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

Abstract

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 levels, and mass fluxes are considered in this type of heat sink for use in applications with high fluxes up to 300 W/cm2. The design of the heat sink provides an inward radial swirl flow between parallel, coaxial disks that form a microchannel of 300 μm and 1 cm radius with a single inlet and a single outlet. The channel is heated on one side through a copper conducting surface, while the opposite side is essentially adiabatic to simulate a heat sink scenario for electronics cooling. Flow boiling heat transfer and pressure drop data were obtained for this heat sink device using water at near atmospheric pressure as the working fluid for inlet subcooling levels from 20 to 81°C and mean mass flux levels ranging from 184 to 716 kg/m2s. To explore the effects of varying surface wetting, experiments were conducted with two different heated surfaces. One was a clean, machined copper surface with water equilibrium contact angles in the range of 14–40°, typical of common metal surfaces. The other was a surface coated with zinc oxide nanostructures that are superhydrophilic with equilibrium contact angles measured below 10°. During boiling, increased wettability 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. Reducing inlet subcooling levels was also found to reduce the magnitude of oscillations in the oscillatory boiling regime. The highest heat transfer coefficients were seen in fully developed boiling with low subcooling levels as a result of heat transfer being dominated by nucleate boiling. The highest heat fluxes achieved were during partial subcooled flow boiling at 300 W/cm2 with an average surface temperature of 134 °C and requiring a pumping power to heat rate ratio of 0.01%. The hydrophilic surface retained wettability after a series of boiling tests. Recommendations for use of this heat sink design in high flux applications is also discussed.

Water Wicking and Droplet Spreading on Randomly Structured Thin Nanoporous Layers

“…The superhydrophilic nature of these surfaces make hemispreading 6,28 (in which the contact line of the upper droplet separates from the leading edge of liquid, spreading out into the porous nanostructure) possible. The nanostructure surface features listed above are of central interest here because they were characteristics observed experimentally for superhydrophilic ZnO nanostructured surfaces studied by Ruiz et al 30 and Padilla and Carey, 23 and they are expected to be representative of the behavior for other similar superhydrophilic nanostructured surfaces. Previous studies of droplet spread on surfaces mentioned above have not considered this specific type of surface.…”

A Review on Microchannel Fabrication Methods and Applications in Large-Scale and Prospective Industries

“…Additionally, a number of researchers have created and put to the test microchannels in theoretical 404) and numerical 331) investigations. They have established that microchannels, including radial arrays 405) , straight, rectangular 406) microchannels, and pin finned microchannels 407) , perform better when it comes to dispersing a significant amount of heat 408) . The outcomes of trials conducted under comparable conditions were then contrasted with those predicted by theory.…”