SINGLE BUBBLE DYNAMICS DURING NUCLEATE BOILING UNDER LOW GRAVITY CONDITIONS

An experimental study of growth and detachment mechanisms of a single bubble on a heated surface has been conducted during the parabola flights of the KC-135. Artificial cavities were made on the polished Silicon wafer which was electrically heated on the back side in order to control the nucleation superheat. A cavity 10 μm in diameter was etched at the center of the wafer. Degassed and distilled water was used as the test liquid. Bubble growth time, bubble size and shape from nucleation to departure were measured under subcooled and saturation conditions at system pressures varying from 14.7 to 16.6 Psia. The wall superheats were varied from 2.5 °C to 8.0 °C. Significantly larger bubble diameters and longer bubble growth periods than those at earth normal gravity were measured. Bubble diameters as large as 20 mm at departure were observed as opposed to about 3 mm at earth normal gravity. It is found that for the same wall superheat and liquid subcooling the bubble departure diameter can be approximately related to the gravity level through the relation D_d ∝ 1/√g. The effect of wall superheat and liquid subcooling on bubble departure diameter is found to be small. However, the growth periods are found to be very sensitive to liquid subcooling at a given wall superheat.