Exploiting Vapor Pressure Gradients to Suppress In-Plane Frost Growth

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

1604272 Boreyko, Jonathan B. Ice formation can heavily compromise the mechanical integrity and energy efficiency of systems such as aircraft, marine structures, power grids, wind turbines, and HVAC systems. The economic cost of ice formation amounts to billions of dollars every year. Active methods of removing ice include spraying chemicals or using electric heating, but such techniques are environmentally and energetically costly. Surfaces that could, by themselves, suppress the growth of ice for many hours or even days would therefore be highly advantageous, but to date, no such surface exists. This proposal seeks to develop smart surfaces that suppress the growth of ice without any mechanical or electrical intervention, leaving the majority of the surface dry even under chilled and humid conditions. The proposed surface will have miniscule structures that will guide the deposition of water in such a way as to reduce ice formation. System optimization will be obtained by modeling the thermodynamics and fluid dynamics of vapor transfer in vapor-liquid-ice multiphase systems, which could also shed fundamental insight on the behavior of mixed-phase clouds. The objective of this proposal is to gain a fundamental understanding of the localized pressure gradients and resulting source-sink interactions between ice, water, and water vapor and to exploit this knowledge to passively suppress the in-plane growth of frost. Using a combination of experimental, theoretical, and computational techniques, the following research tasks are proposed: (1) Characterizing Inter-Droplet Frost Growth: In-plane and out-of-plane inter-droplet ice bridging between a frozen droplet and supercooled liquid droplet will be characterized using a custom-built humidity chamber and hydrophobic surfaces bonded to Peltier stages. The resulting data will be correlated with an evolving-boundary computational model. (2) Creating a Dry Zone around Ice: When a water droplet is frozen before surrounding condensate has a chance to grow appreciably, a stable dry zone forms between the ice droplet and the condensation. An isolated droplet will be frozen just above the dew point and then the humidity will be raised to observe and model the resulting dry zone. (3) Suppression of In-Plane Frost Growth: With the knowledge gained from the previous two tasks, a controlled array of microscopic stripes of ice will be formed on a chemically and/or physically patterned surface, such that the dry zone about each stripe of ice will overlap to keep the vast majority of the surface dry from condensate and frost. A fuller understanding of inter-droplet evaporation and ice bridging in mixed-phase water systems will clarify the thermodynamics and fluid dynamics of frost growth on surfaces and give experimental insight to the Wegener-Bergeron-Findeisen process of glaciation in mixed-phase clouds. Furthermore, the proposed research will map out the critical phase space where the vapor gradients result in ice bridging versus dry zones.