Temperature Discontinuity at an Evaporating Water Interface

Evaporative mass flux is governed by the interfacial state of liquid and vapor phases. For closely similar pressures and mass fluxes of liquid water into its own vapor, the discontinuity between interfacial liquid and vapor temperatures in the range of 0.14-28 K is reported. This controversial discontinuity has resulted in an obstacle to understanding and theoretical modeling of evaporation. Here, through the study of vapor transport by the Boltzmann transport equation solved through the direct simulation Monte Carlo Method, we demonstrated that the measured discontinuities were strongly affected by boundary conditions on the vapor side of the interface and do not reflect the interfacial state. The temperature discontinuity across the evaporating interface is <= 0.1 K for all of these studies. To accurately capture the interfacial state, the vapor heat flux should be suppressed.