Molecular dynamics simulations of nanodroplet evaporation of refrigerants

Abstract

Abstract As the working fluid of energy transfer and conversion, refrigerants are essential in refrigeration and power systems. In order to improve the efficiency in power system, and reduce the design cost of evaporator, it is important to reveal the evaporation mechanism of refrigerants. In this study, the evaporation of R600 (butane), R134a (1,1,1,2-tetrafluoroethane), R32 (difluoromethane), and R1234yf (2,3,3,3-tetrafluoro-1-propene) was studied using molecular dynamics simulations. The internal fields such as density, radial mass fluxes of the molecular systems during the evaporation are compared. Besides, the prediction accuracy of the traditional diffusion-based model was evaluated. The results show that the prediction accuracy of traditional diffusion-based model is low due to the vapor thermal conductivity affected by the scale effect. A modified model based on vapor thermal conductivity with rarefied gas effect and interfacial influence is proposed to significantly improve the calculation accuracy for nanodroplet evaporation of different refrigerants. The evaporation rates of different refrigerants are affected by the molecular number density and molecular diffusion in the vapor phase near the interfacial region. The larger the molecular number density and the molecular self-diffusion coefficient are, the faster the droplet evaporation rate is.