Heat Flow and Sonic Microstreaming

Abstract

Measurements are being made to determine solid-to-liquid heat flow in the presence of sonically induced microstreaming near the interface. The microstreaming is induced by an air bubble vibrating near the region of heat flow. The air bubble is placed by means of a micropipette on the bottom of a clear plastic chamber containing the liquid. A 2-kc piston vibrator operated at low amplitudes a few centimeters above the bubble causes the bubble to become a strong source of sonic microstreaming. Imbedded in the plastic on which the bubble sits, and concentric with the bubble, is a thin multilayered annulus, the top of which is flush with the surface of the plastic. For a typical annulus the too layer is copper foil, the second is constantan; the bottom layer is a thermistor wafer through which current can be sent to produce a desired amount of heating. The thermal emf developed at the copper-constantan junction can be measured. Thus we have a source of known heat flow and known surface temperature. Investigations have been carried out in which heat flow was measured as a function of sonic amplitude, the surface temperature of the annulus being kept constant. The results indicate that, when the sonic amplitude A is small, the heat flow H varies linearly with A. This linear relationship between H and A is in agreement with the predictions of a simplified theory. At higher amplitudes the bubble may move about erratically, so that consistent readings are difficult to obtain. (Supported in part by the U. S. Air Force Office of Scientific Research.)