Experiments on rewetting and refilling of hot horizontal tubes [1] indicate that a liquid “tongue” initially runs along the bottom causing significant precooling. The rewetting front follows this tongue, with the bottom of the tube rewetting before the top. Very little precooling is observed at the top and rewetting apparently occurs at quite high temperatures. Rewetting velocities generally decrease with increases in inlet water temperature, initial tube wall temperature and power input into the tube. Rewetting velocities increase with increases in injection flow rate. The data cannot be explained in terms of a conduction controlled rewetting model. Also the rewetting temperature varies considerably between the top and bottom of the tube, and along the tube. The phenomena appear to be hydrodynamically controlled and are well predicted by a two fluid model with reasonable constitutive equations for wall and interfacial friction, and heat transfer. The transverse gravitational force has to be incorporated in the model to account for flow stratification. The most critical constitutive relationship is with regard to the transition from film boiling to a rewet surface at the bottom of the tube. A model based on interfacial instability to signal this transition predicts the experimental results.

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