Natural Convection Air Cooling of a Discrete Heat Source on a Conducting Board in a Shallow Horizontal Enclosure

[+] Author and Article Information
A. Ortega, B. S. Lall

Center for Electronics Packaging Research and The Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721

J. Electron. Packag 120(1), 89-97 (Mar 01, 1998) (9 pages) doi:10.1115/1.2792291 History: Received October 25, 1996; Revised October 20, 1997; Online November 06, 2007


Experiments were performed to measure the heat transfer coefficient on the surface of a square flush heat source mounted at the center of an FR-4 plate in a small horizontal enclosure. The plate area was six times larger than the heat source area. Four cases were considered: the plate facing upwards and downwards, and the backside either insulated or convecting. The heat transfer coefficients exhibited distinct behavior at high aspect ratio in which the dominant length scales were related to the source. At intermediate aspect ratios, the length scales of both the source and the enclosure were relevant, and at small aspect ratios a conduction limit was observed. The heat transfer coefficients at high aspect ratios exceeded the prior correlations by 14 percent for upward facing isolated plates when the ratio of heat source area to perimeter was used as the significant length scale, but the dependence on Ra1/4 was consistent. For the downward facing case, the data exceeded the values for a uniformly heated isolated plate by 68 percent. Classical correlations for shallow differentially heated horizontal enclosures were not satisfactory in describing the dependence on enclosure height.

Copyright © 1998 by The American Society of Mechanical Engineers
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