Numerical simulation of flash evaporation in the presence of secondary nucleation

Abstract

Rapid depressurization of a stagnant liquid below its prevailing saturation brings it to a metastable superheated state. Thermodynamic equilibrium is regained through a rapid evaporation or flashing which starts in a thin layer at the free surface and continues to propagate downward by nucleation and evaporation in the subsequent layers of superheated liquid below it. Secondary nucleation (from spurious locations) in the bulk of the superheated liquid or from the wall of the container uniquely affects the propagation of the free surface evaporating front.We computationally simulate the propagation of evaporating front in the presence of secondary nucleations, adopting a one dimensional, compressible two-phase flow model with diffuse interface. For simulating secondary nucleation at pre-determined sites, vapour density is assumed at the location and active interface is imposed locally.Secondary nucleation is noted to slow down the propagation of the evaporating front while the effect is more prominent with the proximity of the site. The secondary phase change interface is observed to grow towards the primary one and has a higher velocity as has been reported in different experiments. Secondary nucleation also hinders the propagation of the wave reflected back from the end of the domain. We also discuss some limitations of the model.