Convective heat transfer from a sphere due to acoustic streaming

Abstract

Convective heat transfer from a rigid sphere due to acoustic streaming is discussed for large streaming Reynolds numbers. The work is motivated by a need for the thermal analysis of the experiments on containerless materials processing using acoustic levitation. The acoustic signals used in these experiments give rise to a strong steady fluid motion around levitated alloy samples. The associated convective heat transfer rates are significant enough to give rise to heating/cooling rates in the samples which are crucial in determining their material structure and hence their thermophysical properties. The steady heat transport effect due to the streaming motion is studied with the levitated sample modeled as an isolated solid sphere in a pure plane standing sound field. Strong acoustic signals in the range of 150–170 dB and 1–2 kHz are considered. Analytical and numerical solution techniques are used to obtain a Nusselt number correlation for the heat transfer when the surrounding fluid is a gas with Prandtl number ∼O(1). A simple experiment performed to confirm some of the predictions is found to give very good agreement with the analysis. A more detailed report of the results of this study may be found elsewhere [J. Heat Transfer 115, 332–341 (1993)]. [Work supported by NSF Grant No. CTS-8918777 and the NRC.]