Exploring the inequality of evaporation and condensation coefficients based on ISS experiments

Phase change is a complex problem, and kinetic theory has been used to model it for over a decade. However, due to unknown values of evaporation and condensation coefficients, the applicability of the kinetic theory is still limited. These coefficients are necessary inputs and denote the fraction of molecules that undergo phase change. For the sake of simplicity and closure, the evaporation and condensation coefficients are often assumed to be equal (and often called an "accommodation" coefficient), The current study aims to investigate this assumption, using the Constrained Vapor Bubble (CVB) experiment data from the ISS. Interferometric image analysis of the CVB data enables a complete reconstruction of the liquid-vapor interface. Thermal transport is modeled using the temperature profiles obtained from the CVB dataset. A multi-scale phase change model is developed to calculate the local phase change flux at all points across the 3D interface using a unique "active surface" meshing technique. The model accounts for the interfacial curvature, disjoining pressure, and thermo-capillary effects in the contact line region. The CVB cell being a closed system allows for an additional governing equation: the surface-integral of the phase change flux over the entire interface is zero. The additional equation enables the decoupling of the evaporation and condensation coefficients and indicates a potential inequality.