Dielectrophoresis with application to boiling heat transfer in microgravity. II. Experimental investigation

The objective of this paper is to analyze experimentally the feasibility of utilizing the dielectrophoretic (DEP) force to sustain boiling in space wh ere the gravity-driven buoyancy force is absent. First, a bubble trajectory experiment is present to determine the magnitude of the DEP force produced at the edge of two diverging-plate electrodes to the highly nonuniform ele ctric field. The results showed that the DEP forces measured experimentally are equal to those predicted in Part I to within 10%-15%. Second, the bubb le detachment diameter and frequency of bubbles generated with a gold-film, single-bubble heater were measured in microgravity so that the masking eff ect of gravity could be eliminated. In particular, a comparison is made bet ween the DEP forces produced with a relatively high-electric-field gradient at the edge of two flat-plate electrodes to the DEP forces produced with t he relatively low electric-field gradient between two diverging-plate elect rodes. It was discovered that the bubble detachment diameter and frequency could be reduced to a single curve by plotting the data against effective g ravity ratio [g((b,e))] due to the dielectrophoretic forces. In this way, t he normalized bubble diameter at the time of breakoff from the heated surfa ce was found to vary inversely as the effective gravity ratio to the 1/2 po wer. (C) 2001 American Institute of Physics.