JET IMPINGEMENT BOILING IN HOT SURFACES WELL ABOVE THE LIMITING TEMPERATURE FOR SOLID-LIQUID CONTACT

摘要

Jet impingement boiling phenomena in hot surfaces were investigated by means of temperature measurements and video records. A 2-mm water jet of 5-80 K subcooling and of 3-15 m/s velocity was impinged on the flat surface of a cylindrical steel or brass block that was preheated to 400-600℃. During the quench, the transient temperature responses of 16 thermocouples embedded in two depths beneath the surface were recorded to estimate surface temperature by an inverse heat conduction technique. A high-speed video camera was also employed to capture images of boiling and flow phenomena. Sometimes the flow became explosiveoisy and sometimes very calm and quiet. Different flow patterns, as identified from video images, resulted from the interactions between the jet and vapor bubbles formed atear the impinging surface. The flow patterns are found to be dependent on the block material and its surface temperature. It is also found that for a certain period of time, the surface temperature (T_w) remains well above the thermodynamic limiting temperature (T_(max)) for solid-liquid contact. The cooling curves at the center of the impinging surface for different experimental conditions are explained in relation to the limiting temperature. A theoretical approach to elucidate the early-stage phenomena is also outlined in this study.