Refilling and Rewetting of a Hot Horizontal Tube: Part I—Experiments

Experiments on refilling and rewetting of hot horizontal tubes indicate that gravitational effects are important and lead to flow stratification. The tube is quenched at a given location upwards from the bottom and there is a significant time lag before the top is quenched. The rewetting front is preceded by a liquid layer that is supported by film boiling and forms a “liquid tongue”. Significant pre-cooling is observed at the bottom due to the presence of this tongue. No well defined rewetting temperature exists. The channel quenches at temperatures which can vary considerably between the top and bottom of the tube, and along the tube. The results cannot be explained by a conduction controlled rewetting model. Average rewetting velocities decrease with increases in initial wall temperature, and increase with increases in inlet flow rates and subcooling. These trends are consistent with other investigations in vertical reflood. For low inlet flows and low initial wall temperatures rewetting velocities can be higher than the constant inlet liquid flow velocity. This is due to the flow stratification effect that allows the front of the liquid tongue to move with a higher initial velocity than the inlet velocity.