Numerical Study of Growth of a Vapor Bubble in Superheated Seawater with Time-Varying Pressure

Abstract

Flash evaporation is used in a wide range of applications from seawater desalination to nuclear and space applications. The fundamental mechanism in flash evaporation is mechanical and thermal non-equilibrium which results in liquid being superheated and subsequent bubble growth. Therefore, study of bubble growth is essential to accurately predict the vapor generation rate during flashing. Accordingly, this article provides a comprehensive numerical study of growth of a single vapor bubble during flash evaporation in seawater. Effects of system pressure, liquid superheat, salt concentration, and time-varying pressure during flash evaporation on bubble growth behavior are studied. The Rayleigh-Plesset equation with energy and salt concentration equations is solved numerically with 4th-order discretization schemes. Excellent agreement between the results of the present study and reported experimental results is found. It is observed that during bubble growth in seawater, salt continuously accumulates at the vapor-liquid interface which consequently reduces the growth rate and degrades thermal performance characterized by Nusselt number. However, it elongates the inertia-controlled regime during which the bubble radius is directly proportional to time. It is shown that properly handling the non-uniform distribution of solute in the liquid boundary layer is key to modeling bubble growth in seawater and binary solutions.