Boiling crisis controlled by capillary pumping and viscous friction: Liquid penetration length and dry spot diameter

Abstract

A boiling crisis, or critical heat flux (CHF), is a condition that determines the upper bound on removable thermal energy at a boiling surface. In such situations, the liquid cannot wet the surface because a vapor film completely covers it. CHF is enhanced on micro-structured surfaces when under boiling conditions. CHF values were measured for surfaces with rectangular microchannel geometries of various channel widths, (10-30 mu m) and generally increased in value as channel widths decreased. However, the CHF value for the 5-mu m channel-width surface was found to be lower than the wider channel-width surfaces. This observation contradicts models based on vapor recoil and classical instability mechanisms. Hence, we present a fluid-dynamics model that considers capillary pumping and viscous friction. With a focus on the spatial distribution of the liquid penetration region and the local dry spot under a large vapor bubble, this model can accurately predict the CHF variation associated with different channel widths. Published by AIP Publishing.