Orthotropic Thermal Conductivity Effect on Cylindrical Pin Fin Heat Transfer

2005 ◽  
Author(s):  
Raj Bahadur ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
High Performance ◽  
Heat Sinks ◽  
Transfer Coefficients ◽  
Design And Optimization ◽  
Pin Fin ◽  
Wide Range ◽  
Pin Fins ◽  
The One

There is growing interest in the use of polymer composites with enhanced thermal conductivity for high performance fin arrays and heat sinks. However, the thermal conductivity of these materials is relatively low compared to conventional fin metals, and strongly orthotropic. Therefore, the design and optimization of such polymer pin fins requires extension of the one dimensional classical fin analysis to include two-dimensional orthotropic heat conduction effects. An analytical equation for heat transfer from a cylindrical pin fin with orthotropic thermal conductivity is derived and validated using detailed finite-element results. The thermal performance of such fins was found to be dominated by the axial thermal conductivity, but to depart from the classical fin solution with increasing values of a radius- and radial conductivity-based Biot number. Using these relations, it is determined that fin orthotropy does not materially affect the behavior of typical air-cooled fins. Alternatively, for heat transfer coefficients achievable with water cooling and conductivity ratios below 0.1, the fin heat transfer rate can fall more than 25% below the “classical” heat transfer rates. Detailed orthotropic fin temperature distributions are used to explain this discrepancy. Simplified orthotropic pin fin heat transfer equations are derived and validated over a wide range of orthotropic conditions.

scholarly journals Experimental and Numerical Examinations of Temperature Distributions along SSF Pin Fins Cast through Semisolid Materials Processing

2019 ◽  
Vol 8 (12) ◽  
pp. 500-503
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Stainless Steel ◽  
Heat Sinks ◽  
Materials Processing ◽  
Length Scale ◽  
Pin Fin ◽  
Temperature Distributions ◽  
Pin Fins ◽  
Enhancing Heat Transfer

Heat sinks or fins stand deployed for enhancing heat transfer. That’s why, planned experiments remain fortified for examining the impacts of SSF pin fin on thermal dispersal concerning constant thermal value 6 W/cm2 . For that five chromel-alumel thermocouples are preferred, above and beyond, SSF pin fins materials of stainless steel and aluminum. As anticipated, for both the stated SSF pin fins, temperature declines for increasing length scale. Besides, both results are comparable with each other. However, temperature distributions over SSF aluminum pin fin declines relatively at faster rate comparable to that over SSF stainless steel pin fin. Obviously, it may be owing to higher thermal conductivity of SSF aluminum pin fin. Therefore, it carries superior, pleasant and momentous thermal performances.

scholarly journals Numerical Research on Thermal Variations along SSF Pin Fins Shaped with SSM Processing

2019 ◽  
Vol 8 (12) ◽  
pp. 504-507
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Stainless Steel ◽  
Heat Dissipation ◽  
Heat Sinks ◽  
Pin Fin ◽  
Temperature Distributions ◽  
Pin Fins ◽  
Numerical Research

Fins or heat sinks are meant for boosting heat transfer. Therefore, planned computations remain fortified for examining the impacts of SSF pin fin on thermal dispersal concerning constant thermal value 6 W/cm2 . For that SSF pin fins materials of stainless steel and aluminum are preferred. Usual convective equations are solved to foretell thermal apprehensions. As anticipated, for both the stated SSF pin fins, temperature and heat flux declines for increasing length scales. Additionally, temperature distributions on SSF aluminum pin fin lays beneath SSF stainless steel pin fin. Hence, heat dissipation from SSF aluminum pin fin is relatively higher. Obviously, it may be owing to quite higher thermal conductivity of SSF aluminum pin fin. Consequently, it delivers higher, gregarious and remarkable thermal behaviors. Nevertheless, both simulation forecasts remain analogous with one another.

Hydoroil-Based Micro Pin Fin Heat Sink

2006 ◽  
Author(s):  
Ali Kosar ◽  
Chih-Jung Kuo ◽  
Yoav Peles
Keyword(s):  
Heat Sink ◽  
Hydraulic Performance ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Pin Fins ◽  
Micro Pin Fins

An experimental study on thermal-hydraulic performance of de-ionized water over a bank of shrouded NACA 66-021 hydrofoil micro pin fins with wetted perimeter of 1030-μm and chord thickness of 100 μm has been performed. Average heat transfer coefficients have been obtained over effective heat fluxes ranging from 4.0 to 308 W/cm2 and mass velocities from 134 to 6600 kg/m2s. The experimental data is reduced to the Nusselt numbers, Reynolds numbers, total thermal resistances, and friction factors in order to determine the thermal-hydraulic performance of the heat sink. It has been found that prodigious hydrodynamic improvement can be obtained with the hydrofoil-based micro pin fin heat sink compared to the circular pin fin device. Fluid flow over pin fin heat sinks comprised from hydrofoils yielded radically lower thermal resistances than circular pin fins for a similar pressure drop.

