EAGER: Control and mitigation of frost formation using mixed hydrophilic and hydrophobic surfaces

[1448270]堪萨斯州立大学贝茨霜和冰的形成会对飞机的安全性和可靠性以及风力涡轮机的发电产生严重后果。在15年的时间里，74起失去控制的飞机坠毁事故中有20起是由于机翼结冰造成的。此外，环境保护署估计，美国机场每年的除冰费用约为5亿美元。消除或减少飞机机翼和控制面上结冰量的表面可以使航空更安全，成本更低。这项工作探索了一种使用疏水（拒水）和亲水（亲水）涂层来改变表面特性并防止冰形成的技术。已经有研究表明，这些疏水和亲水表面使表面冻结的时间是普通金属表面的20倍。为了制作更好的抗结冰表面，有必要更好地理解为什么这是有效的。由于霜冻形成是生活在较冷气候的人们的共同经历，这是K-12活动的一个极好的项目。这项工作包括堪萨斯州立大学多元文化工程项目的教育推广工作，为初中、高中和本科生中代表性不足的群体提供推广项目，以及在堪萨斯州儿童探索中心为5-9岁的儿童创建示范和实验室。目前，大多数的减霜研究都集中在超疏水表面，因为它可以降低结霜所需的温度和增加所需的冻结时间。然而，这些表面的减缓效应可能对实验条件和表面结构极为敏感。这项工作的目的是研究具有混合亲水和疏水区域的表面的潜力，以减轻和控制霜的形成。在混合润湿性表面上，由于成核所需的能量垒较低，霜将优先在亲水性区域形成。因此，通过选择性地对具有不同润湿性的表面进行图案化，可以控制霜核的大小、形状和位置。假设控制霜的成核不仅会影响成核温度和冻结时间，还会影响霜的密度、生长速度和结构。表面将在不同的静态和流动条件下使用堪萨斯州立大学的环境室进行测试。表面将用珀尔帖冷却器冷却。将使用共聚焦显微镜获得1微米分辨率的霜冻成核和生长的三维图像。得到的结果将导致关系式的公式，以预测霜的形成行为作为一个函数的亲水点的大小和方向。这些关系将用于更新模型，以设计更复杂的减霜表面。此外，初步结果表明，与疏水性表面相比，具有混合润湿性的表面显著增加了冷凝液滴在表面冻结所需的时间。这可能是由于疏水/亲水界面改变了表面附近水分子的取向，需要输入额外的能量来将分子重新定向到所需的晶体结构。这项工作还将研究接触线数量和长度增加的表面，以确定对冻结时间的影响。

1448270Betz, Kansas State UniversityThe formation of frost and ice can have severe consequences on aircraft safety and reliability, and wind turbine power production. Over a fifteen year period, 20 of 74 control loss airplane crashes were due to icing on aircraft wings. Additionally, the Environmental Protection Agency estimates that deicing costs US airports approximately $500,000,000 each year. Surfaces that eliminate or reduce the amount of ice formed on airplane wings and control surfaces could make aviation safer and less expensive. This work explores a technique using hydrophobic (water-repellant) and hydrophilic (water-loving) coatings to change surface properties and prevent the formation of ice. Already, it has been shown that these hydrophobic and hydrophilic surfaces delay surface freezing by twenty times that of normal, metal surfaces. It is necessary to better understand why this works in order to make even better surfaces which resist icing. Since frost formation is a common experience for people living in cooler climates, it is an excellent project for K-12 activities. This work includes educational outreach efforts with the Multicultural Engineering Program at Kansas State University, in outreach programs for underrepresented groups in middle school, high school, and undergraduate students, as well creating demonstrations and labs at the Kansas Children's Discovery Center for children ages 5-9. Currently, most research in frost mitigation is focused on superhydrophobic surfaces which can decrease the temperature required for frost formation and increase the required freezing time. However, the mitigation effects of these surfaces can be extremely sensitive to experimental conditions and surface structure. The objective of this work is to investigate the potential of surfaces with mixed hydrophilic and hydrophobic regions to mitigate and control frost formation. On a mixed wettability surface, frost will preferentially form on hydrophilic areas, due to the lower energy barrier required for nucleation. Therefore, by selectively patterning a surface with various wettabilities, the size, shape, and location of frost nucleation can be controlled. The hypothesis is that controlling frost nucleation will not only affect the nucleation temperature and freezing time but also the density, growth rate, and structure of frost. Surfaces will be tested under varying quiescent and flow conditions using environmental chambers at Kansas State University. The surface will be cooled with a Peltier cooler. A confocal microscope will be used to obtain 3-D images, with 1 micron resolution, of frost nucleation and growth. The results obtained will lead to the formulation of relationships to predict the frost formation behavior as a function of the hydrophilic spot size and orientation. These relationships will be used to update models for designing more sophisticated frost mitigating surfaces. Additionally, preliminary results have shown that surfaces with mixed wettability significantly increase the time required for condensed droplets to freeze on the surface compared to a hydrophobic surfaces. This may be due to the hydrophobic/hydrophilic interface changing the orientation of water molecules near the surface, requiring the input of additional energy to reorient the molecules into the desired crystalline structure. This work will also investigate surface with an increasing the number and length of contact lines to determine the effect on freezing time.