FLOW FILM BOILING COLLAPSE AND SURFACE REWETTING IN NORMAL AND REDUCED GRAVITY CONDITIONS

In order to study the heat transfer characteristics of flow boiling un der reduced gravity conditions, a series of experiments have been cond ucted on flow quenching of a hot flat surface by Freon-113 aboard the KC-135 parabolic aircraft. The instantaneous heat flux and temperature on the horizontal surface were measured using a heat flux microsensor comprising of two 2-mu m thick thermopiles and one resistance tempera ture sensor. During film boiling, heat transfer from the hot surface t o the flowing liquid was found to be reduced under microgravity compar ed to normal gravity conditions due to the thickening of the Vapor lay er. Also, the wall superheat and the surface hear flux at the onset of rewetting and the maximum heat flux during quenching of the hot surfa ce were found to increase with the inlet liquid subcooling, mass flux and gravity level. The effect of microgravity was more important for l ow flow rate results and decreased al high flow rates.