Spot cooling of local-high heat load by high-velocity thin liquid flow was examined experimentally. Steady state experiments were conducted using a copper thin-film and rectangular sub-millimeter-channels. The width of the test channel was 2 mm. The heights of the test channel were 0.5 and 0.2 mm. The width and length of a test heater was 2 mm and 2 mm, respectively. The test liquid was degassed pure water. The liquid velocities were 1.5, 5, 10 and 15 m/s. The liquid subcooling was 20 K. Location of the heater in the test channel also was an experimental parameter: the positions of the heater from the exit of the test channel were 30 mm (middle) and 0 mm (exit). Experimental results showed that the maximum heat flux (CHF or cooling limit) during experiment with the heater at exit of the test channel was similar to that with the heater at middle of the test channel: the maximum heat flux was independent of the position of heater in the test channel. The maximum heat flux occurred when bubbles coalesced together or a dry patch appeared on the heater. The coalescence bubble covered over the heater was observed at CHF in condition of low liquid velocity. For condition of high liquid velocity, a dry patch appeared on the heater, and then the dry region extended over the heater to come around the CHF. The maximum heat flux (critical heat flux) was about 8 MW/m2 in a range of present experiments. The CHF for the present sub-millimeter channel was similar to that for conventional channel. Furthermore, models were proposed using heat transfer around a coalesced bubble and at a dry patch on a heater.

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