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.     

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 enhancement with the use of nanofluids in radial flow cooling systems considering temperature-dependent properties

Heat transfer enhancement capabilities of coolants with suspended metallic nanoparticles inside typical radial flow cooling systems are numerically investigated in this paper. The laminar forced convection flow of these nanofluids between two coaxial and parallel disks with central axial injection has been considered using temperature dependent nanofluid properties. Results clearly indicate that considerable heat transfer benefits are possible with the use of these fluid/solid particle mixtures. For example, a Water/Al₂O₃ nanofluid with a volume fraction of nanoparticles as low as 4% can produce a 25% increase in the average wall heat transfer coefficient when compared to the base fluid alone (i.e., water). Furthermore, results show that considerable differences are found when using constant property nanofluids (temperature independent) versus nanofluids with temperature dependent properties. The use of temperature-dependent properties make for greater heat transfer predictions with corresponding decreases in wall shear stresses when compared to predictions using constant properties. With an increase in wall heat flux, it was found that the average heat transfer coefficient increases whilst the wall shear stress decreases for cases using temperature-dependent nanofluid properties.     

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.     

Heat transfer performance and exergy analyses of a corrugated plate heat exchanger using metal oxide nanofluids

Heat exchangers have been widely used for efficient heat transfer from one medium to another. Nanofluids are potential coolants, which can afford excellent thermal performance in heat exchangers. This study examined the effects of water and CuO/water nanofluids (as coolants) on heat transfer coefficient, heat transfer rate, frictional loss, pressure drop, pumping power and exergy destruction in the corrugated plate heat exchanger. The heat transfer coefficient of CuO/water nanofluids increased about 18.50 to 27.20% with the enhancement of nanoparticles volume concentration from 0.50 to 1.50% compared to water. Moreover, improvement in heat transfer rate was observed for nanofluids. On the other hand, exergy loss was reduced by 24% employing nanofluids as a heat transfer medium with comparing to conventional fluid. Besides, 34% higher exergetic heat transfer effectiveness was found for 1.5 vol.% of nanoparticles. It has a small penalty in the pumping power. Hence, the plate heat exchanger performance can be improved by adapting the working fluid with CuO/water nanofluids.     

Heat transfer and fluid flow of nanofluids in laminar radial flow cooling systems

Nanofluids are considered as interesting alternatives to conventional coolants. It is well known that traditional fluids have limited heat transfer capabilities when compared to common metals. It is therefore quite conceivable that a small amount of extremely fine metallic particles placed in suspension in traditional fluids will considerably increase their heat transfer performances. A numerical investigation into the heat transfer enhancement capabilities of coolants with suspended metallic nanoparticles inside a radial, laminar flow cooling configuration is presented. Temperature dependant nanofluid properties are evaluated from experimental data available in recent literature. Results indicate that considerable heat transfer increases are possible with the use of relatively small volume fractions of nanoparticles. Generally, however, these are accompanied by considerable increases in wall shear-stress. Results also show that predictions obtained with temperature variable nanofluid properties yield greater heat transfer capabilities and lower wall shear stresses when compared to predictions using constant properties.     

Lattice Boltzmann simulation of mixed convection heat transfer in a corrugated wall cavity utilizing water‐based nanofluids

In the present study, the effects of Cu and CuO nanoparticles' presence on mixed convection heat transfer in a lid‐driven cavity with a corrugated wall are investigated using the lattice Boltzmann method. The boundary fitting method with second‐order accuracy at both velocity and temperature fields is used to simulate the curved boundaries in the LBM. The problem is investigated for different Richardson numbers (0.1–10), volume fractions of nanoparticles (0–0.05), curve amplitudes (0.05–0.25), and phase shifts of corrugated wall (0–270) when the Reynolds number is equal to 25. The volume fraction of added nanoparticles to the water‐based fluid is less than 0.05 to make dilute suspensions. Results show that adding nanoparticles enhances the rate of heat transfer. It is found that nanoparticles have significant effects on both fluid flow and heat transfer of the mixed convection, especially for low Richardson numbers. A comparison between Cu and CuO nanoparticles shows the Cu nanoparticles have a better effect on heat transfer enhancement for all tested conditions. The results also represent the effective role of a corrugated wall on the rate of nanofluid heat transfer. It is observed that increasing the wavy wall's amplitude leads to a decrease of the average Nusselt numberfor a high Richardson number. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21024     

Experimental and analytical investigation on an automobile radiator with CuO/EG‐water based nanofluid as coolant

