Flow Boiling of Water in Pin-Fin Enhanced Microgap

Abstract

This study experimentally investigated flow boiling of water in a closed flow loop system at reduced pressure with a wide range of heat fluxes, mass fluxes, and inlet fluid temperatures. Two microgaps with the same height of 200 μm, one with sparse pin fins, and the other with dense pin fins, were studied and compared. The transverse and longitudinal pitches were both 400 μm for the microgap with sparse pin fins, and were both 200 μm for the one with dense pin fins. The pins were circular with a diameter of 150 μm for both microgaps. The pin fins were arranged in a staggered way, and covered an area of 1 cm × 1 cm. New two phase heat transfer and pressure drop correlations were proposed based on the current study. Two phase flow instabilities were observed under certain conditions and were discussed. High speed visualization was utilized to characterize two phase flow patterns. Effects of spatially non-uniform surface heating on two phase flow were studied. The heat transfer and pressure drop performance of dielectric liquid HFE-7200 was tested and compared with water. Two phase heat transfer coefficient and pressure drop correlations were also developed for HFE-7200.