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RESEARCH PAPERS: Boiling and Condensation

Orientation Effects on Critical Heat Flux From Discrete, In-Line Heat Sources in a Flow Channel

[+] Author and Article Information
C. O. Gersey, I. Mudawar

Boiling and Two-Phase Flow Laboratory, School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907

J. Heat Transfer 115(4), 973-985 (Nov 01, 1993) (13 pages) doi:10.1115/1.2911394 History: Received December 01, 1992; Revised March 01, 1993; Online May 23, 2008

Abstract

The effects of flow orientation on critical heat flux (CHF) were investigated on a series of nine in-line simulated microelectronic chips in Fluorinert FC-72. The chips were subjected to coolant in upflow, downflow, or horizontal flow with the chips on the top or bottom walls of the channel with respect to gravity. Changes in angle of orientation affected CHF for velocities below 200 cm/s, with some chips reaching CHF at heat fluxes below the pool boiling and flooding-induced CHF values. Increased subcooling was found to dampen this adverse effect of orientation slightly. Critical heat flux was overwhelmingly caused by localized dryout of the chip surface. However, during the low velocity downflow tests, low CHF values were measured because of liquid blockage by vapor counterflow and vapor stagnation in the channel. At the horizontal orientation with downward-facing chips, vapor/liquid stratification also yielded low CHF values. Previously derived correlations for water and long, continuous heaters had limited success in predicting CHF for the present discontinuous heater configuration. Because orientation has a profound effect on the hydrodynamics of two-phase flow and, consequently, on CHF for small inlet velocities, downflow angles should be avoided, or when other constraints force the usage of downflow angles, the inlet liquid velocity should be sufficiently large.

Copyright © 1993 by The American Society of Mechanical Engineers
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