Heat and Mass Transfer Enhancement by Entrained Gas Jets in Electrospray Aerosol Plumes
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Chapman, Joel David
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Abstract
Electrospray (ES) is a phenomenon which has undergone significant scientific study, with a more than 100-year history of exploration to predict, model, and describe its behavior. Recently, interest has been garnered for the use of ES as a means of cooling electronics, motivating an investigation to better understand the physical phenomena associated with the use of ES and nES (nanoelectrospray, ES performed at nL/sec liquid flowrates) for heat dissipation via evaporative cooling. Efforts presented in this dissertation focus on improving the understanding of heat and mass transfer enhancement in ES-driven evaporative cooling of “hotspots” i.e., sub-millimeter areas of elevated heat dissipation. The fundamental understanding and quantification of the ES-driven evaporative heat transfer are achieved in this work through a combination of multi-phase flow visualization, heat transfer experiments, and CFD simulations analyzed within a comprehensive thermodynamic framework to provide new insights into the relevant physical phenomena and possible applications. It is determined that impinging electrosprayed droplets flatten liquid films which are formed on the surface of the hotspot, minimizing conduction resistance across the film. Furthermore, the electrosprayed droplets transfer momentum to the gas as they radially expand and transit toward the counter electrode, which yields a radially expanded low-velocity region of gas flow around a high-velocity central gas jet core. This gas jet impinges upon the evaporating liquid film, which reduces evaporation mass transfer resistance. When using electrospray as the means of liquid delivery, these combined effects of reduced conduction resistance and reduced mass transfer resistance yield a capability for evaporation to dissipate heat fluxes over 1 kW per square centimeter while maintaining surface temperatures below 65˚C.
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2022-04-28
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Dissertation