Using the method that have successfully applied in the motion for spherical bubble, the equations of motion for spherical droplets under the sonic assistance conditions are obtained.The effects of ultrasonic frequency, ultrasonic pressure magnitude, initial radius and interfacial tension on the variation of droplets radius are numerical simulated.The result shows that the vibration of droplets is enhanced and the ultrasonic pressure is increased as the decreasing of frequeucy.The droplets vibrate at their initial radius when the ultrasonic pressure magnitude is smaller than hydrostatic. The droplets will vibrate more obviously with the smaller initial radius, but the initial radius can hardly influence the last radius with the same conditions. Interfacial tension coefficient has little effect on the change of droplets radius in ultrasonic field.

interfacial tension; radius of spherical droplets; pressure amplitude; ultrasonic frequency