Heat Transfer Performance Of Nanofluids Research Articles

Experimental research of convective heat transfer between nanofluids and high-temperature dense granite in deep geothermal reservoirs

Global warming is increasing as CO2 emissions from the use of conventional fossil fuels continue to rise. The development of geothermal energy is gradually becoming the key to the sustainable development of human society in the future. Enhancing the heat transfer performance of circulating heat transfer fluids is one of the effective means to efficiently exploit deep geothermal resources. In this study, a self-developed circulating heat exchange experimental setup was established. The convection heat transfer characteristics of nanofluids in high-temperature rocks were experimentally investigated. Al2O3 nanofluid and CuO nanofluid were used as the working medium for heat transfer in high temperature granite samples. The effects of the Reynolds number (1000–6000) and parameters such as nanoparticle type (CuO & Al2O3), size (20 nm & 40 nm) and mass fraction (0 wt%-2wt%) on the heat transfer intensity were analyzed. The effect of nanoparticle accumulation on the rock surface on the local heat transfer strength was also investigated. The results indicate that the increase of Reynolds number enhances the heat transfer strength of nanofluids in rocks. Nanofluid containing 20 nm Al2O3 nanoparticles has better heat transfer performance in rock than nanofluid containing 20 nm CuO nanoparticles. Meanwhile, the heat transfer performance of nanofluid containing 20 nm Al2O3 nanoparticles in rock is better than that of nanofluid containing 40 nm Al2O3 nanoparticles. The heat transfer intensity increases and then decreases as the nanoparticle mass fraction increases. The heat transfer coefficient at Reynolds number 6000 is 52.2 % higher than that of water. For nanofluids and water, the local heat transfer intensity decreases with increasing distance from the inlet. Meanwhile, accumulation of nanoparticles on rock surfaces during convective heat transfer enhances heat transfer intensity. The results show that nanofluids have the potential to be applied to deep geothermal resource extraction. This paper provides data and technical support for the application of nanomaterials in medium and deep geothermal systems to enhance heat transfer efficiency.

محاكاة تدفق السوائل النانوية الصفائحية على خطوة ساخنة مزدوجة مواجهة للخلف

This research focuses on heat transfer enhancement by separating flow over a double backward-facing step using nanofluid. To conduct this research, a numerical model was constructed using the ANSYS Workbench, and the governing equations were solved using the realizable k-ε model with a second-order upwind scheme. Three different types of base fluid (water, engine oil, and ethylene glycol) with nanoparticles (AL2O3, TiO2, and Cu) were used for Reynolds numbers ranging from 200 to 1000. The constant heat flux of the 2000 W/m2 boundary condition is considered on the lower wall. The effect of nanoparticle material, nanoparticle concentrations, nanoparticle sizes, and Reynolds numbers on the Nusselt number is investigated. Two different approaches for estimating nanofluid thermal conductivity and viscosity have been used. The numerical code results were verified with previous numerical data. The results showed that the peak of the Nusselt number occurs immediately after the steps. The results demonstrated a significant improvement in the heat transfer performance of nanofluids, especially Cu/engine oil nanofluids, compared to conventional base fluids with other nanoparticles. It was noticed that the Nusselt number increases with decreasing nanoparticle diameter and also with increasing Reynolds number.

Heat transfer evaluation of combined nanofluids in vertical annulus: An experimental and artificial neural network approach

Enhancing the thermal properties of the working fluid is a practical way to improve heat transfer performance. One of the suggested fluids for this purpose is nanofluids, which are suspensions of nanoparticles within a base fluid. Nanofluids have the potential to operate as a primary coolant or as an emergency coolant in a nuclear reactor. This paper investigates the thermal performance of a homogeneous hybrid nanofluid of Al2O3 and TiO2 in deionized water. The thermo-hydraulic performance of the nanofluid is analyzed in a high-pressure test loop capable of 25 bar pressure. The test section has an annular geometry, generating a cosine heat flux pattern. This flux pattern is representative of nuclear reactor cores. The experimental study is conducted to investigate the effects of nanoparticle concentration and Reynolds number on the heat transfer performance of nanofluids. The results show that increasing these two parameters significantly improved heat transfer. Specifically, raising the nanoparticle concentration from 0% to 1% leads to a reduction in surface temperature of 19% and 8% at Reynolds numbers of 825 and 4128, respectively. The calculated Nusselt numbers are compared with correlations from previous studies. Furthermore, an artificial neural network model is developed to predict heat transfer data for the studied system. The model consists of a single-layer feed-forward neural network trained with the stochastic gradient descent algorithm. To determine the optimal network, the number of neurons is optimized and evaluated based on the network's predictability. The neural network model demonstrates substantial improvements over previous experimental correlations (MAPE <2.5% and MSE <0.001).

