Ultrasound-assisted enhancement of heat transfer in immersed coil heat exchangers: Effects of acoustic intensity and ambient fluid properties

Ultrasound, as the considerable field energy source, has a significant effect on heat transfer enhancement. Although there has been deeply researched on the utilization of ultrasound in heat exchangers, the ambient environment conditions are usually ignored. In this paper, controlling vibratory surface by user defined function, the heat transfer enhancement induced by ultrasound is numerically studied in immersed coil heat exchangers, and effects of acoustic intensity, ambient pressure and ambient fluid flow velocity on the heat transfer enhancement are investigated. The results show the heat transfer enhancement factor η_h reaches to 24.26% after ultrasonic treatment for 0.005 s. When the vibratory amplitude increases from 20 μm to 35 μm, η_h raises from 15.67% to 26.71%. With an increase of the ambient pressure from 0.1 MPa to 1.0 MPa, η_h changes from 24.26% to 48.43%. While the inlet flow velocity decreases from 1.0 m/s to 0.1 m/s, η_h varies from 1.76% to 39.01%. This research based on immersed coil heat exchangers has evaluated the influence of acoustic intensity and ambient fluid properties on acoustic streaming and acoustic cavitation, which provides with a guidance in the utilization of ultrasound in heat exchangers.