Influence of Contact Angle on the Internal Flow in a Freezing Water Droplet

Abstract

Ice accretion upon a surface is of interest in areas such as wind power, electric power transmission and vehicles in cold climate. Ice assimilation appears when humid air or water droplets impacts and freezes on a cold surface. In the study presented in this paper, droplets are deposited onto aluminium plates constructed to generate a specific contact angle between the droplet and substrate. Five contact angles are investigated and Particle Image Velocimetry (PIV) is used to analyse the internal flow. The droplets are studied along the vertical centerline and at horizontal lines at distances of 50% and 75% of the total height of the droplet. From the results it is found that a lower contact angle will increase the magnitude of the internal flow close to the edges. A larger contact angle will instead increase the magnitude of the flow in the center of the droplet. For a droplet with lower contact angle it was furthermore found that there is a triangular area inside the droplet with close to zero velocity.