Dynamics of acoustically levitated ice impacts on smooth and textured surfaces: Effects of surface roughness, elasticity, and structure

Abstract

Atmospheric ice collisions on exposed outdoor infrastructure are a rarely explored surface design challenge. A primary obstacle to realistic ice particles in the laboratory setting is freezing a droplet without a solid surface present and then allowing it to impact a substrate without physical intervention. Using acoustically levitated ice formation with subsequent release onto a controlled area, a third class of ice-countering system called “ice-impacting” is introduced. Stainless steel 316 (SS), epoxy resin-coated (ER), and laser-textured (LT) surfaces with known surface roughness, hardness, and structural characteristics were subjected to 40 ice droplet impacts each. The impact effect on surface properties and the effect of these properties on solid-solid interfacial impact dynamics, in turn, were examined using an analysis framework based on fundamental conservation laws. Elasticity was the most significant factor in droplet behaviour as the ER surface exhibited rebounding for 78 % of impacts, nearly double the rates of the stainless steel surfaces. However, surface roughness also played a role, particularly for droplets with rotational motion, as immobilization occurred for 66 % of impacts on the rougher LT surface. Moreover, the nanostructures on that textured surface resulted in droplet redirection perpendicular to the surface directionality. In contrast, the other surfaces experienced no consistent change in rebound angle. Elasticity also affected momentum retention: the ER surface had a translational restitution coefficient of 0.32 compared to 0.17 for the SS/LT surfaces. Surface roughness was a predominant aspect of energy retention, as the LT surface had a translational-to-rotational energy transfer coefficient of 0.07 (0.23 for the smoother surfaces), resulting in an overall energy retention coefficient of 0.09 compared to 0.28 for the SS and ER surfaces on average. The results show that the interplay between elasticity, roughness, and structure at a dynamic solid-solid interface must be considered to optimize their effectiveness when designing ice-countering surfaces.