Studying on water nanojet ejection and the wetting phenomena on the nozzle surface

Abstract

In this research, molecular dynamics simulations of water nanojet ejection out of nozzle holes with various sizes under various pressing forces are performed. The water molecules are ejected out the nozzle by a back plate on which a constant force is applied. The results of MD simulations of water ejection show that after one ejection, about 1.3–2.5% of total molecules accumulate on the nozzle plate surface. These molecules affect the ejection of water jet thereafter. The cause of the accumulation of wetting water is investigated by analyzing the trajectories of these molecules. It is found that in the firing chamber near the nozzle plate wall, the arrangement of water molecules is aligned by the surface topology of the metal wall. Water molecules are packed into filamentous structure and these lines stack up at equal distances to each other. Water molecules drift along these lines, the trajectories of these molecules are sinuous, the velocity directions of them are random; molecules drift along the parallel lines until they reach a region of low pressure beneath the nozzle opening. These molecules eject out through the edge of the nozzle, they fall back on to the nozzle surface and eventually deposit on the nozzle surface due to low ejection velocity.