Flow characteristics in vertical pipes under flooding conditions

In this review, we presented contents of our three published papers on flow characteristics in vertical pipes under flooding conditions. Measurements were made at a facility of Kobe University for the falling liquid flow rate (superficial velocity J_L), pressure gradient dP/dz and void fraction α, and the wall friction factor f_w and interfacial friction factor f_i were obtained. The void fraction α data under counter-current flows are limited. Hence α and f_i were evaluated using f_w and existing dP/dz data, and correlations for α and f_i were proposed. Flow characteristics differ depending on the shapes at the top and bottom ends (square or rounded), and they were classified from the flooding location (top or bottom end). A correlation of α (liquid film thickness δ) for flooding at the top end and a correlation of f_i for flooding at the bottom end were proposed. δ under flooding conditions became thick due to the updraft of the gas flow, but it was expressed by a correlation similar to that for the free falling film. f_i is widely expressed by a function of the dimensionless liquid film thickness, but a simple f_i correlation was proposed in terms of the dimensionless gas velocity, the Kutateladze parameter K_G^*. (author)