Height Effect on Heat-Transfer Characteristics of Aluminum-Foam Heat Sinks

2005 ◽  
Vol 128 (6) ◽  
pp. 530-537 ◽  
Author(s):  
W. H. Shih ◽  
W. C. Chiu ◽  
W. H. Hsieh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Temperature Difference ◽  
Thermal Equilibrium ◽  
Aluminum Foam ◽  
Heated Surface ◽  
Heat Sinks ◽  
Local Thermal Equilibrium ◽  
Cooling Air

This study investigates and demonstrates the two conflicting effects of the height on the cooling performance of aluminum-foam heat sinks, under the impinging-jet flow condition. In addition, the nonlocal thermal equilibrium phenomena are also investigated. When the H∕D (the height to diameter ratio) of the aluminum-foam heat sinks is reduced from 0.92 to 0.15, the Nusselt number of aluminum-foam heat sinks is found to first increase and then decrease. The increase in the Nusselt number is caused by the increased percentage of the cooling air reaching the top surface of the waste-heat generation block, resulting from the reduced flow resistance. The decrease in the Nusselt number is mainly caused by the reduction in the heat-transfer area between the cooling air and the solid phase of the aluminum-foam heat sink. As the porosity and pore density decrease, the Nusselt number increases and the convective heat transfer is enhanced. The correlation between the Nusselt and Reynolds numbers for each of the 15 samples studied in this work is reported. For samples with a H∕D>0.31, the temperature difference between the solid and gas phases of aluminum-foam heat sinks decreases with the increase of the distance from the heated surface. The non-local thermal equilibrium regime is observed to exist at low Reynolds number and small dimensionless height. On the other hand, for samples with a H∕D⩽0.31, the temperature difference first increases and then decreases with the increase of the distance from the heated surface; the maximum temperature difference is located at z∕H≒0.25 and is independent of the Reynolds number.

Heat-Transfer Study of Aluminum-Foam Heat Sink for Electronic Cooling

Volume 4 ◽  
2004 ◽  
Author(s):  
W. H. Hsieh ◽  
J. Y. Wu ◽  
W. H. Shih ◽  
W. C. Chiu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Temperature Difference ◽  
Heat Sink ◽  
Thermal Equilibrium ◽  
Aluminum Foam ◽  
Local Thermal Equilibrium ◽  
Pore Density ◽  
Gas Phases ◽  
Non Local

The demand of high speed and miniaturization of electronic components results in increased power dissipation requirement for thermal management. In this work, the effects of porosity (ε), pore density (PPI) and air velocity on the heat-transfer characteristics of aluminum-foam heat sinks are investigated experimentally. The phenomenon of non-local thermal equilibrium (NLTE) is also observed and reported. Results show that the Nu increases as the pore density increases, due to the fact that aluminum foam with a larger pore density has a larger heat-transfer area. The Nusselt number also increases with the increase of porosity due to the same reason. It is noted that temperatures of the solid and gas phases of the aluminum foam decrease as Reynolds number increases, caused by the increased convective heat-transfer rate at higher Reynolds number. The deduced temperature difference between solid and gas phases clearly indicates the existence of non-local thermal equilibrium condition within the aluminum-foam heat sink. The increase of the porosity and the pore density enhances the phenomenon of non-local thermal equilibrium. The temperature difference increases with the decrease of Reynolds number and the distance away from the heat source.

Study of Flow and Heat Transfer Characteristics in Asymmetrically Heated Sintered Porous Heat Sinks With Periodical Baffles

2005 ◽  
Vol 128 (3) ◽  
pp. 226-235 ◽  
Author(s):  
Tzer-Ming Jeng ◽  
Sheng-Chung Tzeng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Sink ◽  
Average Nusselt Number ◽  
Heated Surface ◽  
Heat Sinks ◽  
Heat Transfer Characteristics ◽  
Fluid Medium ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer

This work numerically examined the mechanism of heat transfer in a sintered porous heat sink with baffles. A channel filled with the sintered porous heat sink was asymmetrically heated and metallic baffles were periodically mounted on the heated surface. The fluid medium was air. The results indicate that no recirculation occurred between baffles. The metallic baffle obtained heat from the heated surface by conduction directly from the heated surface and indirectly through the porous media. It dissipated heat to the fluid that passed over the zone above the baffle. The Nusselt numbers in the cases with baffles exceeded those in cases without a baffle. The enhancement in the average Nusselt numbers of sintered porous heat sinks with baffles increased as the Reynolds number (Re) declined; the baffle height (h∕H) increased; the baffle length (w∕H) increased, or the baffle pitch (XL) decreased. However, at Re=500, the average Nusselt number in the case with h∕H=0.3 was higher than those with h∕H=0.7, 0.5, and 0.1. Additionally, the minimum enhancement appeared at around Re=3000 for various h∕H, w∕H, and XL. For the cases with h∕H⩽0.3 and various w∕H as well as XL, at Re>3000, sintered porous heat sinks with baffles insignificantly improved heat transfer.

