Freezing of impact water droplets on cold moving substrates

Abstract

This report describes the investigation of the maximum spreading diameter of water droplets upon impacting a hydrophilic surface at different surface temperatures, impact velocities and tangential velocities. Droplet impingement has widely been the topic of interest for researchers worldwide mainly because of its vast applications in today’s world including spray cooling and anti-icing. However, under certain conditions, such as at low temperatures, droplet impingement could prove to be detrimental to the lives of the public especially in the aviation industry. Therefore, more research has to be done in this field. Using the Phantom V711 high speed camera, researchers are able to record and observe the entirety of the droplet impingement process on the surface. Furthermore, the high speed camera facilitates the analysis of the droplet impingement as it is capable of capturing images of up to a million frames per second. Thus, enabling researchers to observe and understand the droplet characteristics on the surface with ease. In this particular research, the author performed the experiment with different varying parameters. First and foremost, the experiment is done with (1) varying surface temperatures namely at -20◦, and 25◦. The surface temperature can be adjusted accordingly using the thermoelectric cooler (TEC). Next, the experiment is carried out with (2) varying impact velocities (0.75m/s, 1.25m/s and 1.75m/s) which can be controlled accurately using the KDS210 Dual syringe pump where the water droplet will be released from. Lastly, the experiment will be carried out at (3) varying tangential velocities (0m/s, 0.25m/s, 0.50m/s, 0.75m/s, 1.00m/s and 1.25m/s). This velocity refers to the speed at which the horizontal surface moves tangentially which can be controlled by the motorized linear stage (0-1.5m/s). The only parameter that is kept constant is the surface wettability of the aluminium test pieces which are prepped to be hydrophilic, maintaining a contact angle of 49.8 ± 3.4◦. Only then, will the author meticulously analyse the results and how the different conditions affect the spreading characteristics of the droplet.