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In this paper, different heat sinks are investigated to improve CPU cooling experimentally. Different types of copper heat sinks including a novel "porous heat sink" are proposed and compared to obtain the optimum heat transfer rate. Water and Al2O3/water nanofluids (40 nm) in two different volume fractions (0.1 and 0.2 vol.% from 40-nm nanoparticles) are used as heat transfer fluid to cool the CPU. Different flow rates are also examined in the experimental study. The Nusselt number, wall temperature, thermal resistance and LMTD temperature have been analyzed for a wide range of parameters of the heat sinks. Also, the effect of geometry, heat transfer fluid, input power and flow rate on the heat transfer rate is reported. The result shows that the geometry of the heat sink has an important effect on the thermal performance of the system. The rate of heat transfer in the proposed novel porous heat sink is larger than the other cases. The Nusselt number in the porous heat sink by using nanofluids is 2.2 times larger than the heat sink with an inline pattern. [ABSTRACT FROM AUTHOR]

In this article, the effects of dependent parameters such as inlet Reynolds number (4000 ≤ Re ≤ 20,000), nozzle-plate distance (4 ≤ H/D ≤ 10), plate diameter (18 < D/B < 40 based on other approaches), inlet flow type (fully developed, uniform and pulsed) and thermal boundary condition (constant heat flux and temperature) in confined and unconfined turbulent impinging jet are investigated considering constant inlet fluid (air). The obtained results are compared with other experimental and numerical results found in the literature. This investigation indicates that the $$k - \omega - \overline{{v^{2} }} - f$$ model acquires appropriate performance in terms of thermal and dynamical fluid analysis compared to other turbulence models and experimental results. [ABSTRACT FROM AUTHOR]

Natural convection in an open end cavity with a hot inclined wall is simulated based on the lattice Boltzmann method (LBM). The physics of flow and energy transfer in open end cavities are addressed when the hot wall is inclined. The combination of the two topics (open cavity and inclined walls) is the main novelty of the present study. The effects of the angle of the hot inclined wall on the flow field and heat transfer are thoroughly investigated. The Prandtl number is fixed to 0.71 (air). The Rayleigh number and the angle of the hot inclined wall are varied in the range of 10 to 10 and 60° to 85°, respectively. The results are presented for two different aspect ratios, i.e., A = 1 and 2. The results obtained with the LBM are also compared with those of the finite volume method (FVM). The predicted results of the LBM conform to those of the FVM. The results show that by increasing the angle of the hot inclined wall and the aspect ratio of the cavity, the average Nusselt number decreases. The trend of the local Nusselt number on the inclined wall is also discussed. [ABSTRACT FROM AUTHOR]

The main purpose of this study is to investigate the CPU cooling using Alumina and CNT nanofluids and comparing the obtained results with the cooling performance of the common base fluids (water and Ethylene Glycol). The volume fraction of the Alumina/water nanofluid is considered as 0.1, 0.25 and 0.5(%w/w). Moreover, the volume fractions of CNT in the base fluid are 0.1 and 0.25 (%w/w). The Ethylene Glycol with the volume percent of 30% and 50% have been also employed for the cooling process. Experiments have been carried out for different flow rates. The averaged convection heat transfer coefficients as well as final processor temperatures have been reported for a wide range of parameters. The experimental results along with the confidence intervals are reported. Results show a 4% increase in the convection heat transfer coefficient in the case of Ethylene Glycol (30%). An increase of 6% is also reported by using 0.5% volume fraction of Alumina nanofluid. The best heat transfer enhancement (about 13%) is related to CNT nanofluids with the volume fraction of 0.25% for the flow rate of 21 mL/s. [ABSTRACT FROM AUTHOR]

In this study, the immersed boundary-thermal lattice Boltzmann method has been used to simulate non-Newtonian fluid flow over a heated circular cylinder. The direct-forcing algorithm has been employed to couple the off-lattice obstacles and on-lattice fluid nodes. To investigate the effect of boundary sharpness, two different diffuse interface schemes are considered to interpolate the velocity and temperature between the boundary and computational grid points. The lattice Boltzmann equation with split-forcing term is applied to consider the effects of the discrete lattice and the body force to the momentum flux, simultaneously. A method for calculating the Nusselt number based on diffuse interface schemes is developed. The rheological and thermal properties of non-Newtonian fluids are investigated under the different power-law indices and Reynolds numbers. The effect of numerical parameters on the accuracy of the proposed method has been investigated in detail. Results show that the rheological and thermal properties of non-Newtonian fluids in the presence of a heated immersed body can be suitably captured using the immersed boundary thermal lattice Boltzmann method. [ABSTRACT FROM AUTHOR]

Highlights: [•] A porous block is considered in the channel for analysis of non-Newtonian fluids. [•] Both regular and random arrangements of fibers are employed in the channel. [•] The Nusselt number for both arrangements are presented using ‘confidence interval’. [•] Several blockage ratios with different arrangements are checked to obtain a correlation. [•] The method is verified through comparison with existing results. [Copyright &y& Elsevier]