In the present study, experimental and analytical thermal performance of automobile radiator using nanofluids is investigated and compared with performance obtained with conventional coolants. Effect of operating parameters and nanoparticle concentration on heat transfer rate are studied for water as well as CuO/EG‐water based nanofluid analytically. The results are presented in the form of graphs showing variations of net heat transfer rate for various coolant flow rate, air velocity, and source temperature for various CuO/EG‐water based nanofluids. Experimental results indicate that with the increase in coolant flow rate and air velocity, heat transfer rate increases, reaches maximum and then decreases. Experimental investigation of a radiator is carried out using CuO/EG‐water based nanofluids. Results obtained by experimental work and analytical MATLAB code are almost the same. Maximum absolute error in water and air side is within 12% for all flow condition and coolant fluids. Nusselt number of nanofluid is calculated using equation number 33[9]. The results obtained from experimental work using 0.2% volume CuO/EG‐water based nanofluids are compared with the results obtained from MATLAB code. The results show that the maximum error in the outlet temperature of the coolant and air is 12% in each case. Thus MATLAB code can be used for different concentration of nanofluids to study the effect of operating parameters on heat transfer rate. Thus MATLAB code developed is valid for given heat exchanger applications. From the results obtained by already validated MATLAB code, it is concluded that increase in coolant flow rate, air velocity, and source temperature increases the heat transfer rate. Addition of nanoparticles in the base fluid increases the heat transfer rate for all kind of base fluids. Among all the nanofluid analyzed in this study, water‐based nanofluid gives highest value of heat transfer rate and is recommended for the heat exchanger applications under normal operating conditions. Maximum enhancement is observed for ethylene glycol‐water (4:6) mixture for 1% volume concentration of CuO is almost equal to 20%. As heat transfer rate increases with the use of nanofluids, the heat transfer area of the radiator can be minimized.     

Magnetohydrodynamic MgO/CuO‐water hybrid nanofluid flow driven by two distinct geometries

Research regarding the heat transit mechanism of magnetohydrodynamic hybrid nanoliquid flow over contrasting flow profiles is predominantly employed in transpiration, coolants, fiber coatings, heat exchangers, and so on. Owing to this, we intend to dissect the heat transport behavior of MHD hybrid nanofluid flow past a cone as well as a wedge. For the analysis, we take nonlinear radiation and viscous dissipation into consideration with 30% of ethylene glycol and water (or EGW) as base fluid with suspended copper oxide (CuO) and magnesium oxide (MgO) nanoparticles. The Runge‐Kutta method with the shooting technique is utilized to figure out the deduced nonlinear gotverning equations. The influence of the concerned different admissible parameters on similar distributions (cone and wedge) are graphically illustrated and interpreted accordingly via computed numerical values. It is worth noting that the heat transport rate is greater past the cone rather than the wedge. The presence of CuO and MgO hybrid nanoparticles increases the heat transfer rate of the EGW base fluid.     

Experimental investigation of convective heat transfer coefficient of Al2O3/water nanofluid at lower concentrations in a car radiator

For many years, water and ethylene glycol were used as conventional coolants in automotive car radiators, but these coolants offer lower thermal conductivity than is required. This study is focused on the application of water‐based Al₂O₃ nanofluid at lower concentrations in a car radiator. The Al₂O₃ nanoparticles with an average diameter of 50 nm are dispersed in demineralized water at four different volume concentrations (0.1 vol. % to 0.4 vol. %) without any dispersant or stabilizer. Flow rate is varied in the range of 2 l/min to 5 l/min and inlet coolant temperature to the radiator is set to 50 °C, 60 °C, and 70 °C. The results show that the heat transfer coefficient increases with an increase in particle concentration, flow rate, and inlet temperature of coolant and the maximum increase in heat transfer coefficient is 45.87 % compared to pure water. However, the Nusselt number increases with the increase in particle concentration, Reynolds number, and inlet temperature of the coolant. In addition with the experimental study, a regression analysis is performed by using the ANOVA method and generates a correlation for the convective heat transfer coefficient.     

Influence of various base nanofluids and substrate materials on heat transfer in trapezoidal microchannel heat sinks

Numerical investigations are performed to investigate the laminar flow and heat transfer characteristics of trapezoidal MCHS using various types of base nanofluids and various MCHS substrate materials on MCHS performance. This study considered four types of base fluids including water, ethylene glycol (EG), oil, and glycerin with 2% volume fraction of diamond nanoparticle, and four types of MCHS substrate materials including copper, aluminium, steel, and titanium. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using the finite volume method. It is found that the best uniformities in heat transfer coefficient and temperature among the four mixture flows can be obtained using glycerin-base nanofluid followed by oil-base nanofluid, EG-base nanofluid, and water-base nanofluid heat sinks. However, the heat transfer performance of water-base nanofluid can be greatly enhanced in steel made substrate heat sink.     

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.     

On heat transfer in external natural convection flows using two nanofluids

In the present work, a theoretical model based on the integral formalism approach for both laminar and turbulent external natural convection is extended to nanofluids. By using empirical models based on experimental data for computing viscosity and thermal conductivity of water–alumina and water–CuO suspensions, a close attention is first focused on the influence due to increasing the volume fraction of nanoparticles on the heat transfer and then to the transition threshold between laminar and turbulent regimes. The heat transfer is shown to strongly depend on the flow regime and on particle volume fraction. A clear degradation of heat transfer is observed using nanofluids while compared to that of the base-fluid. Moreover, the fact of increasing the particle volume fraction tends to delay the occurrence of the flow transition to turbulence.     

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.     

