of the nanoparticle increased.
Experimental investigations are performed to determine the viscosity of TiO2 and Al2O3 nanoparticles suspended in a mixture of ethylene glycol/water (EG–water, 20/80 wt%). The experiments are conducted at various volume fractions between 0% and 4% and a temperature range of 15–60 °C. Some comparisons are made between the experimental results and the theoretical models and correlations presented for viscosity in the literature. The results indicate that the theoretical models are not suitable to predict the viscosity of nanofluids. Finally, using the experimental data, a useful correlation is presented to predict the viscosity. To estimate the required pumping power in an energy device, in the first, the viscosity should be determined. Therefore, the results of the present work may be helpful in the design of energy devices.
In order to obtain a novel thermo-fluid with both turbulent drag reducing and heat transfer enhancement (compared with drag-reduced flow) abilities, we have prepared a viscoelastic-fluid-based nanofluid (VFBN) using viscoelastic aqueous solution of cetyltrimethyl ammonium chloride/sodium salicylate as base fluid and multiwalled carbon nanotubes (MWCNTs) as nanoparticles. The thermal conductivity and shear viscosity of the prepared VFBN with various particle volume fractions, temperatures and concentrations of the base fluid were then experimentally investigated. The results show that thermal conductivities of the tested VFBNs are significantly higher than that of the corresponding base fluid and increase with increasing particle volume fraction and fluid temperature, demonstrating potentials in heat transfer enhancement. A modified Li–Qu–Feng model (Y.H. Li, W. Qu, J.C. Feng, Chinese Phys. Lett. 25 (2008) 3319–3322), which includes the effect of liquid layering, particle clustering, particle shape factor, Brownian motion and viscosity of base fluid, is proposed in the present paper to predict thermal conductivity of VFBNs containing MWCNTs. The results predicted by this modified Li–Qu–Feng model show excellent agreements with the measured data. The VFBN with MWCNTs shows a non-Newtonian fluid behavior in its shear viscosity, and its shear viscosity increases with the increase of particle volume fraction and decrease of temperature. It is expectable that the prepared VFBNs may also have drag-reducing ability in turbulent flows.
Thermal conductivity, viscosity and heat transfer coefficient of water-based alumina and titania nanofluids have been investigated. The thermal conductivity of alumina nanofluids follow the prediction of Maxwell model, whilst that of titania nanofluids is slightly lower than model prediction because of high concentration of stabilisers. None of investigated nanofluids show anomalously high thermal conductivity enhancement frequently reported in literature. The viscosity of alumina and titania nanofluids was higher than the prediction of Einstein–Batchelor model due to aggregation. Heat transfer coefficients measured in nanofluids flowing through the straight pipes are in a very good agreement with heat transfer coefficients predicted from classical correlation developed for simple fluids. Experimental heat transfer coefficients in both nanofluids as well as corresponding wall temperatures agree within ±10% with the values obtained from numerical simulations employing homogeneous flow model with effective thermo-physical properties of nanofluids. These results clearly shows that titania and alumina nano-fluids do not show unusual enhancement of thermal conductivity nor heat transfer coefficients in pipe flow frequently reported in literature.
Nanofluids are nanotechnology-based colloidal dispersions engineered by stably suspending nanoparticles. Transmission electron microscopy and scanning electron microscope images are acquired to characterize the shape and size of SiC nanoparticles, because the properties of the nanofluids depend on the morphologies of nanoparticles. The dispersion behavior for SiC/deionized water (DIW) nanofluids were investigated under different pH values and characterized with the zeta potential values. The isoelectric point of SiC/DIW nanofluid was identified in terms of colloidal stability. Then their viscosity and thermal conductivity were investigated as a function of volume fraction to evaluate SiC/DIW nanofluids’ potential to function as more effective working fluids in heat transfer applications.
An asymptotic technique is used to derive the functional dependence of effective viscosity on concentration for a suspension of uniform solid spheres, in the limit as concentration approaches its maximum value. This result, containing no empirical constants, is intended to complement the classical Einstein formula which is valid only at infinite dilution. Good agreement is found between the asymptotic solution and available data, provided that the maximum concentration is determined from the data themselves.RésuméUne technique asymptotique est employée pour déduire la dépendence fonctionnelle de la viscosité effective de la concentration pour une suspension de sphères uniformes solides à la limite quand la concentration se rapproche de sa valeur maximum. Ce résultat, ne contenant aucune constante enpirique, est compris comme complément de la formule classique d'Einstein qui est seulement valable pour une dilution infinie. On trouve un accord satisfaisant entre la solution asymptotique et les données disponibles à condition que la concentration maximum soit déterminée à partir des données elles-mêmes.ZusammenfassungZum Ableiten der funktionellen Abhängigkeit der effektiven Viskosität von der Konzentration in einer Suspension gleichförmiger, fester Kugeln—innerhalb des Bereiches, in dem sich die Konzentration ihrem Höchstwert nähert—wird eine asymptotische Technik angewandt. Das Ergebnis, das keine empirischen Konstanten enthält, soll die klassische Einsteinformel ergänzen, die nur in unendlicher Verdünnung gilt. Zwischen der asymptotischen Lösung und den zur Verfügung stehenden Daten wurde gute Übereinstimmung gefunden, vorausgesetzt, dass die Höchstkonzentration aus diesen Daten selbst bestimmt wird.
