Boiling Heat Transfer Performance in a Spiraling Radial Inflow Microchannel Cold Plate

This study presents an experimental exploration of flow boiling heat transfer in a spiraling radial inflow microchannel heat sink. The effect of surface wettability, fluid subcooling, and mass fluxes are considered. The design of the heat sink provides an inward radial swirl flow between parallel, coaxial disks that form a microchannel of 300 microns. The channel is heated on one side, while the opposite side is essentially adiabatic to simulate a heat sink scenario for electronics cooling. To explore the effects of varying surface wetting, experiments were conducted with two different heated surfaces. One was a clean, machined copper surface and the other was a surface coated with zinc oxide nanostructures that are superhydrophilic. During boiling, increasedwettability resulted in quicker rewetting and smaller bubble departure diameter, as indicated by reduced temperature oscillations during boiling, and achieving higher maximum heat flux without dryout. The highest heat transfer coefficients were seen in fully developed boilingwith low subcooling levels as a result of heat transfer being dominated by nucleate boiling. The highest heat fluxes achieved were during partial sub cooled flowboiling at 300 W/ cm(2) with an average surface temperature of 134 degrees Celsius. Recommendations for electronics cooling applications are also discussed.