Quantitative liquid crystal thermography was used to investigate boiling incipience and nucleate flow boiling in rectangular mini-channels with channel heights of 2 mm to 500 μm. Distributions of surface temperature along the heated surface were measured from the liquid crystal images, and streamwise profiles of heat transfer coefficient on the heated surface were calculated. The working fluid was the refrigerant R-11. Observations of the boiling incipience superheat excursion, the hysteresis phenomenon, and saturated flow boiling are presented. Comparisons to established two-phase heat transfer correlations are performed to investigate the existence of “thin channel” effects.

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