A procedure for preparing a nanofluid that a solid-liquid composite material consists of solid nanoparticles with sizes typically
of 1–100 nm suspended in liquid was proposed. By means of the procedure, Cu-H2O nanofluids with and without dispersant were prepared, whose sediment photographs and particle size distribution were given
to illustrate the stability and evenness of suspension with dispersant. The viscosity of Cu-H2O nanofluid was measured using capillary viscometers. The mass fractions(w) of copper nanoparticles in the experiment varied between 0.04% and 0.16% with the temperature range of 30–70 °C. The experimental
results show that the temperature and SDBS concentration are the major factors affecting the viscosity of the nano-copper
suspensions, while the effect of the mass fraction of Cu on the viscosity is not as obvious as that of the temperature and
SDBS dispersant for the mass fraction chosen in the experiment. The apparent viscosity of the copper nano-suspensions decreases
with the temperature increase, and increases slightly with the increase of the mass fraction of SDBS dispersant, and almost
keeps invariability with increasing the mass fraction of Cu. The influence of SDBS concentration on the viscosity of nano-suspension
was relatively large comparing with that of the nanoparticle concentration.
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A generalized equation is proposed for the relative elastic moduli of composite materials. By the introduction of a generalized Einstein coefficient and a function which considers the maximum volumetric peaking fraction of the filler phase, the moduli of many types of composite systems can be calculated.
An expression for the viscosity of solutions and suspensions of finite concentration is derived by considering the effect of the addition of one solute‐molecule to an existing solution, which is considered as a continuous medium.
The past decade has seen the rapid development of nanofluids science in many aspects. Number of research is conducted that is mostly focused on the thermal conductivity of these fluids. However, nanofluid viscosity also deserves the same attention as thermal conductivity. In this paper, different characteristics of viscosity of nanofluids including nanofluid preparation methods, temperature, particle size and shape, and volume fraction effects are thoroughly compiled and reviewed. Furthermore, a precise review on theoretical models/correlations of conventional models related to nanofluid viscosity is presented. The existing experimental results about the nanofluids viscosity show clearly that viscosity augmented accordingly with an increase of volume concentration and decreased with the temperature rise. However, there are some contradictory results on the effects of temperature on viscosity. Moreover, it is shown that particle size has some noteworthy effects over viscosity of nanofluids.
This work focuses on the study of natural convection heat transfer characteristics in a differentially-heated enclosure filled with a CuO–EG–Water nanofluid for different published variable thermal conductivity and variable viscosity models. The problem is given in terms of the vorticity–stream function formulation and the resulting governing equations are solved numerically using an efficient finite-volume method. Comparisons with previously published work are performed and the results are found to be in good agreement. Various results for the streamline and isotherm contours as well as the local and average Nusselt numbers are presented for a wide range of Rayleigh numbers (Ra = 103–105), volume fractions of nanoparticles (0 ≤ φ ≤ 6%), and enclosure aspect ratios (½ ≤ A ≤ 2). Different behaviors (enhancement or deterioration) are predicted in the average Nusselt number as the volume fraction of nanoparticles increases depending on the combination of CuO–EG–Water variable thermal conductivity and viscosity models employed. In general, the effects the viscosity models are predicted to be more predominant on the behavior of the average Nusselt number than the influence of the thermal conductivity models. The enclosure aspect ratio is predicted to have significant effects on the behavior of the average Nusselt number which decreases as the enclosure aspect ratio increases.
Stokes flow through a random, moderately dense bed of spheres is treated by a generalization of Brinkman's (1947) method, which is applicable to both stationary beds and suspensions. For stationary beds, Darcy's law with a permeability result similar to Brinkman's is derived. For suspensions an effective viscosity μ/(1–2·60ψ) is found, where ψ is the volume fraction of spheres. Also, an expression for the settling velocity is derived.
The effect of Brownian motion of particles in a statistically homogeneous suspension is to tend to make uniform the joint probability density functions for the relative positions of particles, in opposition to the tendency of a deforming motion of the suspension to make some particle configurations more common. This smoothing process of Brownian motion can be represented by the action of coupled or interactive steady ‘thermodynamic’ forces on the particles, which have two effects relevant to the bulk stress in the suspension. Firstly, the system of thermodynamic forces on particles makes a direct contribution to the bulk stress; and, secondly, thermodynamic forces change the statistical properties of the relative positions of particles and so affect the bulk stress indirectly. These two effects are analysed for a suspension of rigid spherical particles. In the case of a dilute suspension both the direct and indirect contributions to the bulk stress due to Brownian motion are of order ø2, where ø([double less-than sign] 1) is the volume fraction of the particles, and an explicit expression for this leading approximation is constructed in terms of hydrodynamic interactions between pairs of particles. The differential equation representing the effects of the bulk deforming motion and the Brownian motion on the probability density of the separation vector of particle pairs in a dilute suspension is also investigated, and is solved numerically for the case of relatively strong Brownian motion. The suspension has approximately isotropic structure in this case, regardless of the nature of the bulk flow, and the effective viscosity representing the stress system to order φ2 is found to be
\[
\mu^{*} = \mu(1+2.5\phi + 6.2\phi^2).
\]
The value of the coefficient of ø2 for steady pure straining motion in the case of weak Brownian motion is known to be 7[cdot B: small middle dot]6, which indicates a small degree of ‘strain thickening’ in the ø2-term.
In this paper a new equation for calculating the nanofluid viscosity by considering the Brownian motion of nanoparticles is introduced. The relative velocity between the base fluid and nanoparticles has been taken into account. This equation presents the nanofluid viscosity as a function of the temperature, the mean nanoparticle diameter, the nanoparticle volume fraction, the nanoparticle density and the base fluid physical properties. In developing the model a correction factor is introduced to take into account the simplification that was applied on the boundary condition. It is calculated by using very limited experimental data for nanofluids consisting of 13 nm Al2O3 nanoparticles and water and 28 nm Al2O3 nanoparticles and water. The predicted results are then compared with many other published experimental results for different nanofluids and very good concordance between these results is observed. Compared with the other theoretical models that are available in the literature, the presented model, in general, has a higher accuracy and precision.