The application of ultrasound to liquid freezing got much attention over the last few years and its potential seems very promising. In order to make clear droplet freezing assisted by ultrasound

the heat and mass transfer characteristic was studied based on ultrasound theory

penetration theory of mass transfer and energy conservation. The ultrasound frequency

ultrasound intensity and operation time were studied in the process of the liquid drop freezing. The results showed that ultrasound could accelerate mass transfer and make droplet rapidly cooling. In the effect of ultrasound

the bubble size in the droplet was decreased with ultrasound frequency

and the bubble number in the droplet was increased with ultrasound frequency. Mass transfer coefficient of droplet was increased with ultrasound intensity and reduced with ultrasound frequency. For the mass transfer and heat transfer

the direction were same in the droplet freezing process

the heat transfer was strengthened by mass transfer in the droplet freezing process. Comparing with no ultrasound

droplet temperature with ultrasound (ultrasound frequency 20000 Hz and ultrasound intensity 400 W·m-2) was lower 2.0-2.5℃ after the same time (60 s). Hence the ultrasound helps to cool and freeze droplet. This study is favor to understanding the freezing by ultrasound and its application.