Mechanism of the disturbance wave generation in a vertical up- and down-ward gas-liquid two-phase annular flow.

The generation of a disturbance wave on a liquid film flowing concurrently with an up-or a down-wards gas flow in a vertical circular pipe is investigated both theoretically and experimentally and compared with that in a horizontal duct. It is made clear that the disturbance wave is generated when the velocity of liquid particles exceeds that of interfacial waves. This is similar to the case of a horizontal duct. The boundary of the existence of the disturbance wave, however, depends strongly on the gravitational force, i.e., the orientation of the pipe line and the direction of the flow in a low gas flow rate region. This is because the gravitational force affects the wave velocity but not the mean liquid flow in a horizontal line, and vice versa in a vertical line ; and also because an annular film cannot be formed in the vertical upward flow if the gas velocity is low, i.e., the interfacial shear force is small.