鉛直管内でのフラッディング状態における管内流動特性

Abstract

Counter-current flow limitation (CCFL), the void fraction α, the wall friction factor fw, and the interfacial friction factor fi depend on the shapes of the top and bottom ends of vertical pipes, i.e., the sharp top end and round bottom end (SR), round top end and sharp bottom end (RS), and round top and bottom ends (RR). We observed flow structures with a high-speed video camera and measured CCFL (the relationship between superficial velocities of up-flow gas and down-flow liquid), pressure gradient dP/dz, and α in a RR vertical pipe with the diameter of 20 mm, and working fluids of air and water under flooding conditions, and we obtained fw and fi by using the annular flow model. The feature of flow structures in RR was occurrence of disturbance waves inside the vertical pipe, while they mainly appear at the bottom end in SR and RS. The liquid volume fraction (1−α), dimensionless pressure gradient −(dP/dz) * , and fi in RR for rough film were the same as those for rough film in SR and RS. (1−α), −(dP/dz) * , fw, and fi in RR for smooth film were close to those in SR for smooth film but they were larger than those in SR due to larger falling liquid volume fraction. The upward velocity of disturbance waves was also discussed.

Gas-liquid Interfacial Friction Factor under Flooding Conditions in Vertical Pipes

“…The experimental setup and method were the same as those previously reported [5][6][7][9][10]. In this study, the shape of the top and bottom ends of the test section was sharp-edged (S/S).…”

“…Based on the one-dimensional annular flow model, force balance equations for the gas core and the entire cross section are respectively expressed by: (7) ( 8) and (9) where |dP/dz| * is the dimensionless pressure gradient, and αL (= 1−αG) is the liquid volume fraction. The fw and fi can be obtained from Eqs.…”

“…They evaluated liquid film thickness δf, fw and fi, and proposed correlations of δf, fw and fi for SF [7,8]. Finally, Sano et al [9] carried out air-water experiments using a vertical pipe of D = 20 mm with rounded top and bottom ends (R/R), and measured CCFL characteristics in the pipe (CCFL-P), dP/dz and αG. They showed that fw and fi were different depending on the combination of the shapes (sharp-edged or rounded) at the top and bottom ends.…”

“…Takaki et al [10] carried out air-water experiments using a vertical pipe of D = 40 mm with the rounded top and bottom ends (R/R), and measured CCFL characteristics, dP/dz and αG. They obtained fw and fi, and derived a correlation for fw, which did not classify the flow state, using the previously measured data with D = 20 mm [5,6,9] and D = 40 mm [5,7,10].…”

“…The results were compared with those obtained with other combinations of the shapes (sharp-edged or rounded) at the top and bottom ends (R/S, S/R, and R/R). From the results of those experiments [5][6][7][9][10] and this experiment, we obtained a fi correlation for all flow states including SF and RF, and we evaluated the effect of the fi correlation on the prediction of αG.…”