Rewetting of hot vertical tubes by a falling liquid film with different directions of venting the generated steam

An experimental study of quenching of a hot vertical tube by sudden introduction of a falling liquid film was investigated under different methods of venting the generated steam. The steam generated during the quenching process may form a countercurrent vapor velocity which exceeds the onset of flooding limit causing flooding of the liquid film and resisting the propagation of the quench front delaying the rewetting process. To study the effect of this steam countercurrent flow, experiments were carried out in three stages. In the first stage, the tube was closed from top to force the steam generated to be vented from bottom. In the second stage, both ends of the tube were opened to allow venting of the steam from both ends. In the third stage, the tube was closed at bottom and the steam was vented from top. The results showed that, the rewetting velocity in case of bottom steam-venting is higher than that in case of top and bottom steam-venting which in turn is higher than that in case of top steam-venting. For the three methods of steam venting, the quenching velocity decreases with increasing the initial tube temperature and the inlet liquid temperature and decreasing the liquid flow rate. Experimental correlations for rewetting velocities were deduced from experimental data for different cases of steam venting directions. Predictions of equations were compared with the present and previous experimental data and good agreement was found.