Flow boiling in microchannel heat sinks has been studied extensively in the past decade with the aim of implementation in the cooling of high-power integrated circuit chips. It has the potential to provide high-heat flux cooling at low wall superheats and a compact heater surface geometry. Prior works using water as the working fluid have shown that open microchannels with tapered manifolds deliver enhanced flow boiling performance, with substantial improvements in flow stability and a low pressure drop. The present work investigates the use of ethanol in flow boiling via a gravity-driven flow loop, eliminating the need for a pump. The flow boiling performance, critical heat flux (CHF) behavior, and pressure drop characteristics of ethanol in open microchannels with tapered gap manifolds (OMM) are studied. Several microchannel chips with different manifold gap heights and channel geometries are tested at multiple flow rates. The performance of ethanol in the present work was found to exceed all previously published results with ethanol, with a record maximum heat flux of 217 W/cm2 at a wall superheat of 34°C. Thanks to a remarkably low pressure drop, with maximal values below 9 kPa, ethanol is identified as a suitable dielectric fluid for reaching high heat flux goals in a gravity-driven configuration investigated in this study.

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