Effect of thin film truncation thickness on the heat transfer underestimation from an evaporating droplet on a partial wetting surface

Abstract

The thin liquid film near the contact line is important for droplet evaporation on a heated surface, however, it remains a challenge for modeling and simulation since it operates from macroscale down to nanoscale. The nanoscale thin film profile has long been unknown; besides in CFD simulations the meshing work for the thin film could be extremely consuming therefore a truncation is needed to disregard the very thin part of the thin film region. The present study is an attempt to simplify the thin film modeling for partially wetting liquids, based on a recent Atomic Force microscope (AFM) experiments that suggested the partially wetting nanoscale thin film are closely following the macroscale profiles. We conduct a theoretical study on an evaporating sessile droplet and evaluate the effect of thin film truncation size on the overall heat transfer. A small spherical droplet with less than 1mm diameter is investigated and the wall superheat is 1 C°. The contact angles are ranged from 5o to 85o. We evaluate the effect of the dimensionless truncation ratio, i.e. the ratio of the truncation size and droplet height on the overall heat transfer underestimation. The results show that the dimensionless truncation ratio has a critical effect on the heat transfer calculation while the contact angle and the droplet size have relatively weaker influences. It is due to the fact that the variation of truncation ratio has much more effect on the size of the neglecting thin film region.