Enhanced Two-Phase Heat Transfer by Direct-Contact Condensation Using Directional Acoustic Actuation

While two-phase heat transfer using direct-contact condensation in a liquid pool can accommodate the heat fluxes associated with cooling high-powered electronic hardware, its coupling to system-level heat transfer may be hampered by marginally-subcooled liquid and slow conductive heat transport at the liquid-vapor interface. The condensation and thereby the performance of thermal management systems that utilize two-phase heat transfer can be significantly enhanced by deliberate intensification of the condensation that is effected using nonintrusive, low-power acoustic actuation that exploits the interfacial acoustic impedance mismatch at the liquid-vapor interface. The present investigations focus on the mechanisms of acoustic enhancement in two-phase heat transfer at actuation wavelengths of O(1 mm). It is shown that the actuation enhances direct contact condensation by bulk deformations at vapor-liquid interface and injection of subcooled liquid into the vapor volume. This effect is harnessed at several actuator orientations relative to the vapor flow and actuation duty cycles, demonstrating the robustness of the heat transfer enhancement.