The impact of various nanofluid types on triangular microchannels heat sink cooling performance

This paper discusses the impact of using various types of nanofluids on heat transfer and fluid flow characteristics in triangular shaped microchannel heat sink (MCHS). In this study, an aluminum MCHS performance is examined using water as a base fluid with different types of nanofluids such as Al₂O₃, Ag, CuO, diamond, SiO₂, and TiO₂ as the coolants with nanoparticle volume fraction of 2%. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using the finite volume method. It is inferred that diamond-H₂O nanofluid has the lowest temperature and the highest heat transfer coefficient, while Al₂O₃-H₂O nanofluid has the highest temperature and the lowest heat transfer coefficient. SiO₂-H₂O nanofluid has the highest pressure drop and wall shear stress while Ag-H₂O nanofluid has the lowest pressure drop and wall shear stress among other nanofluid types. Based on the presented results, diamond-H₂O and Ag-H₂O nanofluids are recommended to achieve overall heat transfer enhancement and low pressure drop, respectively, compared with pure water.     

Heat transfer in rectangular microchannels heat sink using nanofluids

The effect of using nanofluids on heat transfer and fluid flow characteristics in rectangular shaped microchannel heat sink (MCHS) is numerically investigated for Reynolds number range of 100–1000. In this study, the MCHS performance using alumina–water (Al₂O₃-H₂O) nanofluid with volume fraction ranged from 1% to 5% was used as a coolant is examined. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using finite volume method. The MCHS performance is evaluated in terms of temperature profile, heat transfer coefficient, pressure drop, friction factor, wall shear stress and thermal resistance. The results reveal that when the volume fraction of nanoparticles is increased under the extreme heat flux, both the heat transfer coefficient and wall shear stress are increased while the thermal resistance of the MCHS is decreased. However, nanofluid with volume fraction of 5% could not be able to enhance the heat transfer or performing almost the same result as pure water. Therefore, the presence of nanoparticles could enhance the cooling of MCHS under the extreme heat flux conditions with the optimum value of nanoparticles. Only a slight increase in the pressure drop across the MCHS is found compared with the pure water-cooled MCHS.     

Heat transfer enhancement in microchannel heat sinks using nanofluids

Heat transfer enhancement in a 3-D microchannel heat sink (MCHS) using nanofluids is investigated by a numerical study. The addition of nanoparticles to the coolant fluid changes its thermophysical properties in ways that are closely related to the type of nanoparticle, base fluid, particle volume fraction, particle size, and pumping power. The calculations in this work suggest that the best heat transfer enhancement can be obtained by using a system with an Al₂O₃–water nanofluid-cooled MCHS. Moreover, using base fluids with lower dynamic viscosity (such as water) and substrate materials with high thermal conductivity enhance the thermal performance of the MCHS. The results also show that as the particle volume fraction of the nanofluid increases, the thermal resistance first decreases and then increases. The lowest thermal resistance can be obtained by properly adjusting the volume fraction and pumping power under given geometric conditions. For a moderate range of particle sizes, the MCHS yields better performance when nanofluids with smaller nanoparticles are used. Furthermore, the overall thermal resistance of the MCHS is reduced significantly by increasing the pumping power. The heat transfer performance of Al₂O₃–water and diamond–water nanofluids was 21.6% better than that of pure water. The results reported here may facilitate improvements in the thermal performance of MCHSs.     

Experimental microchannel heat sink performance studies using nanofluids

In this study, microchannel heat sink (MCHS) performance using nanofluids as coolants is addressed. We first carried out a simple theoretical analysis that indicated more energy and lower MCHS wall temperature could be obtained under the assumption that heat transfer could be enhanced by the presence of nanoparticles. Experiments were then performed to verify the theoretical predictions. A silicon MCHS was made and CuO–H₂O mixtures without a dispersion agent were used as the coolants. The CuO particle volume fraction was in the range of 0.2 to 0.4%. It was found that nanofluid-cooled MCHS could absorb more energy than water-cooled MCHS when the flow rate was low. For high flow rates, the heat transfer was dominated by the volume flow rate and nanoparticles did not contribute to the extra heat absorption. The measured MCHS wall temperature variations agreed with the theoretical prediction for low flow rate. For high flow rate, the measured MCHS wall temperatures did not completely agree with the theoretical prediction due to the particle agglomeration and deposition. It was also found that raising the nanofluid bulk temperature could prevent the particles from being agglomerated into larger scale particle clusters. The experimental result also indicated that only slightly increase in pressure drop due to the presence of nanoparticles in MCHS operation.     