Study of flow and heat transfer performance of nanofluids in curved microchannels with different curvatures

This study focuses on investigating the flow and heat transfer characteristics of Copper-water nanofluids (Cu-H2O) and water in microchannels with varying curvatures. The results reveal that Cu-H2O nanofluids demonstrate superior heat transfer performance compared to pure water in all four microchannels. Moreover, curved microchannels exhibit higher heat transfer performance than straight microchannels, regardless of whether the flow is laminar or turbulent. The heat transfer performance improves with increasing channel curvature, volume fraction of nanoparticles, and decreasing particle size. During laminar flow, the impact of curvature on heat transfer performance is more significant. However, during turbulent flow, variations in volume fraction have a greater influence on heat transfer performance compared to changes in curvature and particle size reduction. While larger volume fractions and higher curvatures increase flow resistance, this relationship is less pronounced for turbulent flow as Reynolds number and volume fraction increase. It is worth noting that the comprehensive heat transfer performance index does not consistently improve with increasing curvature, and sometimes straight microchannels outperform curved microchannels with specific curvatures. Additionally, curved microchannels exhibit a smaller average field synergy angle (FSA) compared to straight microchannels, indicating better synergy between the flow field and temperature field. The FSA also shows a relatively uniform distribution of local field synergy angles throughout the flow region in curved microchannels. Furthermore, the FSA decreases as the curvature increases.

Numerical Investigation of Nanofluid as a Coolant in a Prismatic Battery for Thermal Management Systems

Abstract This study delves into the realm of numerical investigation of the heat transfer performance of nanofluids as coolants for prismatic batteries. Nanofluids are being employed in battery cooling systems to enhance overall thermal management and ensure the safe operation of batteries, particularly in situations involving high heat generation. In this study, different types of nanofluids were used along with a base fluid of ethylene glycol–water (EG–water 50%). The energy equations consider the effects of viscous dissipation and heat generation. The model generates a set of nonlinear partial differential equations, which can be transformed into ordinary differential equations (ODEs) using appropriate similarity variables. These ODEs are then solved numerically by employing the Runge–Kutta–Fehlberg method along with the shooting method to obtain solutions. The simulations in both 2D and 3D showcase the results for various parameters pertaining to thermal and velocity fields, heat transfer rate, and drag force. The findings reveal that heat generation leads to a staggering increase in temperature of 78.22%. However, using aluminum nanoparticles (NPs) as opposed to copper nanoparticles quickly reduced the battery’s maximum temperature by 9.31%. The exceptional heat generation strengths of CuO–EG and Al2O3–EG nanofluids also resulted in a significant increase in their heat transfer rates of around 40.42% and 42.13%, respectively. Additionally, the aluminum NPs exhibited a more rapid heat transfer rate of 4.06% when compared to the copper nanoparticles. This research contributes to the development of improved cooling strategies for prismatic battery applications, ultimately paving the way for enhanced battery performance, an extended lifespan, and improved safety in a wide range of industries and electric vehicles.

