Enhanced boiling heat transfer on micromachined surfaces using acoustic actuation

Two-phase thermal management based on submerged boiling heat transfer has received considerable attention in recent years because of its potential to enable high heat flux using relatively simple hardware and system-level coupling. However, the utility of this attractive heat transfer approach has been hampered by the critical heat flux (CHF) limit on the maximum heat transfer owing to the dynamics of the vapor bubbles that form on the heated surface and the transition to film boiling that results in a large increase in surface temperature. Recent work at Georgia Tech has exploited low-power ultrasonic acoustic forcing to enhance boiling heat transfer and increase the CHF limit by controlling the formation and evolution of the vapor bubbles and inhibiting the instabilities that lead to film boiling. These effects are investigated over both plain and textured (surface-embedded microchannels) boiling heat transfer base surfaces (the transfer of makeup fluid to the boiling sites in the presence of surface microchannels passively decreases surface superheat and increases the CHF). Acoustic actuation has a profound effect on the boiling, and leads to a significant increase in the CHF by limiting the formation of large vapor columns and their collapse into a vapor film. Improvements in the CHF in stagnant bulk fluid exceed 65% for the plain surface (up to 183 W/cm2), and 30% for the textured surface (up to 460 W/cm2 with 7°C r eduction in surface superheat).