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

Abstract

In order to evaluate effects of water levels in the upper tank h_ut 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 h_ut = 200 and 300 mm in addition to data at h_ut = 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 h_ut, and a Wallis-type CCFL correlation with the Kutateladze parameters was derived as a function of h_ut. With increasing h_ut, 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 h_ut on the liquid volume fraction α_L and the transition from α_L decrease regime to α_L increase regime with increasing the gas volumetric flux.