Deterioration of water evaporation by impurity accumulation at the liquid-vapor interface during nucleate boiling

TL;DR

This study investigates how impurity accumulation at the liquid-vapor interface during nucleate boiling causes increased interfacial resistance to evaporation, explaining variability in previous data and highlighting impurity effects on boiling efficiency.

Contribution

It provides experimental evidence linking impurity accumulation to increased interfacial resistance, clarifying the cause of data dispersion on the accommodation coefficient.

Findings

Interfacial thermal resistance increases linearly with impurity accumulation.

Impurity buildup at the interface deteriorates evaporation efficiency.

Results explain variability in previous measurements of the accommodation coefficient.

Abstract

The interfacial resistance to evaporation, in particular for the case of water, is a longstanding issue. The previous data on its main characterizing parameter, the accommodation coefficient, manifest a dispersion over three orders of magnitude. We study the evaporation of a thin liquid layer (microlayer) under the growing single bubble in saturated pool boiling of ultra-pure water at atmospheric pressure. However, the water contamination during the experiment cannot be excluded. The local and instantaneous data on interfacial thermal resistance are recovered from the synchronous local measurements of the microlayer thickness and the heater temperature. At each particular interfacial point, the resistance shows a linear increase in time suggesting the effect of accumulation of impurities at the interface. We compute the water mass evaporated at a given point of microlayer that should be proportional to the interfacial concentration of accumulated impurities. A clear increase of the interfacial thermal resistance with the evaporated mass is observed. This demonstrates a link of the temporal increase of the interfacial resistance (i.e. the evaporation deterioration) with the accumulation of impurities at the interface, which can explain the dispersion of the published data on the accommodation coefficient.