The main goal of the present study is to investigate the heat transfer enhancement in a channel partially filled with an anisotropic porous block (Porous Foam) using the lattice Boltzmann method (LBM). Combined pore level simulation of flow and heat transfer is performed for a 2D channel which is partially filled with square obstacles in both ordered and random arrangements by LBM which is not studied completely in the literature. The effect of the Reynolds number, different arrangements of obstacles, blockage ratio and porosity on the velocity and temperature profiles inside the porous region are studied. The local and averaged Nusselt numbers on the channel walls along with the respective confidence interval and comparison between results of regular and random arrangements are presented for the first time. For constant porosity and block size, the maximum value of averaged Nusselt number in the porous block is obtained in the case of random arrangement of obstacles. Also, by decreasing the porosity, the value of averaged Nusselt number is increased. Heat transfer to the working fluids increases significantly by increasing the blockage ratio. Several blockage ratios with different arrangements are checked to obtain a correlation for the Nusselt number. [ABSTRACT FROM AUTHOR]

This article is concerned with the effects of flow and migration of nanoparticles on heat transfer in a straight channel occupied with a porous medium. Investigation of force convective heat transfer of nanofluids in a porous channel has not been considered completely in the literature and this challenge is generally considered to be an open research topic that may require more study. The fully developed flow and steady Darcy-Brinkman-Forchheimer equation is employed in porous channel. The thermal equilibrium model is assumed between nanofluid and solid phases. It is assumed that the nanoparticles are distributed non-uniformly inside the channel. As a result the volume fraction distribution equation is also coupled with governing equations. The effects of parameters such as Lewis number, Schmidt number, Brownian diffusion, and thermophoresis on the heat transfer are completely studied. The results show that the local Nusselt number is decreased when the Lewis number is increased. It is observed that as the Schmidt number is increased, the wall temperature gradient is decreased and as a consequence the local Nusselt number is decreased. The effects of Lewis number, Schmidt number, and modified diffusivity ratio on the volume fraction distribution are also studied and discussed. [ABSTRACT FROM AUTHOR]

In this article, free convection heat transfer over a vertical cylinder with variable surface temperature distributions in a porous medium is analyzed. It is assumed that the fluid and solid phases are not in local thermal equilibrium and, therefore, a two-temperature model of heat transfer is applied. The coupled momentum and energy equations are presented and then they are transformed into ordinary differential equations. The similarity equations are solved numerically. The resulting velocity, streamlines, temperature distributions for fluid and solid phases are shown for different values of parameters entering into the problem. The calculated values of the local Nusselt numbers for both solid and fluid phases are also shown. [ABSTRACT FROM AUTHOR]

Turbulent flow convective heat transfer and friction factor characteristics of Al2O3/water nanofluid flowing inside a uniformly heated horizontal circular tube are conducted in this Letter. To do this, Al2O3 nanoparticles of 40 nm size were characterised and dispersed in distilled water to form stable suspension containing 0.1, 0.5, 1.0, 1.5 and 2.0% volume concentrations of nanofluids. Results indicate that heat transfer coefficients increase with nanofluid volume concentration and do not change with Reynolds number. The enhancement of the Nusselt number is about 22% at Re=13 500 using 2% alumina nanoparticles compared to distilled water. Experimental results are also compared with the existing correlations of convective heat transfer coefficient and pressure drop in turbulent regime. The measured pressure loss when using nanofluids is almost equal to that of the base fluid. [ABSTRACT FROM AUTHOR]

This article is concerned with thermal non-equilibrium (TNE) free convection in a two-dimensional porous enclosure. The Darcy model is used for the momentum equation and it is assumed that a substantial temperature difference exists between solid and fluid phases. Numerical solutions of the governing equations are obtained for a wide range of the governing parameters. The Nusselt numbers for both solid and fluid phases are calculated for a wide range of Rayleigh number, i.e., 500 ≤ Ra ≤ 1500. The effects of the cavity dimensions as well as the fluid-to-solid conductivity ratio on the Nusselt number are also studied. The results of the presented study are compared with those of thermal equilibrium model. Moreover, the results are compared with major computational models presented in the literatures. The results obtained for the Nusselt number in the case of TNE model are correlated with a function incorporating the effects of effective non-dimensional parameters. [ABSTRACT FROM AUTHOR]

This paper is concerned with the conduction heat transfer between two parallel plates filled with a porous medium with uniform heat generation under a nonequilibrium condition. Analytical solution is obtained for both fluid and solid temperature fields at constant porosity incorporating the effects of thermal conductivity ratio, porosity, and a nondimensional heat transfer coefficient at pore level. The two coupled energy equations for the case of variable porosity condition are transformed into a third order ordinary equation for each phase, which is solved numerically. This transformation is a valuable solution for heat conduction regime for any distribution of porosity in the channel. The effects of the variable porosity on temperature distribution are shown and compared with the constant porosity model. For the case of the exponential decaying porosity distribution, the numerical results lead to a correlation incorporating conductivity ratio and interstitial heat transfer coefficient. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an experimental study of convective heat transfer and pressure drop of turbulent flow of TiO2-water nanofluid through a uniformly heated horizontal circular tube has been performed. The spherical TiO2 nanoparticles with a nominal diameter of 15nm are functionalized by a new chemical treatment and then dispersed in distilled water to form stable suspensions containing 0.1, 0.5, 1.0, 1.5 and 2.0% volume concentrations of nanoparticles. Results indicate that heat transfer coefficients increase with increasing the nanofluid volume fraction and it is not changed with altering the Reynolds number. The enhancement of the Nusselt number is about 8% for nanofluid with 2.0% nanoparticle volume fraction at Re=11,800. [Copyright &y& Elsevier]