Heat transfer enhancement of nanofluids in a four-blade LPD static mixer

The heat transfer performance of nanofluids within a four-bladed LPD static mixer was investigated using a combination of experiments and simulations under constant heat flow boundary conditions with Re ranging from 3519 to 16719. Al2O3-H2O nanofluid with volume fraction φ = 0.3 % was prepared experimentally and the stability of the nanofluid was analyzed by settling observation method and Dynamic light scattering (DLS). Numerical simulations were adopted to analyze the effects of nanoparticle types, volume fractions and types of mixing nanofluids on the heat transfer enhancement inside the four-bladed LPD static mixer. The results show that the maximum error of Nusselt number (Nu) between the predicted values of Mixture model and experimental values was 7.39 %. Because of the combined heat transfer performance coefficient PEC more than 1 with the increasing of Re, the mixers with α = 30° and β = 45° instead of KSM could be recommended when Re > 5279. The PEC of Al2O3-H2O nanofluids gradually increases with the increasing φ. At the same Re and φ, the flied synergy number Fc and PEC of the mixed nanofluids are 1.01–1.47 times and 1.15–3.35 times higher than those of the single nanofluids.

Effect of symmetrical and asymmetrical structures of transverse tube on heat transfer performance of nanofluids in a solar collector system

AbstractIn an effort to enhance the heat transfer performance of solar collectors, this paper proposed to replace the smooth tube with symmetrical and asymmetrical transversely corrugated tubes, and to couple with SiO2‐H2O nanofluids for heat transfer of solar collectors. Effects of nanofluids mass fraction (w = .0%, .1%, .3%, and .5%), Reynolds number (3000, 4000, 5000, 6000, and 7000), and groove radius (1.5, 2, and 2.5 mm) on the flow and heat transfer properties of nanofluids in solar collectors were studied. The comprehensive evaluation index was used to consider the heat transfer property and flow resistance of fluid flow at the same time. Results showed that with the augment of nanofluids mass fraction, Reynolds number, and groove radius, the heat transfer enhancement performance of the collector becomes better. Among them, when the Reynolds number is 4000, the asymmetric transversely corrugated tube with a nanofluids mass fraction of .5% and a groove depth of 2.5 mm has the best comprehensive flow and heat transfer performance, and the comprehensive evaluation index can reach 1.62. The study results in this paper are beneficial to the coupling of nanofluids and transversely corrugated tubes and their application in the domain of enhanced heat transfer of solar collectors.

Analysis of the Heat Transfer Performance of Nanofluids in Micro-Cylinder Groups

The objective of this study is to investigate, through numerical simulations, the flow and heat transfer characteristics of Al2O3, Cu, TiO2, and SiC water-based nanofluids flowing over micro-cylinder groups arranged in an inline configuration. The simulations were carried out under laminar flow conditions, and the analysis considered seven different low values of the Reynolds number, with a constant volume fraction of 2%. The aim of this investigation was to determine how nanofluids, i.e., suspensions of nanoparticles in water as the base fluid, can affect the pressure drop and heat transfer performance in micro-cylinder groups. To accomplish this, the finite volume method was employed to evaluate the impact of the nanofluids on pressure drop and heat transfer characteristics in the micro-cylinder groups. The study results demonstrate that, for all the nanofluids studied, the pressure drop and friction factor of the micro-cylinder groups increased with increasing Reynolds number. This behavior can be attributed to the interaction between the nanoparticles and the wall, which results in an increase in friction. Furthermore, the Nusselt number was found to increase with increasing Reynolds number. The SiC/Water nanofluid exhibited the highest Nusselt numbers among the four nanofluids tested, indicating that it provides better heat transfer performance than the other nanofluids. These results are consistent with experimental findings, indicating that the numerical simulations were accurate and reliable.

A numerical study on heat transfer performance using nanofluids in liquid cooling for cylindrical battery modules

