INSTABILITY IN THE PROPAGATION OF THE QUENCH FRONT DURING REWETTING BY BOTTOM FLOODING DUE TO EXTERNAL EXIT OBSTRUCTIONS

This study reports the periodic reversed flow and boiling fluctuations of water during the rewetting phenomenon by bottom flooding in the presence of external exit obstructions. The flow reversal and pulsations are captured by high-speed imaging, and the findings are supported from temperature responses. Two separate experimental setups are developed to investigate the phenomenon-one for imaging the flow reversal and boiling fluctuation phenomenon and the other to measure the temperature response during the flow fluctuation phenomenon. The external obstruction at the exit of the tube restricts the flow of vapor phase generated in the film boiling regime. This vapor phase creates a spike in the local pressure, thereby restricting the motion of the upward propagating quench front. As a result, the propagating front recoils and flows in the backward direction. A parametric study is carried out to investigate the influence of coolant mass flow rate and cross section of the outlet obstruction on the phenomenon of flow reversal and fluctuations created during rewetting. Experimental findings indicate that an increased coolant flow rate reduces the fluctuations in flow, while a reduced exit cross section increases the tendency of boiling fluctuations leading to delayed rewetting.