Heat Transfer Enhancement by Fins in the Microscale Regime

1999 ◽  
Vol 121 (4) ◽  
pp. 972-977 ◽  
Author(s):  
F.-C. Chou ◽  
J. R. Lukes ◽  
C.-L. Tien
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Size Effect ◽  
Heat Transfer Enhancement ◽  
Transfer Enhancement ◽  
Pin Fin ◽  
Pin Fins ◽  
Microscale Effect ◽  
Fin Thickness ◽  
Micro Pin Fins

The current literature contains many studies of microchannel and micro-pin-fin heat exchangers, but none of them consider the size effect on the thermal conductivity of channel and fin walls. The present study analyzes the effect of size (i.e., the microscale effect) on the microfin performance, particularly in the cryogenic regime where the microscale effect is often appreciable. The size effect reduces the thermal conductivity of microchannel and microfin walls and thus reduces the heat transfer rate. For this reason, heat transfer enhancement by microfins becomes even more important than for macroscale fins. The need for better understanding of heat transfer enhancement by microfins motivates the current study, which resolves three basic issues. First, it is found that the heat, flow choking can occur even in the case of simple plate fins or pin fins in the microscale regime, although choking is usually caused by the accommodation of a cluster of fins at the fin tip. Second, this paper shows that the use of micro-plate-fin arrays yields a higher heat transfer enhancement ratio than the use of the micro-pin-fin arrays due to the stronger reduction of thermal conductivity in micro-pin-fins. The third issue is how the size effect influences the fin thickness optimization. For convenience in design applications, an equation for the optimum fin thickness is established which generalizes the case without the size effect as first reported by Tuckerman and Pease.

Single-Phase Heat Transfer in Mems-Based Pin Fin Heat Sink

2005 ◽  
Author(s):  
Ali Kosar ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Pin Fins ◽  
Micro Pin Fins

An experimental study has been performed on single-phase heat transfer of de-ionized water over a bank of shrouded micro pin fins 243-μm long with hydraulic diameter of 99.5-μm. Heat transfer coefficients and Nusselt numbers have been obtained over effective heat fluxes ranging from 3.8 to 167 W/cm2 and Reynolds numbers from 14 to 112. The results were used to derive the Nusselt numbers and total thermal resistances. It has been found that endwalls effects are significant at low Reynolds numbers and diminish at higher Reynolds numbers.

Heat Transfer in a Rib and Pin Roughened Rotating Multi-Pass Channel With Hub Turning Vane and Trailing-Edge Slot Ejection

2015 ◽  
Author(s):  
Hao-Wei Wu ◽  
Hootan Zirakzadeh ◽  
Je-Chin Han ◽  
Luzeng Zhang ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Side Wall ◽  
Internal Cooling ◽  
Test Model ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
The Third ◽  
Pin Fins ◽  
Cooling Air

A three-passage internal cooling test model with a 180° U-bend at the hub turn portion was used to perform the investigation. The flow is radially inward at the second passage, while it is radially outward at the third passage after the U-bend. Measurement was conducted at the second and the third passages. Aspect ratio of the second passage is 2:1 (AR=2), while the third passage is wedge-shaped with side wall slot ejections. The squared ribs with P/e = 8, e/Dh = 0.1, α = 45°, were configured on both leading and trailing surfaces along the second passage, and also the inner half of the third passage. Three rows of cylinder-shaped pin-fins with diameter of 3 mm were placed at both leading and trailing surfaces of the outer half of the third passage. The results showed that the rotating effects on radial inward flow and radial outward flow are consistent with previous studies. When there is no turning vane, heat transfer on the leading surface at hub turn region is increased by rotation, while it is decreased on the trailing surface. The presence of turning vane reduces the effect of rotation on hub turn portion. Ejection and pin-fin array enhance heat transfer at the third passage. Even though there is mass loss of cooling air along the third passage with side wall slot ejection, the heat transfer coefficient remains high until the end of the passage. Correlation between regional heat transfer coefficients and rotation numbers is presented for both cases of with and without turning vane.

Cryogenic Single-Phase Heat Transfer in a Microscale Pin Fin Heat Sink

2013 ◽  
Author(s):  
Eric D. Truong ◽  
Erfan Rasouli ◽  
Vinod Narayanan
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
Single Phase ◽  
Flow Direction ◽  
Heat Sinks ◽  
Variable Cross ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients

A combined experimental and computational fluid dynamics study of single-phase liquid nitrogen flow through a microscale pin-fin heat sink is presented. Such cryogenic heat sinks find use in applications such as high performance computing and spacecraft thermal management. A circular pin fin heat sink in diameter 5 cm and 250 micrometers in depth was studied herein. Unique features of the heat sink included its variable cross sectional area in the flow direction, variable pin diameters, as well as a circumferential distribution of fluid into the pin fin region. The stainless steel heat sink was fabricated using chemical etching and diffusion bonding. Experimental results indicate that the heat transfer coefficients were relatively unchanged around 2600 W/m2-K for flow rates ranging from 2–4 g/s while the pressure drop increased monotonically with the flow rate. None of the existing correlations in literature on cross flow over a tube bank or micro pin fin heat sinks were able to predict the experimental pressure drop and heat transfer characteristics. However, three dimensional simulations performed using ANSYS Fluent showed reasonable (∼7 percent difference) agreement in the average heat transfer coefficients between experiments and CFD simulations.

