Experimental study on rewetting of a flat plate

Abstract

The present investigation reports the rewetting phenomenon of a flat surface where the water front approaches the centre of a heated plate from all the edges. The water front further develops a water pool above the plate surface. The typical transient temperature response for the combination of flow and developing pool boiling has been investigated. The effect of several parameters, including initial surface temperature (300 °C to 600 °C), coolant flow rate (25 g/s to 63.3 g/s) and input wall heat flux (44 kW/m2 to 66 kW/m2) on rewetting patterns have been studied. It is observed that the rewetting of the flat plate is sensitive to initial surface temperature and coolant injection flow rate. Increase in initial surface temperature and decrease in coolant injection flow rate results in delayed rewetting whereas variation in input heat flux has a marginal effect on peak surface temperature and time delay for initiation of a rewetting phenomenon. The observed physical phenomena include movement of the waterfront from plate edges towards its centre, leading waterfront edge vaporisation, detachment of water droplets from leading edge, the formation of the water pool, temporary generation of vapour columns and mist formation within the developing pool. A film boiling correlation has been proposed for predicting the heat transfer coefficients for the rewetting of a flat plate. Mass flux parameter is introduced in the correlation to address the effect of different reflooding rate, which is not prevalent in the traditional film boiling correlations. The proposed correlation can predict the heat transfer coefficient in the range of ±15% of the experimental observation.