Influence of channel shape on the thermal and hydraulic performance of microchannel heat sink

Microchannel heat sinks (MCHS) can be made with channels of various shapes. Their size and shape may have remarkable influence on the thermal and hydrodynamic performance of MCHS. In this paper, numerical simulations are carried out to solve the three-dimensional steady and conjugate heat transfer governing equations using the Finite-Volume Method (FVM) of a water flow MCHS to evaluate the effect of shape of channels on the performance of MCHS with the same cross-section. The effect of shape of the channels on MCHS performance is studied for different channel shapes such as zigzag, curvy, and step microchannels, and it is compared with straight and wavy channels. The MCHS performance is evaluated in terms of temperature profile, heat transfer coefficient, pressure drop, friction factor, and wall shear stress. Results show that for the same cross-section of a MCHS, the temperature and the heat transfer coefficient of the zigzag MCHS is the least and greatest, respectively, among various channel shapes. The pressure drop penalty for all channel shapes is higher than the conventional straight MCHS. The zigzag MCHS has the highest value of pressure drop, friction factor, and wall shear stress followed by the curvy and step MCHS, respectively.     

Influence of nanofluids on parallel flow square microchannel heat exchanger performance

The effects of using various types of nanofluids and Reynolds numbers on heat transfer and fluid flow characteristics in a square shaped microchannel heat exchanger (MCHE) is numerically investigated in this study. The performance of an aluminum MCHE with four different types of nanofluids (aluminum oxide (Al₂O₃), silicon dioxide (SiO₂), silver (Ag), and titanium dioxide (TiO₂)), with three different nanoparticle volume fractions of 2%, 5% and 10% using water as base fluid is comprehensively analyzed. The three-dimensional steady, laminar developing flow and conjugate heat transfer governing equations of a balanced MCHE are solved using the finite volume method. The MCHE performance is evaluated in terms of temperature profile, heat transfer rate, heat transfer coefficient, pressure drop, wall shear stress pumping power, effectiveness, and overall performance index. The results reveal that nanofluids can enhance the thermal properties and performance of the heat exchanger while having a slight increase in pressure drop. It was also found that increasing the Reynolds number causes the pumping power to increase and the effectiveness to decrease.     

Numerical simulation of heat transfer enhancement in wavy microchannel heat sink

In this paper, heat transfer and water flow characteristics in wavy microchannel heat sink (WMCHS) with rectangular cross-section with various wavy amplitudes ranged from 125 to 500 μm is numerically investigated. This investigation covers Reynolds number in the range of 100 to 1000. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using the finite-volume method (FVM). The water flow field and heat transfer phenomena inside the heated wavy microchannels is simulated and the results are compared with the straight microchannels. The effect of using a wavy flow channel on the MCHS thermal performance, the pressure drop, the friction factor, and wall shear stress is reported in this article. It is found that the heat transfer performance of the wavy microchannels is much better than the straight microchannels with the same cross-section. The pressure drop penalty of the wavy microchannels is much smaller than the heat transfer enhancement achievement. Both friction factor and wall shear stress are increased proportionally as the amplitude of wavy microchannels increased.     

