Experimental Study of Acoustically Enhanced Heat-Transfer from Copper Sphere in a Steady Flow Field

Abstract

The combined effects of acoustic field and flow field on the forced convective heat transfer rate during cooling of a stationary sphere were investigated experimentally. The acoustic frequency is in the range of 100 to 2500 Hz, with the velocity ratio of acoustic velocity and flow velocity is in the range of 0.59 to 4.76. The relationship among sound pressure levels, frequency, flow velocity and the diameter of the sphere with the temperature gradient of the sphere were analyzed. The results show that higher velocity ratio cause higher heat-transfer rate. However, when the sphere size is 5 mm, the heat transfer rate is always lower than that without an acoustic field during our experiment, and when the sphere size is 10 mm and the velocity ratio is higher than 3.38, the heat transfer rate is higher than that without an acoustic field, but when the size of the copper sphere is 15 mm, the velocity ratio is decreased to 1.89. There is a special frequency, at which Nu reaches a maximum. This special frequency increases with increasing SPLs. The conclusions highlight a good application prospect in combustion for the boiler.