The study investigates the heat transfer performance of nanofluids in liquid cooling for cylindrical battery modules. Two types of NFs, CuO/EG-water and Al2O3/EG-water, were used along with a base fluid of ethylene glycol–water (EG-water 50 %). The energy equations consider the effects of viscous dissipation and heat generation. The model produced a nonlinear system of partial differential equations (PDEs) that can be converted into ordinary differential equations (ODEs) by using appropriate similarity variables. The ODEs are then solved numerically using the shooting process in combination with the Runge-Kutta-Fehlberg method. The results for several parameters related to thermal, velocity fields, drag force, and HT rate are shown in the 2D and 3D simulations. The study provides insights into thermal and velocity profiles, fractional drag force, and heat transfer rate in a nanofluid flow around a cell in a cylindrical LIB module. According to the findings, the increase in volume fraction enhances the temperature of the two nanoparticles by (36.52 %, 44.20 %), respectively. CuO:EG-water nanofluids achieve ideal temperatures 7.68 % more quickly than Al2O3/EG-water nanofluids due to their distinct thermophysical properties. CuO/EG-water nanofluids show a 56.47 % temperature increase due to heat variation, whereas Al2O3/EG nanofluids experience a 16.30 % temperature decrease at Q < 0. Moreover, the drag force grows by 45.36 % and 47.94 %, while heat transfer increases by 50.17 % and 58.38 % due to nanoparticles. CuO:EG-water nanofluids exhibit better heat transfer performance, surpassing Al2O3:EG-water nanofluids by 8.20 %.

An innovative PDMS cell to improve the thermal conductivity measurements of nanofluids

The traditional methods to measure the thermal conductivity of nanofluids (NFs) do not allow the investigation of critical features that affect the NF's heat transfer performance. For instance, during the thermal conductivity measurements, the NF's thermal properties may be subject to several critical features such as sedimentation, aggregation and wall adhesion of NPs. In addition, the measurement cell has severe functional limitations in terms of full cleaning and performing direct visualizations due mainly to design, geometrical and material constraints. These are frequent problems encountered at the transient hot-wire and transient plane source (TPS) methods, two popular techniques often used to measure NF's thermal conductivity. In this way, polydimethylsiloxane (PDMS), due to its unique properties, such as thermal stability and excellent optical transparency, was applied to fabricate an innovative and simple cell that offers a more straightforward and efficient way to clean the NPs deposited on the walls and as a result to avoid any possible sample contaminations.

Experimental investigation of effect of iron oxide nanofluids with different morphology on heat transfer of multiple impinging jets

ABSTRACT This research aims to experimentally investigate the thermal performance of iron oxide nanofluids having different particle shapes for multiple impinging jet flow. The heat transfer performance of nanofluids with spherical like, faced nanocube and nanowires shapes prepared by hydrothermal synthesis was investigated experimentally. The weight percentage of the nanofluids examined in this study is 0.2 wt%, and different jet-to-jet spacing (B) and jet-to-plate distance (H) values were tested for each nanofluid. The experiments were carried out for laminar flow conditions, the temperature distribution was obtained through thermocouples, and the Nu number was calculated for each case. In experiments using nanowires, it was observed that the highest Nu numbers were obtained for jet-target/diameter ratio 2 for all cases (jet spaces and Reynolds numbers). Maximum Nu number enhancement was approximately 27.3% compared to pure water for the specified conditions. This value is quite significant since it was obtained with a relatively low concentration of nanofluids. It was observed that the particle size and morphology shape significantly impact nanofluids’ performance in heat transfer.

Bioconvective radiative unsteady Casson nanofluid flow across two concentric stretching cylinders with variable viscosity and variable thermal conductivity

The role of variable viscosity and variable thermal conductivity in nanofluid flows is significant, as they can strongly influence the flow behavior and heat transfer performance of nanofluids. Keeping in mind the importance of these effects of variable characteristics, our motivation in this study is to investigate the role of nonlinear radiative heat flux on unsteady Casson nanofluid flow across two concentric stretched cylinders in the presence of temperature-dependent viscosity and thermal conductivity. A convective condition on the inner cylinder wall is also considered. In addition, the nanofluid is immersed with microorganisms that can swim and move independently. The addition of microorganisms has a significant role in the stability of the nanofluid flow. The influence of thermophoresis and Brownian motion on the flow, heat, mass, and microorganisms are scrutinized by employing the Buongiorno model. The governing flow equations are converted into a system of differential equations engaging similarity transformations, and the bvp4c method is employed to solve it numerically. Engineering parameters are computed and tabulated numerically. The findings demonstrate that as the unsteadiness parameter upsurges, the radial profile intensifies while the axial profile diminishes near the outer cylinder surface. It is also comprehended that both Lewis and bioconvective Lewis numbers reduce the motile density profiles. The accuracy of the presented model is also given in a graphical illustration by comparing it with a published result in a limiting case.

