Experimental study on the stagnation line heat transfer characteristics with high-velocity free slot jet impingement boiling

In this paper, the stagnation line heat transfer characteristics and critical heat flux (CHF) of small slot jet impingement boiling were experimentally investigated. Water with the Reynolds number range 34,013-136,054, the size of slot jet nozzle of 12 mm × 1 mm, and the non-dimensional nozzle to target spacing of 0.2 were used. Besides, heat transfer surface sizes were 5 mm × 1 mm and 1.5 mm × 1 mm. It was found that the stagnation line heat transfer characteristics of the jet impingement nucleate boiling in the fully developed region are irrelevant to jet velocity, subcooling and heater size for the slot jet impingement in the present experimental range. The heat transfer correlation of nickel foil heater for the jet impingement nucleate boiling in the fully developed region was obtained. Meanwhile, the CHF of the jet impingement boiling on the stagnation line was also studied. Using the experimental data to modify the semi-empirical and semi-theoretical correlation proposed previously for predicting the CHF, its modified form with heater size effect was also obtained. Through increasing jet velocity and subcooling while decreasing heater size, extremely critical heat fluxes (>108 W/m2) were achieved in the experiment, and its maximum value was 1.14 × 108 W/m2. In addition to decreasing heater size to a moderate value, it is also necessary to change heater's surface features including CA to achieve a higher heat flux.