On temperature discontinuity at an evaporating water interface

TL;DR

This study investigates the temperature discontinuity at evaporating water interfaces, revealing that previous measurements of large discontinuities were influenced by boundary conditions and that the true interfacial temperature difference is less than 0.1 K.

Contribution

The paper demonstrates that the observed temperature discontinuities are affected by boundary conditions and provides a more accurate assessment of the true interfacial temperature difference.

Findings

Measured discontinuities are strongly affected by boundary conditions.

Actual temperature discontinuity across the interface is less than 0.1 K.

Proper vapor heat flux suppression is necessary for accurate interfacial temperature measurement.

Abstract

Evaporative mass flux is governed by interfacial state of liquid and vapor phases. For closely similar pressures and mass fluxes of liquid water into its own vapor, 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 on understanding and theoretical modeling of evaporation. Here, through study of vapor transport by Boltzmann transport equation solved through Direct Simulation Monte Carlo Method, we demonstrated that the measured discontinuities were strongly affected by boundary condition 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 these studies. To accurately capture the interfacial state, the vapor heat flux should be suppressed.