Performance improvements of microchannel heat sink using Koch fractal structure and nanofluids

With the rapid development of microelectronics technology, the heat flux density in the micro-component system is very high. Therefore, the design of new and efficient cooling and heat dissipation devices has become an urgent problem to be solved. We use the Koch fractal structure and nanofluid to create a new type of microchannel heat sink. In this paper, a single-phase method is used to numerically study the flow and heat transfer properties of TiO2-water nanofluids in microchannels and optimize the structure with Koch fractal baffles. The effects of various volume fractions of nanofluids and baffles with varying structures on the inlet and exit pressure drop, flow resistance coefficient, substrate temperature, and Nusselt number (Nu) in the microchannel are investigated. In the Reynolds number (Re) range of 100–1000, the Nu of nanofluid increases with the increase of Re and the Nu increases from 18.19 to 60.41, which increases by 3.32 times, and the flow resistance of nanofluid falls by 1.79 times. Nanofluids' improved heat transfer factors are not all larger than one. The critical point is Re = 439, indicating that the combined heat transfer performance of nanofluids is superior to that of deionized water within the Re range of 100–439.

Heat transfer performance of nanofluids in heat exchanger: a review

Energy is a key aspect of any country’s economic development. Improving heat transfer performance leads to saving energy. Nanotechnology has a key role to play in optimizing heat exchangers. Fluids containing nanosized particles are called nanofluids. Nanofluids have higher thermal conductivity than typical liquids. This paper outlines current research on convective heat transfer performance, thermophysical properties, particle size, and volume concentration effects in nanofluid studies. M easurement m ethods f ort h ermal conductivity and correlations used by earlier researchers to determine thermal conductivity are also encompassed. The main applications of nanofluids as liibricants a nd radiator systems to improve the efficiency of he at removal fr om ve hicle en gines ha ve al so be en emphasized. Results suggest that by using a larger size of particle some drawbacks include particle sedimentation, clogging, erosion, stability, and increasing pressure drop. Enhancing thermal conductivity with optimum volume concentration. Improving the efficiency of heat exchange systems is one of the possible ways to reduce energy consumption. The need for optimum concentration of nanofluids is required. The Problem of stability, corrosion, and erosion arrived by increasing the volume concentration of nanoparticles in a nanofluid.

Reproduction of Nanofluid Synthesis, Thermal Properties and Experiments in Engineering: A Research Paradigm Shift

The suspension of different nanoparticles into various conventional thermal fluids to synthesize nanofluids has been proven to possess superior thermal, optical, tribological, and convective properties, and the heat transfer performance over conventional thermal fluids. This task appears trivial but is complicated and significant to nanofluid synthesis and its subsequent utilization in diverse applications. The stability of mono and hybrid nanofluids is significantly related to stirring duration and speed; volume, density, and base fluid type; weight/volume concentration, density, nano-size, and type of mono or hybrid nanoparticles used; type and weight of surfactant used; and sonication time, frequency, mode, and amplitude. The effects of these parameters on stability consequently affect the thermal, optical, tribological, and convective properties, and the heat transfer performance of nanofluids in various applications, leading to divergent, inaccurate, and suspicious results. Disparities in results have inundated the public domain in this regard. Thus, this study utilized published works in the public domain to highlight the trend in mono or hybrid nanofluid formulation presently documented as the norm, with the possibility of changing the status quo. With the huge progress made in this research area in which a large quantum of different nanoparticles, base fluids, and surfactants have been deployed and more are still emerging in the application of these advanced thermal fluids in diverse areas, there is a need for conformity and better accuracy of results. Reproduction of results of stability, thermal, optical, tribological, anti-wear, and fuel properties; photothermal conversion; and supercooling, lubrication, engine, combustion, emission, thermo-hydraulic, and heat transfer performances of formulated mono or hybrid nanofluids are possible through the optimization and detailed documentation of applicable nanofluid preparation parameters (stirring time and speed, sonication duration, amplitude, mode, frequency, and surfactant concentration) employed in formulating mono or hybrid nanofluids. This proposed approach is expected to project a new frontier in nanofluid research and serve as a veritable working guide to the nanofluid research community.

