Exploiting Vapor Pressure Gradients to Suppress In-Plane Frost Growth

结冰会严重影响飞机、船舶结构、电网、风力涡轮机和HVAC系统等系统的机械完整性和能源效率。每年结冰造成的经济损失高达数十亿美元。除冰的有效方法包括喷洒化学品或使用电加热，但这些技术既环保又耗能昂贵。因此，能够在数小时甚至数天内抑制冰的生长的表面是非常有利的，但到目前为止，还没有这样的表面存在。该方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。提议的表面将有微小的结构，以减少冰形成的方式引导水的沉积。通过对气-液-冰多相系统中蒸汽传递的热力学和流体动力学进行建模，可以获得系统优化，这也可以为混合相云的行为提供基本的见解。本提案的目的是获得对局部压力梯度和冰、水和水蒸气之间产生的源汇相互作用的基本理解，并利用这些知识被动地抑制霜的平面内生长。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：利用特制的湿度室和粘接在Peltier级上的疏水表面，表征冻结液滴和过冷液滴之间的面内和面外液滴间冰桥。所得数据将与一个演化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一个稳定的干燥区。一个孤立的液滴将被冻结在露点以上，然后提高湿度来观察和模拟产生的干燥区。(3)抑制面内霜的生长：利用从前两个任务中获得的知识，将在化学和/或物理图案的表面上形成一个受控的微观冰条纹阵列，这样每个冰条纹周围的干燥区将重叠，以保持绝大部分表面干燥，不受凝结水和霜的影响。更全面地了解混合相水系统中液滴间蒸发和冰桥将阐明表面结霜生长的热力学和流体动力学，并为混合相云中结冰的wegen - bergeron - findeisen过程提供实验见解。此外，拟议的研究将绘制出蒸汽梯度导致冰桥和干燥区的临界相空间。

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.