Molecular Dynamics Study On Microscopic Characteristics Of Water Vapor Condensation

The condensation of water vapor has a wide range of applications and important functions in many fields,such as refrigeration,heating,power generation,enhanced heat transfer and removal of fine particles.The condensation of water vapor can be divided into homogeneous condensation and heterogeneous condensation according to the nucleation mechanism.The condensation process is a physical phenomenon involving microscopic to macroscopic phenomena.At present,people’s understanding of microscopic mechanisms is not yet comprehensive.From the microscopic point of view,this paper uses molecular dynamics simulation(MD)to study the condensation characteristics of water vapor.Supersaturation and temperature are two important parameters affecting the phase transition of water vapor condensation.In this paper,the method of MD is used to simulate the condensation of water vapor under different supersaturation and temperature,and the simulation results are compared with the calculated results by traditional nucleation theory(CNT).Analysis of the condensation of water vapor at different degrees of supersaturation shows that,in the homogeneous condensation of water vapor,the homogeneous nucleation rate increases with the increase of supersaturation,but the MD simulation value of homogeneous nucleation rate is lower than the classical nucleation theory.In the heterogeneous condensation of water vapor,the MD simulation results of the heterogeneous growth rate will be higher than the classical nucleation theory calculations.The heterogeneous growth rate decreases as the specific surface area of the added particles decreases,particle size increases and the mass of the constituent particles decreases.Moreover,the rate difference of heterogeneous growth caused by different particles will gradually decrease with the increase of supersaturation.Secondly,the analysis of the condensation of water vapor at different temperatures shows that,in the homogeneous condensation of water vapor,the homogenization nucleation rate increases with the increase of temperature,but its value is lower than the theoretical result of CNT,and the higher the temperature,the greater the difference.In the heterogeneous condensation of water vapor,the MD simulation value of the heterogeneous growth rate is higher than the classicalnucleation theory calculation,and this difference will increase with the increase of temperature.The difference of heterogeneous growth rate caused by different particle size and shape will increase with the increase of temperature,but the difference caused by different particle composition will decrease with the increase of temperature.