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TECHNICAL PAPERS: Micro/Nanoscale Heat Transfer

Thermal Analysis of Micro-Column Arrays for Tailored Temperature Control in Space

[+] Author and Article Information
M. Adjim

Département d’Hydraulique, Faculté des Sciences de l’Ingénieur, Université Abou-Bekr Belkaid de Tlemcen, Zemcen 13000, Algeria

R. Pillai

Physics and Electrical and Computer Engineering Departments, Texas Center for Advanced Materials, University of Houston, 724 S&R Building 1, Houston, TX 77004

A. Bensaoula1

Physics and Electrical and Computer Engineering Departments, Texas Center for Advanced Materials, University of Houston, 724 S&R Building 1, Houston, TX 77004bens@uh.edu

D. Starikov, C. Boney

 Integrated Micro Sensors, Inc., 10814 Atwell Drive, Houston, TX 77096

A. Saidane

Département de Génie Electrique, ENSET d’Oran, B.P. 1523, M’Naouer-Oran 1523, Algeria

1

Corresponding author.

J. Heat Transfer 129(7), 798-804 (Aug 14, 2006) (7 pages) doi:10.1115/1.2717246 History: Received February 02, 2006; Revised August 14, 2006

Lightweight yet precise, temperature control protocols are critical in a variety of applications. This is especially true in space where weight and volume are at a premium and reliability is paramount. In space, complex processes to manage the heat fluxes generated from within and absorbed from space by the spacecraft are usually implemented. Surfaces having different heat fluxes might need to be controlled separately and maintained at different temperatures. The work presented in this paper evaluates a novel laser surface modification process to form micro-column arrays (MCA) on any material for use as highly adaptive radiators. The MCA-structured surfaces have experimentally been shown to have excellent emissive properties. Finite element methods have been used to simulate the temperature profiles for surfaces with and without MCA compared to pin fin structures as a function of input heat flux density. In the case of Ti, our models show that pin fin arrays are better heat radiating surfaces than equivalent MCA structures with cone-like profiles. Such structures, however, are difficult to modify and usually require complicated and expensive fabrication processes. Overall, MCA structures are shown to allow good control over base surface temperature for varying heat fluxes and different MCA aspect ratios. For Ti, under steady state conditions, an aspect ratio of 12 has been shown to be optimal for surface heat reduction. Preliminary experimental results show that the temperature drop is inline with that theoretically predicted.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Plots of reflectance measurements for MCA processed and unprocessed Alloy 321, Hastelloy C276, and tantalum. The values of α provided correspond to the absorptivity integrated over the entire measurement range for the three MCA structured samples. (b) Ratios of the relative normalized spectral emission from Alloy321 to a blackbody spectrum and Hastelloy C276 to a blackbody spectrum at 1073K, the linear portion indicating the optical emission curves are similar.

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Figure 2

Experimental setup for measuring temperature characteristics of MCA sample

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Figure 3

(a) Top view schematic of an array of micro-cones representing an actual surface with MCA. (b) 3D schematic describing the boundary conditions for the model, indicating the surface-to-surface radiation and surface-to-ambient radiation boundaries. Groups 4 and 5 are the surfaces equivalent to groups 2 and 3 on the upper right and upper left of the figure, respectively.

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Figure 4

Simulations carried out on the MCA model of aspect ratios 12.4, with outer boundary conditions set as surface-to-ambient as in previous models, compared to MCA model with coupled boundary conditions

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Figure 5

Simulations of different extended surface structures on a 40μm×40μm surface of titanium subjected to a heat flux of 4W∕cm2 showing the individual steady-state temperatures. A temperature decrease of 176K based on MCAs and 265K based on the rectangular cross-section pin fin arrays is observed.

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Figure 6

(a) Simulations carried out on the MCA model of different aspect ratios fabricated on Ti, showing temperature reduction (ΔT) of the base for a wide range of heat fluxes at different aspect ratios. Saturation is shown to occur for an AR ∼12. (b) Plot of the same data in Fig. 8 to indicate the temperature reduction (ΔT) of the base surface with applied heat flux.

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Figure 7

Plot of temperature versus heat flux for Alloy 321 MCA (aspect ratio of ∼5.4) structured and flat foils. For the MCA structured surface we have plotted the temperature versus heat flux for a second thermal cycle.

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Figure 8

Comparison of experimentally observed decrease in temperature versus simulated results on Alloy321 using different models. The macroscopic model includes conduction heat loss due to the feedthrough rods but does not account for heating due to radiation reflected from the vacuum chamber, while the simplified four cone MCA model only includes heat loss due to radiation.

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