Pressure drop and thermal characteristics of CuO-base oil nanofluid laminar flow in flattened tubes under constant heat flux

An experimental investigation has been carried out to study the heat transfer and pressure drop characteristics of nanofluid flow inside horizontal flattened tubes under constant heat flux. The nanofluid is prepared by dispersion of CuO nanoparticle in base oil and stabilized by means of an ultrasonic device. Nanofluids with different particle weight concentrations of 0.2%, 0.5%, 1% and 2% are used. Copper tubes of 11.5 mm I.D. are flattened into oblong shapes and used as test sections. The nanofluid flowing inside the tube is heated by an electrical heating coil wrapped around it. Required data are acquired for laminar and hydrodynamically fully developed flow inside round and flattened tubes.The effect of different parameters such as flow Reynolds number, flattened tube internal height and nanofluid particle concentration on heat transfer coefficient and pressure drop of the flow is studied. Observations show that the heat transfer performance is improved as the tube profile is flattened. Flattening the tube profile resulted in pressure drop increasing. In addition, the heat transfer coefficient as well as pressure drop is increased by using nanofluid instead of base fluid. Furthermore, the performance evaluation of the two enhanced heat transfer techniques studied in this investigation shows that applying flattened tubes instead of the round tube is a more effective way to enhance the convective heat transfer coefficient compared to the second method which is using nanofluids instead of the base liquid.     

An empirical study on heat transfer and pressure drop properties of heat transfer oil-copper oxide nanofluid in microfin tubes

In this paper, the convective heat transfer of the heat transfer oil-copper oxide nanofluid flow in horizontal smooth and microfin tubes is investigated experimentally. Using a flow control system, the flow regime is always laminar and the wall temperature is constant by using a steam tank. Pure heat transfer oil and nanofluid with the weight concentrations of 0.5%, 1% and 1.5% are used as working fluids. The results are in good agreement with the classic correlations for the pure fluid flow. Based on the results, combination use of nanoparticles and the microfin tube leads to the heat transfer enhancement up to 230%, in comparison with the base fluid flow in the smooth tube. The results are useful in the prediction of the heat transfer rate and the pressure drop in nanofluid flows.     

An experimental study of a confined and submerged impinging jet heat transfer using Al2O3-water nanofluid

An experimental investigation was performed to study the heat transfer performance of a 36 nm-Al₂O₃-particle–water nanofluid in a confined and submerged impinging jet on a flat, horizontal and circular heated surface. The tests were realized for the following ranges of the governing parameters: the nozzle diameter is 3 mm and the distance nozzle-to-heated-surface was set to 2, 5 and 10 mm; the flow Reynolds number varies from 3800 to 88 000, the Prandtl number from 5 to 10, and the particle volume fraction is ranging from 0 to 6%. Experimental data, obtained for both laminar and turbulent flow regimes, have clearly shown that, depending upon the combination of nozzle-to-heated surface distance and particle volume fraction, the use of a nanofluid can provide a heat transfer enhancement in some cases; conversely, for other combinations, an adverse effect on the convective heat transfer coefficient may occur. Within the experimental parameters used, it has been observed that highest surface heat transfer coefficients can be achieved using an intermediate nozzle-to-surface distance of 5 mm and a 2.8% particle volume fraction nanofluid. Nanofluids with high particle volume fractions, say 6% or higher, have been found not appropriate for the heat transfer enhancement purpose under the confined impinging jet configuration. On the other hand, for a very small and a large distance of nozzle-to-heated-surface, it has been observed that the nanofluid use does not provide a perceptible heat transfer enhancement and has, for some particular cases, produced a clear decrease of the convective heat transfer coefficient while compared to that obtained using distilled water.     

Investigation of thermohydraulic performance of triple concentric-tube heat exchanger with CuO/water nanofluid: Numerical approach

In this study, numerical investigation of CuO/water nanofluids in a triple concentric-tube heat exchanger has been carried out using a commercial CFD software. The primary objective of this study is to conduct a heat transfer and pressure drop characteristics of water-based CuO nanofluids under turbulent flow regime. Reynolds number for the nanofluid has also been considered in the range of 2500 to 10,000 with a nanoparticle volume concentration of 0% to 3%. The effects of flow rate, volume concentration of nanoparticles, and flow arrangement on heat transfer performance of nanofluid have been studied for four flow arrangements. The comparison of the performance with and without nanofluid has been done. It was found that thermal performance and overall effectiveness increased with the increase in Reynolds number and volume concentration of nanoparticles in all the four flow arrangements for the considered range of operating parameters.     

