Numerical investigations on the origin of rapid evaporation *

The unstable growth of a vapor bubble in a pool of highly superheated liquid has been a problem of long-standing interest. While the origin of the unstable growth has been suggested to be due to Landau instability, Rayleigh-Taylor (spherical) instability, and other instability mechanisms (such as vapor recoil), these speculations have not been fully vetted because of insufficient experimental or computational data. Here we use Direct Numerical Simulations to study the origin of unstable vapor bubble growth for several fluids of interest and compare the results with the theoretical predictions. To this end, we follow the evolution of an initially small vapor seed in a pool of superheated liquid. The surface of the vapor seed is perturbed slightly to trigger instability. The onset of instability is identified when the bubble surface starts to roughen. The effects of the key controlling parameters, such as liquid superheat and liquid/vapor properties on the onset of the instability are investigated. Selective experiments are also performed by University of Washington team to aid the computational modeling.