Molecular dynamics simulation of interfacial heat transfer characteristics of CO2, R32 and CO2/R32 binary zeotropic mixture on a smooth substrate

INTERNATIONAL JOURNAL OF REFRIGERATION(2024)

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摘要
Mixture fluids have the advantage of a flexible adjustment of the physicochemical properties by actively tuning the composition and concentrations, showing promising potential in thermal and power-related applications. However, mixtures are mainly zeotropic with heat transfer deterioration during the boiling process, resulting in a challenge to gain a comprehensive understanding of their microscopic phase change. In this study, molecular dynamics simulations were employed to investigate the nanoscale behavior of CO2, R32 and CO2/R32 mixtures. The equilibrium molecular dynamics (MD) method and the non-equilibrium MD method was utilized to study the vapor-liquid interface characteristics and the boiling heat transfer characteristics of zeotropic mixture, respec-tively. The results revealed that the thickness of the vapor-liquid interface was linearly related to the temper-ature, and the surface tension displayed significant fluctuations in both solid-liquid and vapor-liquid interfaces, which indicated a potential barrier for molecular transport. Compared to the pure components, the inception of nucleation boiling and vapor film formation of the mixture fluid was significantly delayed. The heating and evaporation rate, heat flux of mixture were lower, while the thermal resistance was significantly higher. Moreover, the time required for bubble nucleation and the formation of vapor film decreased notably with the enhanced wetting characteristics. The findings in this study provide a molecular-scale insight into zeotropic mixture boiling heat transfer and the possible wettability regulation to improve the heat transfer performance of zeotropic mixtures and promote their wider applications.
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关键词
Zeotropic mixtures,Molecular dynamics,Boiling heat transfer,Vapor-liquid interface,Low-GWP refrigerant
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