Abstract

Advanced power electronic devices are capable of handling exceptional power densities, which result in requirements to dissipate large localized heat fluxes.  Hot spots exceeding 1kW/cm2 pose a severe cooling challenge.  The high heat transfer coefficients possible with capillary fed, two phase cooling are attractive for addressing highly non-uniform heat flux distributions and have been applied extensively in systems such as heat pipes and vapor chambers.  The performance of these systems often depends strongly on large scale mass and energy transport as well as microscale processes.  Patterning of porous material and control of porosity down to the nanoscale have been shown to enhance both heat transfer coefficients as well as maximum allowable heat fluxes.
Here we apply electrodeposition around a sacrificial template with tailored microstructure, which has previously been shown to produce porous materials with favorable thermal and fluidic properties, to produce small scale (e.g. 0.3 mm) capillary fed, two-phase cooling structures.  Joule heating of the structures allows highly localized application of heat, and we have characterized their cooling performance over a broad range of heat fluxes.  Using water as a working fluid at ambient pressure, the structures are capable of dissipating more than 1200 W/cm2 with temperature changing less than 5 K over ranges in heat flux spanning more than 800 W/cm2 and with absolute superheats of less than 10 K.  We characterize the variation of device performance on both the bulk geometry of the porous material and its microscale structure and compare with existing porous structures and plain surfaces. We modify models of boiling in capillary fed porous structures to predict device performance.