Experimental investigation of the effect of stable magnetic field on droplet freezing

In this study, the effect of magnetic field on droplet freezing was investigated based on a visualization system. Possible influencing factors on droplet freezing, such as magnetic field intensity, cold surface temperature, and droplet volume, were considered in this study. During the two stages of droplet supercooling and freezing process, the changes of the droplet internal temperature, the formation of initial crystal nucleus, and the freezing time were observed. Experimental results show that in comparison with the non-magnetic surface, the supercooling degree of droplets was increased in the range of 150–300 mT magnetic field intensity, thereby prolonging the freezing time of droplets. Particularly, the droplet was best suppressed on a cold surface with 250 mT magnetic field intensity. The freezing time of droplets was prolonged by 132.0 %. However, the droplets were accelerated to freeze on the cold surface with magnetic field intensities of 350 mT and 400 mT. Droplet freezing on cold surfaces was also affected by surface temperature and droplet volume. As the surface temperature of magnetic cooling dropped from −10 °C to −20 °C, the ability of the magnetic field to inhibit droplet freezing would be gradually weakened. With the increase of droplet volume from 20 μL to 50 μL, the initial freezing time of droplets was shortened. These results are related to the influence of magnetic field on the nucleation process and hydrogen bond in the water molecular cluster.