Numerical investigation of porous rib arrangement on heat transfer and entropy generation of nanofluid flow in an annulus using a two-phase mixture model

The effect of porous rib arrays on the heat transfer and entropy generation of laminar nanofluid flow inside annuli is studied numerically, using a two-phase mixture model for nanofluid flow simulation. Porous media, nanoparticles, and vortex formation are simultaneously affecting the characteristics of the system. Results showed that the permeability and height of porous ribs have significant effects on the thermal performance of system. Vortex zones also affect the trend of variation of entropy and performance numbers, and local optimums exist for these two parameters. The role of nanofluid in heat transfer enhancement in recirculating zones is more significant for higher volume fractions.     

Analytical analysis of heat transfer and pumping power of laminar nanofluid developing flow in microchannels

Thermal management issues are limiting barriers to high density electronics packaging and miniaturization. Liquid cooling using micro and mini channels is an attractive alternative to large and bulky aluminum or copper heat sinks. These channels can be integrated directly into a chip or a heat spreader, and cooling can be further enhanced using nanofluids (liquid solutions with dispersed nanometer-sized particles) due to their enhanced heat transfer effects reported in literature. The goals of this study are to evaluate heat transfer improvement of a nanofluid heat sink with developing laminar flow forced convection, taking into account the pumping power penalty. The phrase heat transfer enhancement ratio (HTR) is used to denote the ratio of average heat transfer coefficient of nanofluid to water at the same pumping power. The proposed model uses semi-empirical correlations to calculate nanofluid thermophysical properties. The predictions of the model are found to be in good agreement with experimental studies. The validated model is used to identify important design variables (Reynolds number, volume fraction and particle size) related to thermal and flow characteristics of the microchannel heat sink with nanofluids. Statistical analysis of the model showed that the volume fraction is the most significant factor impacting the HTR, followed by the particle diameter. The impact of the Reynolds number and other interaction terms is relatively weak. The HTR is maximized at smallest possible particle diameter (since smaller particles improve heat transfer but do not impact pumping power). Then, for a given Reynolds number, an optimal value of volume fraction can be obtained to maximize HTR. The overall aim is to present results that would be useful for understanding and optimal design of microchannel heat sinks with nanofluid flow.     

Experimental study of Fe2O3/water and Fe2O3/ethylene glycol nanofluid heat transfer enhancement in a shell and tube heat exchanger

Heat transfer characteristics of Fe₂O₃/water and Fe₂O₃/EG nanofluids were measured in a shell and tube heat exchanger under laminar to turbulent flow condition. In the shell and tube heat exchanger, water and ethylene glycol-based Fe₂O₃ nanofluids with 0.02%, 0.04%, 0.06% and 0.08% volume fractions were used as working fluids for different flow rates of nanofluids. The effects of Reynold's number, volume concentration of suspended nanoparticles and different base fluids on the heat transfer characteristics were investigated. Based on the results, adding nanoparticles to the base fluid causes a significant enhancement of the heat transfer characteristics and thermal conductivity. This enhancement was investigated with regard to various factors; concentration of nanoparticles, types of base fluids, sonication time and temperature of fluids. In this paper, the effect of Fe₂O₃ nanoparticles on the thermal conductivity of base fluids like ethylene glycol and water was studied. The thermal conductivity measurement was made for different concentrations and temperatures. As the concentration of the nanoparticles increased, there was a significant enhancement in thermal conductivity and overall heat transfer due to more interaction between particles. It was also observed that there was an improvement in the thermal conductivity of the base fluid as the temperature increased. The measurements also showed that the pressure drop of nanofluid was higher than that of the base fluid in a turbulent flow regime. However, there was no significant increase in pressure drop at laminar flow.     

