Investigation of Nucleate Boiling Mechanisms using 3D Transient Temperature Mapping

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The rapid advancement of nanotechnology and microelectronics poses significant challenges to the thermal management of extreme heat loads discharged from tightly confined areas in electrical systems. Harnessing boiling heat transfer associated with bubble growth is perhaps one of the most efficient cooling methodologies for electrical systems due to the large amount of heat removal during the phase change from water to vapor. Despite significant enhancements in heat removal rates, numerous questions remain regarding the fundamentals of bubble growth mechanisms, a major source of enhanced heat dissipation. The project goal is to develop a mechanistic model for bubble growth that lessens the risk of failure in trial-and-error tests for heat transfer enhancement. This will, in turn, provide a systematic design route for next-generation cooling systems while saving time and money. This project integrates research activities with educational goals such as offering underrepresented minority and female graduate and undergraduate students with hands-on research experiences. The research objective of this project is to accurately measure local liquid temperature distributions surrounding a growing bubble that help better explain the heat and mass transfer to bubble growth. Local fluid temperatures in the microlayer are interrogated by total internal reflection thermometry while fluid temperatures in the thermal boundary layer near the liquid-vapor interface are measured by dual-tracer laser-induced fluorescence thermometry. To capture transient temperature distributions, both techniques are combined with high-speed imaging. The transient fluid temperature data are used to quantify time-resolved heat fluxes contributing to mass transfer near the growing bubble. Comprehensive 3D temperature information is also used to validate the existing theoretical and experimental thermal transport models. This project is scientifically significant in that it illuminates the dominant heat transfer mode for fast bubble growth and therefore provides reliable methodologies to engineer surface and fluid properties for enhanced heat transfer without a trial-and-error process.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.