Efficiency assessment of using graphene nanoplatelets-silver/water nanofluids in microchannel heat sinks with different cross-sections for electronics cooling

2019 ◽  
Vol 30 (1) ◽  
pp. 347-372 ◽  
Author(s):  
Marjan Goodarzi ◽  
Iskander Tlili ◽  
Zhe Tian ◽  
Mohammad Reza Safaei
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Cross Sections ◽  
Graphene Nanoplatelets ◽  
Heat Sinks ◽  
Pumping Power ◽  
Content Type

Purpose This study aims to model the nanofluid flow in microchannel heat sinks having the same length and hydraulic diameter but different cross-sections (circular, trapezoidal and square). Design/methodology/approach The nanofluid is graphene nanoplatelets-silver/water, and the heat transfer in laminar flow was investigated. The range of coolant Reynolds number in this investigation was 200 ≤ Re ≤ 1000, and the concentrations of nano-sheets were from 0 to 0.1 vol. %. Findings Results show that higher temperature leads to smaller Nusselt number, pressure drop and pumping power, and increasing solid nano-sheet volume fraction results in an expected increase in heat transfer. However, the influence of temperature on the friction factor is insignificant. In addition, by increasing the Reynolds number, the values of pressure drop, pumping power and Nusselt number augments, but friction factor diminishes. Research limitations/implications Data extracted from a recent experimental work were used to obtain thermo-physical properties of nanofluids. Originality/value The effects of temperature, microchannel cross-section shape, the volume concentration of nanoparticles and Reynolds number on thermal and hydraulics behavior of the nanofluid were investigated. Results are presented in terms of velocity, Nusselt number, pressure drop, friction loss and pumping power in various conditions. Validation of the model against previous papers showed satisfactory agreement.

Convective Heat Transfer Coefficients in a Building-Integrated Photovoltaic/Thermal System

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Luis M. Candanedo ◽  
Andreas Athienitis ◽  
Kwang-Wook Park
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Average Nusselt Number ◽  
Heated Surface ◽  
Reynolds Numbers ◽  
Building Integrated Photovoltaic ◽  
T System

This paper presents an experimental study for the development of convective heat transfer correlations for an open loop air-based building-integrated photovoltaic/thermal (BIPV/T) system. The BIPV/T system absorbs solar energy on the top surface, which includes the photovoltaic panels and generates electricity while also heating air drawn by a variable speed fan through a channel formed by the top roof surface with the photovoltaic modules and an insulated attic layer. The BIPV/T system channel has a length/hydraulic diameter ratio of 38, which is representative of a BIPV/T roof system for 30–45 deg tilt angles. Because of the heating asymmetry in the BIPV/T channel, two average Nusselt number correlations are reported as a function of Reynolds number: one for the top heated surface and the other for the bottom surface. For the top heated surface, the Nusselt number is in the range of 6–48 for Reynolds numbers ranging from 250 to 7500. For the bottom insulated surface, the Nusselt number is in the range of 22–68 for Reynolds numbers ranging from 800 to 7060. This paper presents correlations for the average Nusselt number as a function of Reynolds number; this correlation is considered adequate for the design of BIPV/T systems where forced convection dominates. Local Nusselt number distributions are also presented for laminar and turbulent flow conditions.

Optimization of the Heat Transfer Rate of Energy Systems of Conductive Bodies Confined to the Center of a Cavity

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Fatma Habbachi ◽  
Fakhreddine S. Oueslati ◽  
Rachid Bennacer ◽  
Afif Elcafsi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Rate ◽  
Temperature Difference ◽  
Transfer Rate ◽  
Numerical Study ◽  
Local Thermal Equilibrium ◽  
Solid Matrix ◽  
Complex Flow ◽  
Flow And Heat Transfer

This paper is a numerical study conducted to investigate the conjugate flow and heat transfer occurring in three-dimensional (3D) natural convection. A cubical enclosure partially filled with porous block (central cubic) and considered in local thermal equilibrium with the fluid. The physical case considered concerns the existence of a horizontal temperature difference across the enclosure, between the left and the right wall, with the other external surfaces being adiabatic. Under these conditions, flow inside the enclosure is generated by the density (temperature) difference across the enclosure and the interaction between the solid porous blocks and the fluid. The Nusselt number on the hot and cold walls is presented to illustrate the overall characteristics of heat transfer consequence of the constrained flow inside the enclosure. The study focuses on the fluid flow and heat transfer evolution versus the dimensionless thickness of the inserted porous layer (0% ≤ η ≤ 100%) and the relative thermal conductivity of the solid matrix to that of the fluid (10−3≤λ̃≤103). The obtained complex flow structure and the corresponding heat transfer (velocity, temperature profiles) are discussed in a steady-state situation. The numerical results are illustrated in terms of isotherms, velocity, streamlines fields, and averaged Nusselt number. Thus, the results of this work can help developing new tools and to optimize the overall heat transfer rate, which is important in many electronic energy components and other energy recovering systems.