Influence of Preparation Characteristics on Stability, Properties, and Performance of Mono- and Hybrid Nanofluids: Current and Future Perspective

Nanofluids (NFs) synthesized via the suspension of diverse nanoparticles into conventional thermal fluids are known to exhibit better thermal, optical, tribological, and convective properties, photothermal conversion, and heat transfer performance in comparison with traditional thermal fluids. Stability is pivotal to NF preparation, properties, performance, and application. NF preparation is not as easy as it appears, but complex in that obtaining a stable NF comes with the harnessing of different preparation parameters. These parameters include stirring duration and speed, volume, density, base fluid type, weight/volume concentration, density, nano-size, type of mono or hybrid nanoparticles used, type and quantity of surfactant used, and sonication time, temperature, mode, frequency, and amplitude. The effect of these preparation parameters on the stability of mono and hybrid NFs consequently affects the thermal, optical, rheological, and convective properties, and photothermal conversion and heat transfer performances of NFs in various applications. A comprehensive overview of the influence of these preparation characteristics on the thermal, optical, rheological, and properties, photothermal conversion, and heat transfer performance is presented in this paper. This is imperative due to the extensive study on mono and hybrid NFs and their acceptance as advanced thermal fluids along with the critical importance of stability to their properties and performance. The various preparation, characterization, and stability methods deployed in NF studies have been compiled and discussed herein. In addition, the effect of the various preparation characteristics on the properties (thermal, optical, rheological, and convective), photothermal conversion, and heat transfer performances of mono and hybrid NFs have been reviewed. The need to achieve optimum stability of NFs by optimizing the preparation characteristics is observed to be critical to the obtained results for the properties, photothermal conversion, and heat transfer performance studies. As noticed that the preparation characteristics data are not detailed in most of the published works and thus making it mostly impossible to reproduce NF experimental studies, stability, and results; future research is expected to address this gap. In addition, the research community should be concerned about the aging and reusability of NFs (mono and hybrid) in the nearest future.

An experimental and numerical study of turbulent heat transfer enhancement for graphene nanofluids produced by pulsed discharge

• Time and cost-effective production of graphene nanofluids by pulsed discharge is tried and tested. • A new two-step method for producing graphene nanofluids has been developed. • Graphene nanofluids generated by pulsed discharge and ultrasound, like other graphene nanofluids, have high turbulent heat transfer performance (35% higher than water). • The numerical results show considerable increase in turbulent kinetic energy (8%) and velocity gradients near the wall due to physical interaction between continuous phase(water) and dispersed phase (graphene nano-particles). • The exchange of momentum and energy due to the movement of particles is considered as a cause-and-effect relationship between the aggregation of particles and the change in physical quantities in the continuous phase. Developing production methods for graphene nanofluids that can produce them in large quantities at once in a short time and at a low cost will contribute to the development of a wide range of industries that use nanofluids, and understanding their properties through mathematical modeling and experiments will lead to the development of new nanofluids. In this study, the new production method of graphene nanofluids is proposed and experimental and numerical investigations of the turbulent heat transfer performance of graphene nanofluids in a horizontal circular tube subjected to constant heat flux are conducted. The experimental investigation is conducted to evaluate the turbulent heat transfer performance of graphene nanofluids which are made by a new method using pulsed discharge and to compare them with numerical results. In the numerical investigation, the finite volume method with a Realizable k-ε model and Two-layer model is employed to solve the continuity, momentum, and energy conservation in two-dimensional domains. The Lagrangian two-phase model is applied to consider the physical interaction between the dispersed phase and continuous phase. In this model, the particles are tracked in a Lagrangian manner and coupled with the Eulerian flow description. Since the computational burden would be tremendous if individual nanoparticles were tracked in a Lagrangian manner, we defined a cluster of particles, called a parcel and treated it statistically. This concept of parcels allowed the average behavior of nanoparticles to be established as an analytical parameter. As a result, graphene nanofluids are not produced by pulsed discharge alone but are successfully produced by applying ultrasonic. Experimental investigations show a 33% increase in the Nu number of graphene nanofluid produced by pulsed discharge compared to water as the flow velocity increased. Numerical investigations confirm changes in the properties (Turbulent kinetic energy, Velocity distribution, Temperature distribution) of the continuous phase due to physical interactions between the dispersed and continuous phases. It is also shown that these changes contribute to the improved turbulent heat transfer performance of the nanofluid and that the aggregation of particles into the center of the tube is responsible for these changes.

