BOILING HEAT-TRANSFER IN THE QUENCHING OF A HOT TUBE UNDER MICROGRAVITY

Quenching of a hot tube by injection of a subcooled liquid was investi gated under microgravity conditions, Liquid Freon (R-113) was injected at mass fluxes between 160-850 kg/m(2)s into an initially hot, thin-w alled stainless steel tube, 11.3 mm i.d, and 914 mm long, Data collect ed in microgravity aboard NASA's KC-135 aircraft were compared with qu enching tests in a horizontal tube under normal gravity, The rewetting temperatures were found to be 15 degrees-25 degrees C lower in microg ravity than those obtained under 1 g, and the film boiling heat transf er coefficients in microgravity were only 20-50% of the values obtaine d in 1 g, This resulted in much longer precursory cooling periods in m icrogravity, and hence, the time to totally queuch the initially hot t ube in microgravity was greatly extended, However, once the tube was c ooled sufficiently to allow axial propagation of the quench front, the rewetting velocity was found to be slightly greater in microgravity, The boiling curves shelved that the nucleate and transition boiling cu rves in microgravity were shifted to lower wall superheats as compared to 1 g as a result of the lower rewetting temperature, The heat flux profiles were otherwise quite similar, indicating that these boiling r egimes are little affected by reduction in gravity.