Effects of Diameters on Flow Characteristics in Vertical Pipes under Flooding Conditions

In our previous studies, we carried out air-water counter-current flow experiments under flooding conditions in vertical pipes having a diameter of D = 40 mm with combinations of sharp-edged or rounded top and bottom ends, and we measured counter-current flow limitation (CCFL), pressure gradient dP/dz, and void fraction αG. We obtained the wall and interfacial friction factors fw and fi, and proposed correlations for fw and fi. In the present study, we carried out similar experiments in vertical pipes of D = 60 mm with rounded top and sharp-edged or rounded bottom ends (R/S or R/R) to evaluate effects of diameters on flow characteristics. For the smooth film (SF) due to flooding at the top end in the region of low superficial gas velocity JG, the |dP/dz| value was very small and the wall friction term was large. The liquid film thickness δf could be expressed by the previously proposed correlation. For the rough film (RF) due to flooding at the bottom end in the region of high JG, no significant difference was observed for fw and fi between D = 40 and 60 mm. We confirmed that CCFL characteristics at the lower end (CCFL-L) with R/S could be expressed by the Kutateladze parameters in the range of D = 40-60 mm and the characteristics were those for large diameters in the region of D ≥ 40 mm.