Laser Interferometric Investigation of Microlayer Evaporation for Various Levels of Subcooling and Heat Flux

Abstract

<p>An experimental study of the growth and evaporation of the microlayer, underlying a bubble during nucleate boiling heat transfer to dichloromethane, is presented. The influence of heat flux (8000 Btu/hr ft² - 20,000 Btu/hr ft²) and subcooling (0ºF - 13.5ºF) upon the rates of growth and evaporation, have been studied using laser interferometry and high speed photography through the glass heater surface on which bubbles were nucleated. The results presented indicate that the microlayer thickness is of the order of 5 μm. The analysis of these results confirms that the microlayer evaporation phenomenon is a significant heat transfer mechanism representing approximately 25% of the total nucleate boiling heat transfer rate for the conditions investigated. As subcooling is increased from saturation, the contribution of the microlayer evaporation to the total heat transfer rate varies in accordance with two interacting processes in the region investigated. This variation appears as an initial decrease followed by an increase.</p>