A systematic experimental study on the evaporation rate of supercooled water droplets at subzero temperatures and varying relative humidity

Supercooled water droplets (SWD) are present in clouds at high altitude and subjected to very low temperatures and high relative humidity. These droplets exist in a metastable state. The understanding of the evaporation of SWD at these extreme conditions is of high interest to understand rain, snow, and hail generating mechanisms in clouds. This paper focuses on the experimental results of the measurements of the evaporation rates \(\beta\) of supercooled water droplets. For this purpose, single SWDs are trapped by means of optical levitation. During the evaporation process, the elastically scattered light in the forward regime is recorded and evaluated. Experiments have been performed for different relative humidities \(\phi\) at three constant ambient temperatures, namely, \({T_\infty }=268.15;~263.15;~253.15~{\text{K}}\) (\({t_\infty } = -5;\,-10;\,-20~^{\circ}{\text{C}}\)). The experimental data agrees well with direct numerical simulations (DNS) carried out with the in-house code Free Surface 3D (FS3D) and shows that the use of a simplified model is permissible for these ambient conditions.