Altering Bubble Dynamics via In Situ Vapor Extraction

Abstract

Spatio-temporal cooling of electronics using latent energy might be achieved by closely spaced, rapid departure of small bubbles. One means to achieve small diameters during boiling is to provide an additional upward force during bubble formation, such as that from vapor extraction. Experiments were conducted of bubble extraction using constant flow rates of both air and vapor that ranged from 30 to 90 cubic mm per second. Extraction was achieved with a hydrophobic porous membrane sealed to a tube in which a vacuum was drawn. The gap between the extraction and supply surface was varied from 0.5 to 3.25 mm. Only individual bubbles that ruptured at the top surface while still attached to the supply surface were considered. Bubble departure diameters are approximately 80 percent of the gap height. As with unconfined bubbles in pool boiling, the bubble frequency varies inversely with departure diameter. Correlations for bubble rupture, bubble departure and bubble frequency are presented as a function of gap height. Using the three distinct regimes identified in the experimental study, i.e., growth only, growth with extraction, and extraction only, an effective bubble diameter model and an appropriate static force balance were developed. These were used to predict bubble departure frequencies and diameters, respectively, under confined extraction conditions.