Molecular dynamics simulation of evaporation coefficient of vapor molecules during steady net evaporation in binary mixture system. (1st June 2022)

• Record Type: Journal Article
• Authors: Tabe, Hirofumi; Kobayashi, Kazumichi; Fujii, Hiroyuki; Watanabe, Masao
• Is Part Of: International journal of heat and mass transfer. Volume 188(2022)
• Publication Date: 2022-06-01
• Subjects: Evaporation coefficient -- Non-equilibrium state -- Net evaporation -- Vapor–gas binary mixture; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2022.122663
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Steady net evaporation in binary mixture system is analyzed using molecular dynamics. MD system that can analyze extreme case of non-equilibrium evaporation is proposed. Effect of gas molecules on evaporating vapor molecules is discussed. Evaporation coefficient shows same value in equilibrium and non-equilibrium states. Relation between evaporation coefficient and molecular collisions is investigated. Abstract: In this study, an evaporation coefficient representing the evaporation rate of vapor molecules was calculated in a vapor–gas binary mixture and non-equilibrium system using molecular dynamics simulation. The non-equilibrium herein refers to a state in which the net evaporation of vapor molecules occurs, and the calculation system is composed of vapor molecules and non-condensable (NC) gas molecules. The evaporation coefficient in the non-equilibrium state was demonstrated to have almost the same value as that in the equilibrium state. The number density of NC gas molecules around the gas–liquid interface, which is related to the probability that vapor molecules are prevented from evaporating owing to molecular collisions, is shown to be independent of the system state. This makes the evaporation coefficient the same regardless of whether the system is in equilibrium or non-equilibrium. In contrast, the evaporation coefficient decreased as the molar fraction of the NC gas molecules increased. The increase in the molar fraction causes a higher number density of NC gas molecules around the gas–liquid interface, leading to an increase in the number of molecular collisions, which prevents vapor molecules from evaporating. Moreover, it was clarified that the change in the interface structure caused by the presence of NC gas molecules affects the velocity distribution of evaporation vapor molecules.