Heat transfer processes in patterned and rough microchannels

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Any practical surface is rough, with the roughness extending over several scales - from the atomic scale to that observable to the naked eye. The proposed work aims to investigate how the influence of such characteristics would modify fluid (liquid or gas) flow. For example, roughness could be related to a hydrophobic aspect, where liquid would skim along the surface at a larger velocity (with less friction and needing less driving force and energy) compared to a smooth surface. For a heated liquid, such larger velocity may imply larger heat transfer. However, the roughness on the surface is also comprised of air of low thermal conductivity, which would be expected to reduce the efficacy of heat transfer. Through such considerations, the amount and rate of heat transfer may be sensitively regulated by controlling the amount of roughness and will be studied, experimentally and theoretically, in this work. The consequent greater understanding obtained would yield fundamental scientific insights into roughness, friction, and the control of heat. It is also aimed to translate such insights to the immediate design of microscale pipes and flows, with applications ranging from the cooling of electronic components and devices to biomedical diagnostics. Longer-term applications to enhancing the efficiency of fluid flow, lubrication, and water filtering, with respect to reducing drag and heat transfer across the interface are being considered. The overarching goal is to gain quantitative understanding of multiphase flow and heat transfer over rough surfaces. The project will investigate the influence of nano- and micro-scale surface effects in modulating measurable macroscale properties such as temperature, pumping power, and heat transfer, with very wide ranging consequences. From an experimental point, the project mainly involves the: (a) development and analysis of patterned/rough superhydrophobic surfaces, and (b) measurement of velocity profiles and effective heat transfer coefficients in such surface constituted channel flow, in concert with theoretical model validation. It is concurrently aimed to develop and implement the theoretical and numerical tools for modeling multiphase flow and heat transfer over ordered and spatiotemporally disordered surfaces. Probabilistic frameworks and stochastic mapping of random flow domains will be used to model the inherent variability of the surfaces and the resulting flows. The research would substantially extend the state of the art in thermal transport modeling involving ordered surfaces to random nanostructured surfaces. The tuning of thermal transport processes, considered through the theoretical and experimental efforts, would enable higher efficiency micro-/nano-fluidics with a wide range of physical, chemical, and biological applications.