Exploiting Vapor Pressure Gradients to Suppress In-Plane Frost Growth

1604272 Boreyko，Jonathan B.冰的形成会严重损害诸如飞机、海洋结构、电网、风力涡轮机和HVAC系统等系统的机械完整性和能量效率。每年冰层形成的经济成本高达数十亿美元。除冰的有效方法包括喷洒化学品或使用电加热，但这些技术在环境和能源方面都是昂贵的。因此，能够单独抑制冰生长数小时甚至数天的表面将是非常有利的，但迄今为止，还没有这样的表面存在。该提案旨在开发智能表面，在没有任何机械或电气干预的情况下抑制冰的生长，即使在寒冷和潮湿的条件下，也能使大部分表面保持干燥。拟议的表面将有微小的结构，将引导水的沉积，以减少冰的形成。系统优化将通过模拟汽-液-冰多相系统中蒸汽传输的热力学和流体动力学来获得，这也可以揭示混合相云行为的基本见解。本建议的目的是获得一个基本的了解本地化的压力梯度和冰，水和水蒸气之间的源-汇相互作用，并利用这些知识来被动地抑制平面内的霜的生长。 采用实验、理论和计算相结合的方法，提出了以下研究任务：（1）表征液滴间霜生长：使用定制的湿度室和结合到Peltier级的疏水表面来表征冻结液滴和过冷液滴之间的面内和面外液滴间冰桥接。 所得数据将与一个不断变化的边界计算模型相关联。 (2)在冰周围形成干燥区：当水滴在周围的冷凝物有机会明显增长之前被冻结时，在冰滴和冷凝物之间形成稳定的干燥区。 一个孤立的液滴将被冻结在露点之上，然后湿度将被提高，以观察和模拟产生的干燥区。 (3)抑制平面内霜的生长：利用从前两个任务中获得的知识，将在化学和/或物理图案化的表面上形成受控的微观冰条纹阵列，使得每个冰条纹周围的干燥区域将重叠，以保持绝大多数表面干燥，不受冷凝物和霜的影响。更全面地了解液滴间蒸发和冰桥接在混合相水系统将澄清表面上霜生长的热力学和流体动力学，并提供实验洞察的Wegener-Bergeron-Findeisen过程中的混合相云的冰川作用。 此外，拟议的研究将绘制出临界相空间，其中蒸汽梯度导致冰桥与干燥区。

1604272Boreyko, 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.