The Influence of Gas Extraction on Bubble Dynamics

A new thermal management method for hotspots on microprocessors is under development that employs confined pool boiling with vapor extraction at pre-determined nucleation sites. Extraction is accomplished by locating a vacuum chamber constructed out of a glass tube and a hydrophobic membrane directly above a nucleation site. In order to elucidate the underlying physics of vapor extraction, an adiabatic experiment was conducted to isolate the hydrodynamics. Air was injected at a rate of 90 mm³/s through an orifice of diameter 0.5 mm submerged in water at ambient temperature to generate isolated gas bubbles. The effect of varying the gap height between the orifice and the extraction surface was studied over a range from 1.22 mm to 3.49 mm. Bubble departure diameters were observed to be 80% of the gap height, and bubble departure frequencies were observed to be inversely related to departure diameter. Correlations for departure diameter, rupture diameter, and departure frequency were developed. The foundations of a theoretical static force balance to determine confined departure diameters was developed along with a theoretically based transient bubble diameter model to predict bubble departure frequency. A detailed design of the adiabatic test device is also included