Effect of nanoparticles size on thermal performance of nanofluid in a trapezoidal microchannel-heat-sink

This paper deals with spherical nanoparticles size effects on thermal performance and pressure drop of a nanofluid in a trapezoidal microchannel-heat-sink (MCHS). Eulerian–Eulerian two-phase numerical approach is utilized for forced convection laminar, incompressible and steady three dimensional flow of copper-oxide nanoparticles with water as base fluid at 100 to 200 nm diameter and 1% to 4% volume concentration range. Continuity, momentum, energy and volume conservation equations are solved at whole of the computational domain via finite volume method. Obtained results signify that pressure drop increases 15% at Re = 500 and 1% volume concentration while nanoparticles diameter increases from 100 to 200 nm. By increasing volume concentration, nanoparticles size effect becomes more prominent and it is observed that increment rate of pressure drop is intensified for above 150 nm particles diameter. Unlike the pressure drop, heat transfer decreases with an increase in nanoparticles diameter. Also, it is observed that with an increase in nanoparticles diameter, average Nusselt number of base fluid decreases more than that of the nanoparticles and this signifies that base fluid has more efficacy on thermal performance of copper-oxide nanofluid.     

A lattice Boltzmann simulation of enhanced heat transfer of nanofluids

Due to its distinctive characteristics nanofluid has drawn much attention from academic communities since the last decade. Compared with conventional fluids, nanofluid has higher thermal conductivity and surface to volume ratio, which enables it to be an effective working fluid in terms of heat transfer enhancement. Recent experimental works have shown that with low nanoparticle concentrations (1–5 vol.%), the effective thermal conductivity of the suspensions can increase by more than 20% for various mixtures. Although many outstanding experimental works have been carried out, the fundamental understanding of nanofluid characteristics and performance is still not sufficient. Much more theoretical and numerical studies are required. Over the past two decades, the lattice Boltzmann method (LBM) has experienced a rapid development and well accepted as a useful method to simulate various fluid behaviours. In the present study, the LBM is employed to investigate the characteristics of nanofluid flow and heat transfer. By coupling the density and temperature distribution functions, the hydrodynamics and thermal features of nanofluids are properly simulated. The effects of the parameters including Rayleigh number and volume fraction of nanoparticles on hydrodynamic and thermal performances are investigated. The results show that both Rayleigh number and solid volume fraction of nanoparticles have influences on heat transfer enhancement of nanofluids; and there is a critical value of Rayleigh number on the performance of heat transfer enhancement.     

Thermal performance augmentation using water based Al2O3-gamma nanofluid in a horizontal shell and tube heat exchanger under forced circulation

Shell and tube heat exchanger is one of the most prevalent heat exchangers with a wide variety of industrial applications, i.e., power plants, chemical processes, marine industries, HVAC systems, cooling of hydraulic fluid and engine oil in heavy duty diesel engines and the like specifically where a need to heat or cool a large fluid volume exist and also higher-pressure use. In the present study, the effect of using Al₂O₃-water nanofluid on thermal performance of a commercial shell and tube heat exchanger with segmental baffles is assessed experimentally. For this purpose, Al₂O₃-gamma nanoparticles with 15 nm mean diameter (99.5% purity) and Sodium Dodecyl Benzene Sulphonate (SDBS) as surfactant are used to make aqueous Al₂O₃ nanofluid at three various volume fractions of nanoparticles (φ = 0.03, 0.14 and 0.3%). Indeed, in this paper the effect of some parameters of hot working fluid such as Reynolds number and volume concentration of nanoparticles on heat transfer characteristics, friction factor and thermal performance factor of a shell and tube heat exchanger under laminar flow regime is investigated. The results indicate a substantial increment in Nusselt number as well as the overall heat transfer coefficient of heat exchanger by enhancement of Reynolds number and it can be seen that, at a certain Reynolds number, heat transfer characteristics of heat exchanger increase as the nanoparticles volume concentration increases. Outcomes of the heat transfer evaluation demonstrate that applying nanofluids instead of base fluid lead to increment of Nusselt number up to 9.7, 20.9 and 29.8% at 0.03, 0.14 and 0.3 vol%, respectively. Likewise it is seen that at mentioned nanoparticles volume fractions, overall heat transfer coefficient of heat exchanger enhances around 5.4, 10.3 and 19.1%, respectively. In term of pressure drop, a little penalty is found by using nanofluid in the test section. Eventually a thermal performance assessment on the heat exchanger was conducted. According to the analysis results, utilizing nanofluid at minimum and maximum nanoparticles volume fractions (φ = 0.03 and 0.3%) results in average augmentation of around 6.5% and 18.9% in thermal performance factor (η) of the heat exchanger compared to the base liquid, respectively.     

