Molecular dynamic study of evaporation in nanoslit: Influence of slit geometry and wettability

A liquid-vapor phase change is an efficient process to transfer thermal energy and has been utilized in much industrial application. To enhance the liquid-vapor phase-change heat transfer, nanoengineered materials, such as nanostructured surface, have been experimentally and numerically investigated so far. Nevertheless, understating how and how much the nanostructured surfaces influence evaporation has not been sufficient. In the present study, we employed the nanoslit systems, inside which fluid molecules initially stayed, and by means of classical molecular dynamics simulations, numerically investigated how the fluid molecules evaporated from the nanoslits, depending on the geometry and the surface wettability of the nanoslits. In the presence of the solid surface in contact with the liquid phase of the fluid, the molecular behaviors changed, especially in the vicinity of the solid wall. Some of the fluid molecules frequently collided with the gas-liquid interface at multiple times. We distinguished the molecular behavior from the reflection, and newly defined it as the retention. In the present study, it was found that, as the solid sidewall became more hydrophilic, the mobility of the molecules on the sidewall surface became higher, increasing the amount of the evaporation molecules traveling along the sidewalls. It was because the intermolecular potential was low in the vicinity of the solid walls. When the wettability of the sidewalls differed, the fluid molecules were attracted to the more hydrophilic sidewall. It caused that the gas-liquid interface got closer to the slit boundary. If the distance between the gas-liquid interface and the slit boundary was relatively short, the amount of the retention near the gas-liquid interface decreased.