Two-Phase Particle Image Velocimetry Visualization of Rewetting Flow on the Micropillar Interfacial Surface.

Abstract

Boiling heat transfer has a high thermal efficiency by latent heat absorption, which makes it an attractive process for cooling electronic device chips. Critical heat flux (CHF), the maximum heat flux, is a crucial factor determining the operating range of the boiling applications. The CHF can be enhanced by improving the fluid supply to the boiling surface. Herein, micropillar interfacial surfaces have been proposed to increase the CHF by increasing the rewetting flow, which determines the fluid-supply capacity near the bubble contact line. A state-of-art two-phase particle image velocimetry (two-phase PIV) technique is introduced for rewetting flow measurement on micropillar structures (MPSs) to analyze the CHF-enhancement mechanism. The two-phase PIV visualization setup offers high spatial (∼120 μm) and temporal (∼2000 Hz) resolutions for measuring rewetting flow during bubble growth. The MPS samples exhibit enhanced CHF and rewetting flows compared to those on a plain surface. The roughest case, D04G10 sample, had a CHF of 164 W/cm2, 1.84 times higher than that of the plain surface. The D04G10 sample also recorded the highest rewetting velocity of 0.311 m/s, 4.7 times higher than that of the plain surface. The comparison between the rewetting flow and wicking performance shows that wicking-induced flow accounted for a substantial part (∼17%) of the rewetting flow and contributed significantly to the CHF enhancement owing to large rewetting flow by delaying vapor-film formation. Based on these findings, a new CHF model suggested by introducing the rewetting parameter shows a high CHF prediction accuracy of 94%.