Exploiting Vapor Pressure Gradients to Suppress In-Plane Frost Growth

结冰会严重损害飞机、海洋结构、电网、风力涡轮机和暖通空调系统等系统的机械完整性和能源效率。每年结冰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上都很昂贵。因此，能够在几个小时甚至几天内抑制冰生长的表面将是非常有利的，但到目前为止，还不存在这样的表面。这项提议旨在开发智能表面，在没有任何机械或电气干预的情况下抑制冰的增长，即使在寒冷和潮湿的条件下，表面的大部分也会保持干燥。拟建的表面将具有微小的结构，将引导水的沉积，从而减少冰层的形成。通过对蒸汽-液体-冰多相系统中蒸汽传输的热力学和流体动力学进行建模，将获得系统优化，这也可以为混合相云的行为提供基本的见解。这一建议的目的是从根本上了解冰、水和水汽之间的局域压力梯度和由此产生的源-汇相互作用，并利用这一知识被动地抑制霜层内的增长。利用实验、理论和计算相结合的方法，提出了以下研究任务：(1)表征液滴间霜冻生长：将使用定制的湿度室和粘结在Peltier级上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的桥接。由此产生的数据将与一个不断演变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液有机会明显增长之前被冻结时，在冰滴和冷凝物之间形成一个稳定的干燥区。一个孤立的液滴将被冻结在露点上方，然后提高湿度，以观察和模拟由此产生的干燥区。(3)抑制面内结霜：利用从前两项任务中获得的知识，将在化学和/或物理图案的表面上形成受控的微观冰条阵列，使每条冰条周围的干燥区重叠，以保持绝大多数表面干燥，防止凝结和霜冻。更全面地了解混合相水系统中液滴间蒸发和冰桥接将有助于阐明表面结霜的热力学和流体动力学，并为混合相云中冰川形成的Wegener-Bergeron-Findeisen过程提供实验依据。此外，拟议的研究将绘制出水汽梯度导致冰桥与干区的临界相空间。

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.