bubbles 😄

Acoustically Enhanced Condensation

Vapor bubbles are formed by direct injection into quiescent liquid in a sealed tank under controlled ambient pressure that varies from atmospheric to partial vacuum. The bubbles are injected vertically from a pressurized steam reservoir through nozzles of varying characteristic diameters, and the actuation is applied during different stages of the bubbles formation and advection.

It is shown that kHz range acoustic actuation leads to excitation of high-amplitude surface capillary (Faraday) waves at the vapor-liquid interface that significantly increases the condensation rate. The increase in condensation rate is affected by the surface waves that increase the mixing in the thermal boundary layer surrounding the bubble, which can be confirmed using Schlieren images.

khz enhanced condensation

Ultrasonic acoustic actuation may also be used for condensation enhancement. While kHz-range acoustic actuation typically couples to capillary instability of the vapor-liquid interface, ultrasonic (MHz-range) actuation leads to the formation of a liquid spout that penetrates into the vapor bubble and significantly increases its surface area and therefore condensation rate. Focusing of the ultrasonic beam along the spout leads to ejection of small-scale droplets from that are propelled towards the vapor liquid interface and result in localized acceleration of the condensation.