Research Papers: Porous Media

Direct Simulation of Thermal Transport Through Sintered Wick Microstructures

[+] Author and Article Information
Karthik K. Bodla, Jayathi Y. Murthy, Suresh V. Garimella

 Cooling Technologies Research Center, an NSF IUCRC, School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907-2088

J. Heat Transfer 134(1), 012602 (Nov 29, 2011) (10 pages) doi:10.1115/1.4004804 History: Received January 17, 2011; Revised July 27, 2011; Published November 29, 2011; Online November 29, 2011

Porous sintered microstructures are critical to the functioning of passive heat transport devices such as heat pipes. The topology and microstructure of the porous wick play a crucial role in determining the thermal performance of such devices. Three sintered copper wick samples employed in commercial heat pipes are characterized in this work in terms of their thermal transport properties––porosity, effective thermal conductivity, permeability, and interfacial heat transfer coefficient. The commercially available samples of nearly identical porosities (∼61% open volume) are CT scanned at 5.5 μm resolution, and the resulting image stack is reconstructed to produce high-quality finite volume meshes representing the solid and interstitial pore regions, with a conformal mesh at the interface separating these two regions. The resulting mesh is then employed for numerical analysis of thermal transport through fluid-saturated porous sintered beds. Multiple realizations are employed for statistically averaging out the randomness exhibited by the samples under consideration. The effective thermal conductivity and permeability data are compared with analytical models developed for spherical particle beds. The dependence of effective thermal conductivity of sintered samples on the extent of sintering is quantified. The interfacial heat transfer coefficient is compared against a correlation from the literature based on experimental data obtained with spherical particle beds. A modified correlation is proposed to match the results obtained.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

(a) Top view of a 250–355 μm sample, (b) scan image in side view, showing the substrate and the sintered regions (sintered region highlighted). Scan images for (c) a 45–75 μm sample and (d) a 106–150 μm sample are also shown.

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Figure 2

Image processing and meshing showing (a) original image with region of interest identified, (b) segmented image, and (c) image after surface/volume reconstruction. (The red regions indicate voids in the particles.)

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Figure 3

(a) Sintered copper and (b) surrounding pore space. An inset of mesh for a 250–355 μm sample is also shown.

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Figure 4

Boundary conditions for (a) conjugate conduction problem and (b) flow problem

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Figure 5

Temperature contours for conduction in a 250–355 μm subsample

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Figure 6

Particles identified by color in a 250–355 μm subsample

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Figure 7

Effective thermal conductivity as a function of necking ratio with air and water as the saturating liquids

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Figure 8

Effective thermal conductivity as a function of porosity. In the present computations, ksolid , kwater , and kair are 387.5, 0.613, and 0.0265 W/m.K, respectively.

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Figure 9

Pressure drop variation with modified inlet velocity. Representative values for a subsample for each of the three samples considered in this work are shown.

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Figure 10

Variation of friction factor with Reynolds number. The present calculations are compared with results from the literature [12].

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Figure 11

Representative streamtraces and temperature contours in a 250–355 μm subsample for forced convection through the sintered particle bed. An inset of the punctured particle is also shown.

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Figure 12

Nusselt number as a function of Reynolds number. The present computations and proposed correlations are compared with the Wakao and Kaguei correlation (Eq. 21) [15].



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