Numerical study of microchannel heat sink performance using nanofluids

This study presents the numerical simulation of three-dimensional incompressible steady and laminar and turbulent fluid flow of a trapezoidal micro-channel heat sink (MCHS) using CuO/water nanofluid as a cooling fluid. Navier–Stokes equations with conjugate energy equation are discretized by the finite-volume method. CFD predictions of laminar and turbulent forced convection of CuO/water nanofluids by single-phase and two-phase models (mixture model) are compared. The parameters studied include the particle volume fraction (ϕ = 0.204 %, 0.256%, 0.294% and 0.4%), and the volumetric flow rate ($\dot{\mathit{V}}=10\mathrm{mL}/min$, 15 mL/min and 20 mL/min). Comparisons of the thermal resistance predicted by the single-phase and two-phase models with corresponding experimental results show that the two-phase model is more accurate than the single-phase model. In the laminar flow, the thermal resistance of nanofluids is smaller than that of the water, which decreases as the particle volume fraction and the volumetric flow rate increase. In addition, the pressure drop of both nanofluid-cooled MCHS and pure water-cooled MCHS is discussed. For the laminar flow case, the pressure drop increases slightly for nanofluid-cooled MCHS.     

An experimental study of forced convective heat transfer for fully developed Al 2 O 3 –water nanofluid in an annulus tube

Nanofluids have been known as practical materials to ameliorate heat transfer within diverse industrial systems. The current work presents an empirical study on forced convection effects of Al₂O₃–water nanofluid within an annulus tube. A laminar flow regime has been considered to perform the experiment in high Reynolds number range using several concentrations of nanofluid. Also, the boundary conditions include a constant uniform heat flux applied on the outer shell and an adiabatic condition to the inner tube. Nanofluid particle is visualized with transmission electron microscopy to figure out the nanofluid particles. Additionally, the pressure drop is obtained by measuring the inlet and outlet pressure with respect to the ambient condition. The experimental results showed that adding nanoparticles to the base fluid will increase the heat transfer coefficient (HTC) and average Nusselt number. In addition, by increasing viscosity effects at maximum Reynolds number of 1140 and increasing nanofluid concentration from 1% to 4% (maximum performance at 4%), HTC increases by 18%.     

Effect of laminar separation flow and nanofluids on heat transfer augmentation with passive techniques: A review

Heat transfer in flow channels can be improved by using passive techniques such as ribs on wall and change cross section area where these modifications have practical engineering application for thermal power plant, refrigerators, and radiators. Effects of separation flow and nanofluids on thermal performance for laminar range presented experimentally and numerically in this review. The augmentations of heat transfer with fluid and nanofluid flow through sudden expansion, over backward and forward facing step, and rib channels have been concerned. The experimental results showed good agreement with numerical results and indicated the effects of separation flow and nanoparticles on augmentation of heat transfer rate. The results showed increase in Nusselt number with increase of Reynolds number, step height, and number of ribs. It was detected that by increasing the nanoparticle volume concentrations of nanofluids, improves the heat transfer coefficient. Also different nanoparticles used in the literature investigations are based on thermal conductivity where enhancement of heat transfer rate was obtained significantly.