Vertical upward cocurrent gas-liquid annular flow

Upward cocurrent gas‐liquid annular flow was investigated in a 50.8 mm ID cylindrical vertical pipe. The film flow was studied by measuring instantaneous local film thickness, wall shear stress, and pressure gradient. Analysis of these data revealed that at low gas flow rates the film motion is controlled by a switching mechanism, as speculated by Moalem‐Maron and Dukler (1984). In the region of high gas flow rates the switching process is suppressed and traveling roll waves characterize the film motion.