Flow Boiling Instabilities in Expanding Microgap Channel

Abstract

In Chap. 2, the flow boiling heat transfer and pressure characteristics of three different expanding microgap heat sinks have been reported. This present chapter aims to understand the parametric effects including heat flux, mass flux, and channel dimension on flow boiling instabilities in expanding microgap visually and experimentally. High-speed flow visualizations from the top of the microgap heat sink are conducted simultaneously along with the experiments. The different flow patterns are presented and discussed to illustrate the bubble characteristics in the flow boiling in expanding microgap heat sinks. The measured flow boiling instability data are presented in this section for three different microgap configurations: straight microgap of depth 200 μm and two expanding microgaps having the same inlet depth 200 μm with gradually increasing exit depth 300 μm and 460 μm. Results are presented for wide range of heat and mass fluxes. Results show that two-phase expanding microgap heat sink has novel potential to mitigate the flow instabilities and flow reversal issues as the generated vapor has room to expand downstream and also due to reducing shear force along the direction of expansion of the test section. Key details of the experimental setup, procedure, test section, and experimental conditions are described in Chap. 2.