Research on mechanisms of flow and heat transfer in self-rewetting fluids using molecular dynamics

Self-rewetting fluid, which acts as a proficient heat transfer medium, holds great potential in the field of droplet evaporation. However, it is hard to fully analyze the enhanced heat transfer mechanism of self-rewetting fluids at the nanoscales. In this study, the Molecular Dynamics simulation is adopted to investigate the evaporation heat transfer characteristics of n-butanol-water droplets at the nanoscale. After validating the force field, the TIP4P force field model is chosen for water molecules in the droplet system, while the OPLS-AA force field model is used for n-butanol molecules. A constant-temperature evaporation model is constructed for butanol-water droplets with different mass fractions (1.00 wt%, 3.00 wt%, 5.00 wt% and 7.00 wt%) on a copper substrate to explore the effects of evaporation heat transfer. To understand the enhanced heat transfer mechanism of nbutanol-water droplets at the nanoscale, further investigations are conducted on temperature distribution, molecular potential energy and the motion trajectory of n-butanol molecules within the droplets. The results show that the evaporation of n-butanol-water droplets at concentrations of 1.00 wt%, 3.00 wt%, 5.00 wt% and 7.00 wt % exhibited a relative increase in the number of evaporated molecules compared to water droplets on 373K copper substrate. The increments were recorded at 12.62 %, 30.66 %, 61.84 % and 98.74 %, respectively. The addition of n-butanol molecules in water droplets leads to a wider spreading range of the thin liquid film, a more flattened shape of the high-temperature region at the bottom of the droplet, and an increased area of the hightemperature region. Furthermore, low potential energy n-butanol molecules tend to distribute on the surface of the droplets and are driven by heat to move on the droplet surface, thus enhancing the disturbance on the droplet surface and reducing the energy barrier for droplet evaporation.