An explosive type of vapor bubble growth was observed during pool boiling experiments in microgravity using R-113, where heater surface superheats as high as 70 °C were attained at nucleation. This corresponds to approximately 65 % of the computed superheat limit of the fluid, compared to the approximate 30 % observed at earth gravity for the same system. Photographs and measurements of the vapor bubble growth provide evidence for rates of growth not accountable by conventional models. The photographs reveal that the liquid-vapor interface of the explosive bubbles become wrinkled and corrugated, leading to the conclusion that some type of instability mechanism is acting.
The classical hydrodynamic instability theories of Landau and Rayleigh-Taylor, used in conjunction with a model of the early growth of spherical vapor bubbles developed by the authors, predict that the early growth should be stable. These theories do not consider the effects of heat transfer at the interface, which is believed responsible for the observed instability of the evaporating surface. This was confirmed by the mechanisms proposed by Prosperetti and Plesset which, although including the effects of heat transfer, required that the unperturbed liquid temperature distribution be known at the moment of onset of the instability. This is generally unknown, so that no comparisons with experiments were possible up to this point. The present pool boiling experiments conducted in microgravity, some of which result in the explosive vapor bubble growth referred to, permit the precise determination of the unperturbed liquid temperature distribution using a model of the early vapor bubble growth along with the measurement of heater surface temperature at nucleation. The limited results to date provide good agreement with the mechanisms proposed by Prosperetti and Plesset.
|Explosive Bubble Growth taken under Microgravity|