One of the most complicated issues the aerospace and aviation industries are dealing with is aircraft icing. The impact and freezing process of a water droplet on a cold surface has been investigated over time in order to develop preventative methods for avoiding icing. In the present study, we examined the behavior of a water droplet impacting on an aluminum plate with a surface roughness of 0.01µm and surface temperature variation from room temperature to 0oC, −5oC, −10oC and −15oC. The effect of droplet impact Reynolds number along with surface temperature variation on non-dimensional parameters like spread factor, retraction rate, and spread velocity is analyzed. The increase in impact Reynolds number and droplet spread factor is observed with a rise in the initial height of the droplet. At a higher Reynolds number, inertial forces are dominant over viscous and capillary forces, while at a lower Reynolds number, surface temperature shows a significant effect. The graphical representation of droplet retraction rate indicates a decrease with lower surface temperature and a rise with higher Reynolds numbers. Moreover, the spread velocity of the droplet is higher with an increased Reynolds number, and surface temperature does not have a notable effect on it. A rapid transition of momentum from vertical to horizontal direction occurs, and droplet dissipates energy in overcoming the viscous effects. The effect of surface roughness variation coupled with surface temperature is investigated in detail for three different surface roughness of aluminum and glass. The increase in surface roughness and temperature enhance hydrophobic behavior by repelling the droplet, while reduced surface temperatures show hydrophilic behavior by causing adhesion of the droplet on surface. / Master of Science / The supercool water droplets exist in the atmosphere and whenever these droplets come in contact with a cold surface, ice is formed. This ice accretion phenomena is observed not only on aircraft's control surfaces, but also on jet engines, power transmission lines and wind turbine blades. Research is on going to understand the impact and freezing process of water droplets on different cold surfaces and subsequently devise methods for avoiding this phenomena. In the current research work, the droplet impact is analyzed on an aluminum plate with surface roughness of 0.01µm. The spread factor of the droplet indicates the liquid surface contact area, and an increase is observed at larger heights in spread factor, impact velocity, and Reynolds number due to high inertia. Then, the surface temperature is varied from 0oC to −5oC, −10oC and −15oC, and it is observed that as the viscous effects are higher at lower surface temperatures, the droplet dissipates more energy in overcoming the high viscous effects and the spread factor decreases . Moreover, the spread velocity of the droplet is the measure of rate at which the liquid-solid contact area increases. Initially the droplet has vertical momentum, and on impact it shifts from vertical to horizontal direction, as the velocity rises drastically after impact. Surface roughness is another important factor that affects the ability of a surface to repel (hydrophobic) and attract (hydrophilic) the droplet by affecting its spread rate. The more the surface roughness, the droplet spread factor reduces and droplet rebounds indicating the hydrophobic nature. While adhesion is observed at the lower surface temperature, even with high roughness, showing the hydrophilic nature.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115878 |
| Date | 23 June 2023 |
| Creators | Naveed, Ahsan |
| Contributors | Aerospace and Ocean Engineering, Coutier-Delgosha, Olivier, Philen, Michael Keith, Lowe, K. Todd |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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