Effects of Water Levels in Upper Tank on Flow Characteristics in a Vertical Pipe under Flooding at Its Top End

In order to evaluate effects of water levels in the upper tank hut on flow characteristics in a vertical pipe under flooding at its top end, counter-current flow limitation (CCFL characteristics), void fraction and pressure gradient were measured for counter-current flows of air and water in a vertical pipe with the diameter of 40 mm at hut = 200 and 300 mm in addition to data at hut = 100 mm measured in our previous study, and the wall and interfacial friction factors were obtained from the data. As a result, the falling water flow rate decreased with increasing hut, and a Wallis-type CCFL correlation with the Kutateladze parameters was derived as a function of hut. With increasing hut, the thickness of the falling water film decreased due to decrease in the falling water flow rate, and the wall and interfacial friction factors decreased due to decrease in the water film thickness. The annular flow model with correlations for CCFL, and the wall and interfacial friction factors could predict the effects of hut on the liquid volume fraction αL and the transition from αL decrease regime to αL increase regime with increasing the gas volumetric flux.