Simultaneous Boiling Visualization and Heat Transfer Measurement of Two Adjacent Water Impinging Jets

摘要

The effect of jet-to-jet distance of two adjacent jets on boiling heat transfer was investigated by a simultaneous boiling visualization and heat transfer measurement. The hydrodynamics of two adjacent jets were visualized by the high-speed imaging and the 4K camera on unheated surface. The surface temperature of the hot steel plate was estimated by formulating 2-D inverse heat conduction, which was measured through the flat-plate heat flux gauge. The jet Reynolds number was fixed at Re = 17,000 and the jet-to-jet distance of two adjacent jets was set to the three different jet-to-jet distances (p/d = 10, 20 and 30). The wall jet flow interference between two adjacent impinging jets forms a vertical fountain at its boundary. The more scattered water droplets are observed from the fountain due to the higher intensity at the p/d =10. The flow interaction becomes to reduce its momentum as increasing the p/d. The boiling visualization shows which boiling mode starts to occur and turns to be disappeared from film boiling to nucleate boiling on the hot surface. The measured surface temperature has a good agreement with the corresponding boiling visualization. The closer jet distance (lower p/d) shows the rapid temperature gradient along the interaction, which provides much higher cooling rate in a multiple jet nozzle when designing an intensive quenching device. [This work was supported by the KETEP grant funded by the Ministry of Trade, Industry & Energy, Korea (Grant No. 20142010102910).].