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

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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.