The present study measured the effects of the ambient temperature and substrate surface on the freezing process of a water droplet. We built the experimental setup for the measurement of the droplet freezing process in a low-temperature test chamber. An air pressure controller was used to control the pressure inside the droplet generator to produce water droplets. Then

a camera recorded the details of the droplet freezing process. The results showed that the heat conductivity coefficient of the substrate surface had a significant influence on the freezing time. When the ambient temperature was -22.0 ℃

the freezing time of the droplets on red copper was 3.8 s and the freezing time of droplets on stainless steel was 5.0 s

both of which were less than the 15.2 s measured for the glass surface. In addition

despite the appearance of protrusions during the water droplet freezing process in all the cases

the collapsing bulge phenomenon happened only in the glass surface case.