scholarly journals Numerical investigation of heat transfer at a rectangular channel with combined effect of nanofluids and swirling jets in a vehicle radiator

2019 ◽  
Vol 23 (6 Part A) ◽  
pp. 3627-3637 ◽  
Author(s):  
Mustafa Kilic ◽  
Asli Abdulvahitoglu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Numerical Investigation ◽  
Average Nusselt Number ◽  
Heated Surface ◽  
Pure Water ◽  
Rectangular Channel ◽  
Turbulent Model ◽  
Swirling Jets

The present study is focused on the numerical investigation of heat transfer from a heated surface by using swirling jets and nanofluids. Consequences of discrete Reynolds number, inlet configuration and types of nanofluids (pure water, Al2O3- -H2O, Cu-H2O, and TiO2-H2O) were studied numerically on heat transfer and fluid-flow. As a base coolant Al2O3-H2O nanofluid was chosen for all parameters. So, a numerical analysis was done by using a k-? turbulent model of PHOENICS CFD code. It is determined that increasing Reynolds number from Re = 12000-21000 causes an increment of 51.3% on average Nusselt Number. Using 1-jet causes an increase of 91.6% and 29.8% on average Nusselt number according to the channel flow and 2-jet. Using Cu-H2O nanofluid causes an increase of 3.6%, 7.6%, and 8.5% on the average Nusselt number with respect to TiO2-H2O, Al2O3-H2O and pure water.

Experimental Investigation of the Heat Transfer Characteristics of Aluminum-Foam Heat Sinks With Restricted Flow Outlet

2007 ◽  
Vol 129 (11) ◽  
pp. 1554-1563 ◽  
Author(s):  
W. H. Shih ◽  
F. C. Chou ◽  
W. H. Hsieh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Generation ◽  
Aluminum Foam ◽  
Heat Sinks ◽  
Pore Density ◽  
Heat Transfer Characteristics ◽  
Measured Velocity ◽  
Transfer Characteristics ◽  
Convective Resistance

This study investigates the heat transfer characteristics of aluminum-foam heat sinks with restricted flow outlets under impinging-jet flow conditions. An annular flow-restricting mask is used to control the height of the flow outlet of the aluminum foam sink, forcing the cooling air to reach the heat-generation surface. The enhanced heat transfer characteristics of aluminum-foam heat sinks using these flow-restricting masks are measured experimentally in this work. The effects of porosity, pore density and length of sample, air velocity, and flow outlet height on the heat transfer characteristics of aluminum-foam heat sinks are investigated. Results show that the effect of the flow outlet height is stronger than that of the pore density, porosity, or height of the aluminum heat sinks studied in this work. A general correlation between the Nusselt number and the Reynolds number based on the equivalent spherical diameter of the aluminum foam is obtained for 32 samples of aluminum-foam heat sinks with different sample heights (20–40mm), pore densities (5–40ppi(pore∕inch)), porosities (0.87–0.96), and flow outlet heights (5–40mm). It should be noted that, based on the measured velocity profile, the increase of the Nusselt number of the aluminum-foam heat sink with the decrease in the flow outlet height is caused by the reduced convective resistance at the solid-gas interface through the increased velocity near the heat-generation surface. The reduction in flow outlet height increases the local thermal nonequilibrium condition near the heat-generation surface.

Hydrodynamic and Thermal Characteristics of Single-Phase and Two-Phase Micro-Pin-Fin Heat Sinks

2007 ◽  
Author(s):  
Abel M. Siu-Ho ◽  
Weilin Qu ◽  
Frank Pfefferkorn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Single Phase ◽  
Thermal Characteristics ◽  
Heat Sinks ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Pin Fin

The pressure drop and heat transfer characteristics of single-phase and two-phase micro-pin-fin heat sinks were investigated experimentally. Fabricated from 110 copper, the heat sink contained an array of 1950 staggered square micro-pin-fins with 200×200 μm2 cross-section by 670 μm height. The ratios of longitudinal pitch and transverse pitch to pin-fin hydraulic diameter are equal to 2. Deionized water was employed as the cooling liquid. A coolant inlet temperature of 30 °C, and six maximum mass velocities, ranging from 183 to 420 kg/m2s, were tested. The corresponding inlet Reynolds number ranged from 45.9 to 105.9. General hydrodynamic and thermal characteristics of the two flow regimes of single-phase flow and flow boiling were described. The measured temperature distribution was used to evaluate single-phase heat transfer coefficient and Nusselt number. Predictions of the previous friction factor and heat transfer correlations that were developed for low Reynolds number (Re<1000) single-phase flow in short pin-fin arrays were compared to the present micro-pin-fin single-phase pressure drop and Nusselt number data, respectively. The Short et al friction factor correlation and the Kos¸ar et al. heat transfer correlation provided acceptable predictions.

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