The influence of sound on heat transfer from a cylinder in crossflow

Abstract

This paper reports the results of an experimental investigation of the influence of intense acoustic vibrations on the rate of heat transfer from a circular cylinder ( 3 4 inch diameter) to air in crossflow. The direction of vibration was normal both to the axis of the cylinder and to the crossflow. Plane stationary sound waves were employed and the cylinder was positioned so that its longitudinal axis coincided with displacement antinodes of the sound waves; the sound frequencies used were 1100 cps and 1500cps. The results show that intense sound causes the overall convective heat-transfer coefficient to increase appreciably (up to 25 per cent) in two regions. In one of these regions, which corresponds to the lowest values of the crossflow Reynolds number employed in the experiments [( Re) cf ~ 1000], the increase in the rate of heat transfer appears to be the result of an interaction similar to thermoacoustic streaming. In the second region, which corresponds to the highest values of the crossflow Reynolds number employed in the experiments [( Re) cf ~ 10 000], the increase in heat transfer appears to be the result of two different interactions: (1) a resonance interaction between the acoustic oscillations and the vortices shed from the cylinder; (2) a modification of the flow in the laminar boundary layer on the upstream portion of the cylinder similar to the effect of free stream turbulence. Local heat transfer data are presented which support this hypothesis. Empirical equations are developed by means of which it is possible to calculate the maximum increase in the Nusselt number caused by a given sound wave in the second region [( Re) cf ~ 10 000].