Role of easy-to-activate nucleation sites in pool boiling
Journal
International Heat Transfer Conference
Journal Volume
2018-August
Pages
653-660
Date Issued
2018
Author(s)
Abstract
Nucleate boiling from heated surfaces is an efficient heat transfer approach by taking advantage of the large latent heat of vaporization of liquids. Despite decades of research, the mechanism triggering the critical heat flux is still unclear because of the difficulty posted by the random flow nature at high heat fluxes. In this work, we show that the effectiveness of nucleation sites, usually characterized at low heat fluxes, significantly affects the heat transfer coefficient and the critical heat flux in pool boiling. Boiling experiments were conducted on a total of four types of microstructured surfaces with controlled effectiveness of nucleation sites and surface wettability. It is shown that surfaces with easy-to-activate nucleation sites have much higher heat transfer coefficients than those surfaces with ineffective nucleation sites. More importantly, our study reveals that excellent critical heat flux (up to 219.4 W/cm2) is attainable only when the surface has good wetting property but is free of easy-to-activate nucleation sites. With the presence of easy-to-activate nucleation sites, only limited critical heat fluxes can be achieved irrespective of the surface wettability, suggesting a suppression effect of nucleation sites on the critical heat flux. A wetting-deterioration mechanism is proposed to explain the suppression effect of easy-to-activate nucleation sites on the critical heat flux. Easy-to-activate nucleation sites continuously generate bubbles that block the liquid to cool down the hot surface and thus lead to early dry-out. ? 2018 International Heat Transfer Conference. All rights reserved.
Subjects
Critical heat flux
Easy-to-activate nucleation sites
Heat transfer coefficient
Microstructured surfaces
Pool boiling
Type
conference paper