Pool Boiling Curve in Microgravity

Abstract

Pool boiling experiments using R-113 were conducted in the microgravity of space on a flat heater, consisting of a semitransparent gold film sputtered on quartz substrate, 19.05 x 38.1 mm (0.75 x 1.50 in.). Transient measurements of both the mean heater surface temperature and input heat flux are used to compute the mean heat transfer coefficient at the heater wall. Steady-state pool boiling is achieved in microgravity under conditions in which a large vapor bubble somewhat removed from the heater surface is formed, which acts as a reservoir for the nucleating bubbles. The steady nucleate boiling heat transfer is enhanced materially in microgravity relative to that in Earth gravity, whereas the heat flux at which dryout occurs is considerably less. Using quasisteady data obtained during periods in which some significant portions of the heater surface were dried out, it was possible to construct two distinct composite approximate microgravity pool boiling curves for R-113, one for the higher level of subcooling and one for the lower level of subcooling. These are compared with a reference curve for pool boiling at a/g = +1, constructed from available data and correlations deemed to reasonably represent the circumstances present.