Enhancement of cooling rate during rapid quenching of a thin horizontal wire by ultrasonic vibration

The effect of ultrasonic vibration on heat transfer during rapid quenching of 0.3 and 0.5 mm dia. horizontal platinum wires was studied experimentally using water and ethanol as test liquids. The frequencies of ultrasonic vibration ν were 24 and 44 kHz. The power input to the transducer P ranged from 10 to 280 W. The falling velocity of the wire was set at 0.6 and 1.0 m/s. The initial wire temperature ranged from 500 to 1 200 K and the liquid subcooling from 40 to 70 K. The wall superheat at the first minimum heat flux point (M1 point) initially increased with increasing P and approached a constant value at high P. The heat flux after the M1 point increased considerably due to the application of ultrasonic vibration. The effect of ultrasonic vibration was more significant for ν = 24 kHz at high subcooling. In order to understand the mechanism of heat transfer enhancement, the distributions of sound pressure and cavitation intensity in the liquid pool were also measured. The heat transfer enhancement showed a close correlation with the effective value of sound pressure.