Boiling heat transfer of CO2/lubricant on structured surfaces using molecular dynamics simulations

In this paper, the molecular dynamics (MD) simulations are employed to investigate the effects of lubricant (PEC4) on the boiling heat transfer of CO2 on the structured surface. The results show that the structured surfaces can enhance the nucleation boiling of CO2 by providing effective bubble nucleation sites and larger heat transfer areas. However, with the increase of the mass fraction of PEC4, the nucleation boiling heat transfer efficiency decreases on the structured surface. The distribution characteristics of the CO2/PEC4 mixture during the boiling process show that parts of CO2 molecules in the liquid mixture are more likely to be adsorbed by the double-bonded oxygen atoms and carbon atoms of the ester groups of the PEC4 molecules, which hinders the movement and phase transition process of CO2 molecules. Therefore, the PEC4 molecules in the nucleation region first migrate to the top liquid region before bubble nucleation, and then bubble nuclei comes into being. When the mass fraction of PEC4 is higher than 7 wt%, the nucleation temperature is increased by 10 K to 20 K. The decrease of the CO2 nucleation boiling heat transfer performance caused by PEC4 is the consequence of the coaction of many factors, including that the lubricant leads to a decrease in self-diffusion coefficient of CO2, an increase in liquid phase viscosity, an increase in bubble nucleation temperature of CO2, and a decrease in heat transfer resistance of the solid-liquid interface.