An Experimental Study of Pin Fin Heat Sinks and Determination of End Wall Heat Transfer

2003 ◽  
Author(s):  
Massimiliano Rizzi ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Sink ◽  
Optimization Methods ◽  
Heat Sinks ◽  
Base Region ◽  
Transfer Coefficients ◽  
Media Type ◽  
Pin Fin ◽  
Heat Transfer Coefficients

An experimental study of a pin fin heat sink was carried out in support of the development of heat sink optimization methods requiring more detailed measurements be made. Measurements of heat flux and temperature are used to separately determine heat transfer coefficients for the pins and the base region between the pins. Three pitch to diameter ratios (distance from pin center to pin center measured diagonally) were studied: P/d = 3/1, 9/4, 3/2. Heat generation was accomplished using cartridge heaters inserted into a copper block. The high thermal conductivity of the copper ensured that the surface beneath the heat sink would be at a constant temperature. The cooling fluid was air and the experiments were conducted with a Reynolds numbers based on a porous media type hydraulic diameter ranging from 500 to 25000. The channel had a shroud that touches the fin tips, eliminating any flow bypass. The pin surface heat transfer coefficients match the values reported by Kays and London and by Zukauskas. The base region heat transfer coefficients were, surprisngly, larger than the pin values.

scholarly journals Experimental analysis of parallel plate and crosscut pin fin heat sinks for electronic cooling applications

2010 ◽  
Vol 14 (1) ◽  
pp. 147-156 ◽  
Author(s):  
Harish Sivasankaran ◽  
Godson Asirvatham ◽  
Jefferson Bose ◽  
Bensely Albert
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Parallel Plate ◽  
Electronic Cooling ◽  
Heat Sinks ◽  
Average Heat Transfer Coefficient ◽  
Average Heat ◽  
Pin Fin ◽  
Pin Fins

Experimental investigation of parallel plate fin and the crosscut pin fin heat sinks where the heating element placed asymmetrically is performed. Theoretical calculations were done and compared with the experimental results. A comparative study was made based on their efficiencies, heat transfer coefficient, and the thermal performance. From the experimental results it was found that the average heat transfer coefficient of parallel plate fins is higher than that of crosscut pin fins with many perforations. However the performance efficiency of both the crosscut pin fins and parallel plate fins is similar. A hybrid approach was employed to significantly optimize the distance between the fan and heat sink for parallel plate and crosscut pin fins. Parallel plate heat sink with an average heat transfer coefficient of 46 W/m?K placed at an optimum fan distance of 40-60 mm is selected as the suitable choice for the micro-electronic cooling when the heating element is placed asymmetrically.

scholarly journals DETERMINING OF PARAMETERS OF HEAT EXCHANGE FOR VAPORIZATION OF THE MIXED REFRIGERANT ON THE HIGH THERMAL CONDUCTIVITY SINTERED POWDER CAPILLARY-POROUS COATINGS

2018 ◽  
Vol 61 (1) ◽  
pp. 70-79 ◽  
Author(s):  
A. V. Ovsyannik ◽  
E. N. Makeeva
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Exchange ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
High Thermal Conductivity ◽  
Porous Coating ◽  
Transfer Coefficients ◽  
Porous Coatings ◽  
Wide Range

The results of experimental research of heat exchange under the nucleate boiling of refrigerants R404a, R407c and R410a on the tubes with capillary-porous coating are presented. Experimental studies were carried out with the aid of an experimental installation in conditions of a large volume at pressures of saturation pн = 0.9–1.4 MPa and densities of the heat flux q = 5–35 kW/m2. For the first time the criterion equation for the calculation of the intensity of heat transfer during evaporation of ozone safe refrigerants on surfaces with high thermal conductivity sintered capillary-porous coating was obtained. Experimental data are summarized satisfactorily in a wide range of parameters of the porous layer, i.e. the pressure (pн = 0.9–1.4 MPa) and heat loads (q = 5–35 kW/m2). The ratio makes us possible to calculate the heat transfer coefficients within ±20 %. The dependence can be used in engineering calculations of the characteristics of the heat exchangers of the evaporative type. The coefficient of heat transfer during boiling of refrigerants on the investigated surfaces with the sintered capillary-porous coating, 4 times higher than on a smooth one and 1.5 times higher than on the finned surface, that allows us to come to a conclusion about the advantage of porous coatings. Boiling in capillary-porous coating leads to a decrease in weight and size of the installations due to the heat exchange intensification and the size of the tubes smaller as compared to the size of the finned ones.

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