Effect of low-frequency ultrasonic waves on heat transfer of laminar water flow over a heating flat plate

Abstract

Abstract This research investigates the effect of 40, 80, and 120 kHz ultrasound on heat transfer of laminar water flow over a heating flat plate using thin leaf thermocouples in a low turbulence water tunnel. The mainstream velocity was set at 0.127 m/s, corresponding to the local Reynolds number during 65,181 – 148,390 in the test section. The ultrasonic waves were released perpendicular to the mainstream and vertically from the upper wall at the distance of 0.15 m to the heating plate having constant heat flux of 1,040 W/m2. The results show that the ultrasound, having frequencies of 40 and 120 kHz provides the maximum Nusselt number up to 15% and 31%, respectively at the most downstream position of the test region. In the meantime, the 80 kHz waves slightly affect the heat transfer over a flat plate. Hence, in an attempt to employ the ultrasound for heat transfer enhancement over a flat plate, the distance and ultrasonic frequency must be well considered.