Numerical study of convective heat transfer of nanofluids in a circular tube two-phase model versus single-phase model

Laminar convective heat transfer of nanofluids in a circular tube under constant wall temperature condition is studied numerically using a CFD¹ approach. Single-phase and two-phase models have been used for prediction of temperature, flow field, and calculation of heat transfer coefficient. Effects of some important parameters such as nanoparticle sources, nanoparticle volume fraction and nanofluid Peclet number on heat transfer rate have been investigated. The results of CFD simulation based on two-phase model were used for comparison with single-phase model, theoretical models and experimental data. Results have shown that heat transfer coefficient clearly increases with an increase in particle concentration. Also the heat transfer enhancement increases with Peclet number. Two-phase model shows better agreement with experimental measurements. For Cu/Water nanofluid with 0.2% concentration, the average relative error between experimental data and CFD results based on single-phase model was 16% while for two-phase model was 8%. Based on the results of the simulation it was concluded that the two-phase approach gives better predictions for heat transfer rate compared to the single-phase model.     

Numerical simulation of turbulent natural convection of nanofluid with thermal radiation inside a tall enclosure under the influence of magnetohydrodynamic

In the present study, the natural convective heat transfer in the turbulent flow of water/CuO nanofluid with volumetric radiation and magnetic field inside a tall enclosure has been numerically investigated. The thermophysical properties of nanofluid have been considered variable with temperature and the effects of Brownian motion of nanoparticles have been considered. The main objective of this work is an investigation of the effect of using water/CuO nanofluid and presence of magnetic field on turbulent natural convection in three types of enclosures (vertical, inclined, and horizontal) by considering the volumetric radiation. The governing equations on turbulent flow domain under the influence of the magnetic field and by considering the combination of volumetric radiation and natural convection have been solved by a coupled algorithm. For validating the present research, a comparison has been carried out with the laminar natural convection flow under the influence of the magnetic field and radiation effects and also, the natural turbulent convection flow of previous studies and a proper coincidence has been achieved. The results indicated that by increasing volume fraction and Hartmann number the average Nusselt number enhances and reduces, respectively. By adding 1% CuO nanoparticles to the base fluid, heat transfer improves from 10.59% to 17.05%. However, by increasing the volume fraction from 1% to 4%, heat transfer improves from 1.35% to 4.90%. By increasing Hartmann number from 0 to 600, heat transfer reduces from 9.29% to 22.07%. Also, the results show that the ratio of deviation angle of the enclosure to the horizontal surface has considerable effects on heat transfer performance. Therefore, in similar conditions, the inclined enclosure with a deviation angle of 45° compared to the vertical and horizontal enclosure has better thermal performance.     

Numerical investigation of effective parameters in convective heat transfer of nanofluids flowing under a laminar flow regime

This article presents a numerical investigation on heat transfer performance and pressure drop of nanofluids flows through a straight circular pipe in a laminar flow regime and constant heat flux boundary condition. Al₂O₃, CuO, carbon nanotube (CNT) and titanate nanotube (TNT) nanoparticles dispersed in water and ethylene glycol/water with particle concentrations ranging between 0 and 6 vol.% were used as working fluids for simulating the heat transfer and flow behaviours of nanofluids. The proposed model has been validated with the available experimental data and correlations. The effects of particle concentrations, particle diameter, particles Brownian motions, Reynolds number, type of the nanoparticles and base fluid on the heat transfer coefficient and pressure drop of nanofluids were determined and discussed in details. The results indicated that the particle volume concentration, Brownian motion and aspect ratio of nanoparticles similar to flow Reynolds number increase the heat transfer coefficient, while the nanoparticle diameter has an opposite effect on the heat transfer coefficient. Finally, the present study provides some considerations for the appropriate choice of the nanofluids for practical applications.     

Analysis of microchannel heat sink performance using nanofluids

In this study, silicon microchannel heat sink performance using nanofluids as coolants was analyzed. The nanofluid was a mixture of pure water and nanoscale Cu particles with various volume fractions. The heat transfer and friction coefficients required in the analysis were based on theoretical models and experimental correlations. In the theoretical model, nanofluid was treated as a single-phase fluid. In the experimental correlation, thermal dispersion due to particle random motion was included. The microchannel heat sink performances for two specific geometries, one with W_ch = W_fin = 100 μm and L_ch = 300 μm, the other with W_ch = W_fin = 57 μm and L_ch = 365 μm, were examined. Because of the increased thermal conductivity and thermal dispersion effects, it was found that the performances were greatly improved for these two specific geometries when nanofluids were used as the coolants. In addition to heat transfer enhancement, the existence of nanoparticles in the fluid did not produce extra pressure drop because of small particle size and low particle volume fraction.     

Experimental investigation of nanofluids in confined laminar radial flows

This paper presents an experimental investigation of heat transfer enhancement capabilities of coolants with suspended nanoparticles (Al₂O₃ dispersed in water) inside a radial flow cooling device. Steady, laminar radial flow of a nanofluid between a heated disk and a flat plate with axial coolant injection has been considered. An experimental test rig was built. Results show that heat transfer enhancements are possible in radial flow cooling systems with the use of nanofluids. In general, it was noticed that the Nusselt number increases with particle volume fraction and Reynolds number and decreases with an increase in disk spacing.     

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.