Minichannels (those with channel spacing near 1 mm) offer an attractive scale range for technological applications of two phase cooling. They are small enough to create large heat fluxes, but large enough to remove significant quantities of heat. Furthermore, they do not present the fouling and maintenance concerns as do microscale channels. Heat transfer coefficients can be very high due to the latent heat consumed during vapor production, and to enhanced near wall mixing caused by bubbles which are constrained to remain near the channel surfaces. Intellectual Merit: This research uses liquid crystal thermography in concert with high speed video imaging to investigate highly subcooled bubbly flow within a millimeter scale channel. In this flow regime, swarms of very small contracting bubbles are swept along by the flow, presenting the opportunity for greatly increased cooling caused by the capacity of the bubbles to efficiently move subcooled liquid from the core of the channel toward the walls. The insight gathered from this experimental investigation will provide the basis for a better understanding of the physics of subcooled bubbly flow in minichannels, and this understanding will lead to new models of this important regime. Broader Impacts: The technological broader impact of the research is its contribution to the discovery and understanding of thermal processes and performance limiting phenomena in two phase mm scale devices. Students involved in the project will develop capabilities in demand in high technology industries: experimentation involving small scale devices, high speed digital imaging, liquid crystal thermography, and experience with two phase cooling systems. Experience shows that the visual impact of high speed imaging and liquid crystal thermography generates interest in students and often motivates them to pursue graduate study. Using this research as the vehicle, minority students, Hispanic students in particular, will be recruited into graduate level study through direct involvement as undergraduate Honors thesis students. The laboratory also participates in several College of Engineering recruiting activities designed to attract students into engineering, namely the Engineering Open House and the Engineering Leadership Day.
