Experimental study on instantaneously shedding frozen water droplets from cold vertical surface by ultrasonic vibration

• Ultrasonic vibration is introduced to remove frozen droplets from cold surface.
• Frozen water droplets can be instantaneously removed by ultrasonic vibration.
• The mechanical effect and the acoustic pressure effect are the dominant reason.
• Heating effect has limited effect on the frozen water droplets removal.

The ultrasonic vibration is introduced to remove adherent frozen water droplets from cold surface, which provides the possibilities for effective defrosting. The shedding processes of various frozen water droplets adhered to 70 mm × 70 mm cold vertical surface by 20 kHz and 60 W ultrasonic vibration were experimentally studied. It was found that the frozen water droplets instantaneously crack and shed off from the vertical surface due to the combined effects of interface transverse shear force generated by ultrasonic mechanical vibration and impact force induced by ultrasonic acoustic pressure. However, the heating effect triggered by ultrasonic vibration has limited effect on the frozen water droplets removal. Moreover, the frozen water droplets in different diameters within 2–30 mm can be successfully removed and all the frozen water droplets in different positions of 70 mm × 70 mm cold surface can be completely shed off by 20 kHz high frequency ultrasonic vibration. The results showed that the ultrasonic vibration has a very strong ability to remove the frozen water droplets, which are the parasitic substrates for frosting, from cold flat surface and thus it is a highly potential defrosting method for practical application.