Predicting evaporation/condensation mass fluxes using a chemical kinetics framework: Pseudo-chemical potential as the activation energy

A new model for evaporation/condensation is developed using a chemical kinetics framework. The unidirectional evaporation/condensation flux is calculated by the Arrhenius equation, in which the activation energy is assumed to be the pseudo-chemical potential (PCP) barrier and the pre-factor is determined by the collision frequency of liquid/vapor atoms. The value of the PCP barrier is obtained from the equilibrium molecular dynamics (MD) simulations of a liquid-vapor coexisting argon system using umbrella sampling. Simulation results show that the PCP barrier from vapor to liquid is zero, and that from liquid to vapor is the PCP difference between the two phases. The collision frequency can be derived from the Maxwell-Boltzmann velocity distribution, which is established in vapor and liquid phases. A density expression of the model is further derived by estimating the PCP barrier with the densities of the liquid and vapor. The condensation fluxes calculated from the original and density expressions are consistent with the results from the MD simulations of argon condensation. Moreover, the density expression of the new model has been validated by comparing it with results from previous MD simulations for verification purposes.(c) 2023 Elsevier Ltd. All rights reserved.

Automated summary

A new model for evaporation/condensation is developed based on chemical kinetics. The model is validated through molecular dynamics simulations of argon condensation. The density expression of the model is consistent with the MD simulation results.