Droplet freezing phase transition and heat transfer under the ultrasonic effect

Abstract

Ultrasound-assisted freezing technology is getting more attention among researchers due to its outstanding behavior in improving freezing performance. However, the lack of reliable thermo-physical model has prevented its widespread usage in related fields. As demonstrated in this study, a physical model of frozen droplet was established based on the local conservation of energy, which presented the changing rules of droplet's thermal-mass properties including porosity, exchanged heat, and liquid proportion. The variation of the droplet's liquid proportion with no ultrasound, time-controlled ultrasound, and whole-process ultrasound was analyzed, respectively. According to the calculation results, the loading of ultrasound in the droplet's frozen process had the potential to considerably increase the phase transition rate. In particular, the droplets' completely freezing time with the loading of time-controlled ultrasound, whole-process ultrasound, and without ultrasound was 13.5 s, 14.1 s, and 14.6 s, respectively. The maximum relative error of mathematical and experimental results was 6.16%, and the minimum error was 2.96%. This paper contributes to a comprehensive understanding of the ultrasonic effect in improving freezing efficiency and controlling the phase transition process.