Shape and temperature dependence on the directional velocity change in a freezing water droplet

Abstract

Freezing of water droplets are of interest in areas such as de-icing and anti-icing of wind turbine blades, aircrafts and cars. On part of the ice build-up that has been less studied is the internal flow in water droplets and how it affects the freezing process. In this paper the aim is to investigate how the contact angle, substrate composition and temperature influences the internal flow. Particle Image Velocimetry (PIV) is used to determine the magnitude and direction of the internal flow, with specific emphasis on directional changes. Results show that a larger contact angle will increase the internal velocity, freezing time and time until the directional change. Cooler substrate temperature increase the internal velocity while reducing the freezing time, but the dependence on the time until the directional change is not as pronounced. The result thus indicate differences in the driving forces between freezing time, internal velocity and directional velocity change. Difference due to substrate composition, i.e. mixture of ice and metal versus only metal is furthermore compared.

Keywords

• Internal flow
• Water droplet
• Freezing
• PIV
• Directional change