Effect of Williamson parameter on Cu-water Williamson nanofluid over a vertical plate

The objective of this study is to analyze the augmentation of thermal conductivity and mass transfer rate over a semi-infinite vertical plate on account of nanoparticles suspended in Williamson fluid. Tiwari and Das model for nanofluids involving infinite shear rate viscosity is used in the current review to explain the heat transfer performance of nanofluids. The finite difference method of an implicit type is used to solve the governing dimensionless equations numerically. Graphical illustrations demonstrate the effects of the Williamson parameter on momentum, energy, and concentration, the behavior of skin friction coefficient and heat, and mass transfer rate. According to the present study, higher values of the Williamson parameter increases the skin friction, heat and mass transfer rate.The visualization of velocity, temperature, and concentration in the contour plots are also depicted. It is observed that Weissenberg number increases the velocity temperature and concentration of fluid flow near the plate significantly.

Mechanism analysis of the influence of nanoparticles on the convective heat transfer coefficient of traditional fluids

With the continuous progress of science and technology, the heat transfer performance of electronic chips and internal combustion engine pistons is increasingly required by industry. The traditional pure liquid can hardly meet the current heat transfer requirements, and it is known that the heat transfer performance of solids is always better than that of fluids. Therefore, adding solid particles to the fluid has a positive effect on the heat transfer performance of the fluid. In this paper, an experimental system is established to study the heat transfer performance of SiO2-water nanofluids, and the variation of each physical parameter and convective heat transfer coefficient of SiO2-water nanofluids flowing in a circular tube at different volume fractions is measured. The microscopic mechanism of the enhanced heat transfer of nanofluids is also analyzed from the perspective of nanoparticle's micro-motion by numerical simulation. The results show that the convective heat transfer coefficients of nanofluids gradually increase with increasing volume fraction of nanoparticles under the same conditions. The convective heat transfer coefficients of SiO2-water nanofluids with volume fractions of 0.5 %, 1 %, and 2 % increase by 15.1 %, 25.9 %, and 36.8 %, respectively, compared with pure water. Then the extent of the effect of nanofluid physical parameter changes and nanoparticle micro-motion on the improvement of nanofluid heat transfer performance is analyzed. It is found that the micro-motion of nanoparticles has a greater effect on the enhanced heat transfer of nanofluids compared to the variation of physical parameters. It is also found that the conventional convective heat transfer coefficient formulation for single-phase flow is not applicable to calculate the convective heat transfer coefficient of SiO2-water nanofluids. Therefore, the new formulations based on the convective heat transfer coefficient of SiO2-water nanofluids in different flow regimes are established.

다양한 매개변수에 따른 관내 나노유체의 성능지수

The figure of merit for nanofluids represents the heat transfer performance of nanofluids against basic fluid. In previous studies, only the material properties of nanofluids have been considered for the figure of merit. In this study, the computational thermal flow analyses are performed including not only the material properties but also the geometric shapes and the external effects. The figures of merit are obtained with the four parameters, which are the inlet pressure, the number of return bends, the radius of curvature, and the volume fraction of nanoparticles in the pipes with the return bends. The results show that the three remaining parameters other than the number of return bends act on the figures of merit in a complicated manner. Therefore, a correlation equation with Euler number, Dean number, and Prandtl number associated with the three parameters is derived through the nonlinear regression. These results are expected to be helpful in designing and manufacturing heat exchangers using nanofluids.