On the transition between contact line evaporation and microlayer evaporation during the dewetting of a superheated wall

Abstract

We present experimental results on the transition between contact line evaporation and microlayer evaporation during the dewetting of a superheated wall. The length and thickness of the liquid microlayer is measured, both showing a dependency on the wall superheat, dewetting velocity, and heating power.This work falls within the continuing efforts of understanding the formation of the so called microlayer: a thin liquid film, that is observed for example during boiling underneath a growing vapor bubble. The short lived and small scale nature of the phenomenon make accurate measurements difficult, therefore a novel experimental set-up is proposed that allows high resolution measurements in a steady-state manner. The time resolved formation of the microlayer is described in detail and the influence of the dewetting velocity, wall superheat, and heating power is discussed. Microlayer formation is observed only if a critical velocity is exceeded for a given combination of wall superheat and heating power. Below this threshold velocity, contact line evaporation dominates the heat transfer. The dependency of the microlayer length and thickness on the dewetting velocity is described using power laws. Instability effects near the contact line are observed at high dewetting velocities and high wall superheat. It is concluded that microlayer evaporation and contact line evaporation exist in separate regimes, obviously separated by a parameter combination of dewetting velocity, wall superheat, and heating power.