Acoustically enhanced boiling heat transfer

An acoustic field generated by a light-weight, low-power acoustic driver is shown to increase the critical heat flux during pool boiling by about 17%. It does this by facilitating the removal of vapor bubbles from the heated surface and suppressing the instability that leads to the transition to film boiling at the critical heat flux. Bubble removal is enhanced because the acoustic field induces capillary waves on the surface of a vapor bubble that interact with the bubble contact line on the heated surface causing the contact line to contract and detach the bubble from the surface. The acoustic field also produces a radiation pressure that helps to facilitate the bubble detachment process and also suppresses the transition to film boiling. The mechanisms associated with these interactions are explored using three different experimental setups with acoustic forcing: an air bubble on the underside of a horizontal surface, a single vapor bubble on the top side of a horizontal heated surface, and pool boiling from a horizontal heated surface. Measurements of the capillary waves induced on the bubbles, bubble motion, and heat transfer from the heated surface were performed to isolate and identify the dominant forces involved in these acoustically forced motions. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4721669]