SUMMARY

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. Considerable work has been focused on the liquid phase fluid mechanics in the Taylor cone and the behavior of the charged droplets in the ES plume as they journey from the tip of a capillary source, with a much smaller portion of the focus on the effect which these droplets impart on surfaces they impinge upon or the environment through which ES is conducted. 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. Electrospray is a desirable means of liquid delivery because of its low power consumption for production of an aerosol. The power required to drive electrospray is significantly lower than that of typical mechanical aerosol systems since mechanical spray systems experience significant frictional losses in order to generate the spray. ES is also unique in its strong dependence on strength and geometry of the applied electric field to determine sprayed droplet trajectories and velocities. This electric field can be altered rapidly in real-time, providing immediate user control over ES. With the combined promises of high efficiency, high performance, and rapid on-demand control, ES is appealing for consideration as the basis for new spray-cooling technologies. Efforts presented in this dissertation focus on improving the understanding of heat and mass transfer enhancement in nES-driven evaporative cooling of “hot-spots,” i.e., sub-millimeter areas of elevated heat dissipation. For an evaporation cooling system, the thermal resistance across a liquid film lying on the heated surface and the interrelated convection and mass transfer resistances in the gas phase are important factors for system heat transfer performance. Characterizing these key resistances requires understanding of the spray jet interaction with the heated surface, film formation and thinning, and gas-phase heat and mass transfer for volatilized coolant removal from the evaporating interface. Here, entrained gas flow visualizations, heat transfer experiments, and CFD simulations analyzed within a comprehensive thermodynamic framework provide new insights into the relevant physical phenomena.