Superhydrophobic surfaces are highly water repellent surfaces and are generated by combining microscale structuring and a hydrophobic coating such that liquids will only be in contact with a fraction of the solid surface. Their use in engineering devices occurs anywhere non-wetting surfaces are desired, although future uses are likely to be more expansive. The decrease in surface contact area between the liquid and solid phases, and thus increase in contact with a trapped gas, leads to distinct alterations of the thermal boundary conditions at the plane of the surface. Consequently, the fundamental convection physics for liquid flow over these surfaces differs drastically from classical behavior. A comprehensive understanding of the local thermal transport physics is necessary to utilize such surfaces in emerging technologies and is the primary goal of this research project. In general, it is expected that convective heat transfer coefficients will be reduced, droplets will change phase slower, and the boiling curve will be significantly altered for liquid in contact with such surfaces. The objectives of this research project are to characterize the departure from classical transport behavior due to the superhydrophobic nature of a surface. Specifically convective heat transfer is explored for: 1) Heat transfer to static liquid droplets resting on superhydrophobic surfaces, 2) Mini- and microchannel, developing and developed transport in channels with SH walls, 3) Influence on free convection dynamics for vertical SH surfaces adjacent to a liquid layer, and 4) Alteration of the classical boiling curve for liquids on SH surfaces. The research is conducted using complementary laboratory based experimental and analytical approaches to explore these topics for a range of typical superhydrophobic surface topologies. The results will be a knowledge base allowing prediction of convective heat transfer coefficients for the scenarios explored and as a function of the superhydrophobic surface topologies.
This project will explore the influence of superhydrophobicity on convective heat transfer at liquid-solid surface interfaces. Uses of superhydrophobic surfaces include self-cleaning surfaces, drag reducing surfaces, non-wetting surfaces in condensers, microfluidic manipulators in lab-on-a-chip concepts, microscale heat exchangers, and many more. For many of these, and a wide range of other potential applications, the issue of thermal transport at superhydrophobic surfaces is of fundamental importance for their implementation into high performance thermal systems. This project will advance basic knowledge related to heat transfer at superhydrophobic surfaces and provide increased understanding for implementation of such surfaces into optimized engineering devices.
