Parametric Study on Flow Boiling Characteristics in <inline-formula> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula>-Shaped Re-Entrant Porous Microchannels With Structured Surface

Abstract

This paper focuses on flow boiling performance of a type of $\Omega $ -shaped re-entrant porous microchannels for efficient thermal management of high heat-flux devices. The porous-based microchannels are totally constructed by sintered irregular shaped copper powders that featured microchannel walls with structured surface. Flow boiling experiments are conducted utilizing two coolants (deionized water and ethanol) at inlet subcoolings of 10 °C and 40 °C, mass fluxes of 125–300 kg $/\mathrm {m} ^{2}\,\cdot \, \mathrm {s}$ , and a wide range of heat fluxes. Flow boiling heat transfer, pressure drop, and two-phase flow instabilities are comprehensively evaluated to access the parametric effects, i.e., heat flux, mass flux, inlet subcooling, and coolants, on the flow boiling performance of re-entrant porous microchannels with structured surface (RPM-SS). It is found that for both water and ethanol, the two-phase heat transfer coefficients of RPM-SS generally decreased, while the pressure drop increased with the increase in heat flux and vapor quality. Though severe pressure drop instabilities with large magnitude of flow oscillations occurred for RPM-SS in the ethanol tests at large inlet subcooling cases, the RPM-SS can sustain fairly stable boiling at small inlet subcooling tests without the installation of inlet restrictors.