Effects of operation parameters on flow boiling characteristics of heat sink cooling systems with reentrant porous microchannels

• A type of Ω-shaped reentrant porous microchannels (RPM) was developed.
• Flow boiling performance of ethanol were accessed.
• Flow boiling performance of RPM was strongly dependent on operation parameters.
• Ethanol tests presented worse flow boiling performance than water.

Porous-based microchannel heat sinks offer potential and attractive solutions for efficient thermal management of high heat-flux devices. In this study, a unique type of reentrant porous microchannels (RPM) with Ω-shaped configurations was developed and tested in heat sink cooling systems. They were totally constructed by sintered copper powder, and were of a hydraulic diameter of 786 μm. Flow boiling experiments of the coolant ethanol were conducted in RPM at inlet subcooling of 10 °C and 40 °C, mass fluxes of 125, 200 and 300 kg/m2 s, and a wide range of heat fluxes. Flow boiling heat transfer, pressure drop and two-phase flow instabilities were comprehensively evaluated. The operation parameter effects, i.e., inlet subcooling, heat flux, mass flux and coolants, on the flow boiling performance of RPM were accessed. The results show that the reentrant porous microchannels trigger the onset of nucleate boiling (ONB) at small wall superheat under all the ethanol boiling cases due to the significant increase of nucleation sites. The dependence of heat transfer performance on heat flux and mass flux were linked to the transition of dominated heat transfer mechanisms. The pressure drop and flow instabilities were found to be significantly dependent on the inlet subcooling and heat flux. Furthermore, the comparison of ethanol and water boiling performance were performed. The results in this study provide critical information for operation optimization of the newly developed heat sink cooling systems with reentrant porous microchannels, and are of considerable practical relevance.