ENTRAINMENT IN VERTICAL GAS-LIQUID ANNULAR FLOWS

The film height, the pressure drop and the fraction of liquid entrained in annular two-phase vertical flows are examined. Measurements were made in 2.29 cm and 4.2 cm pipes for liquid viscosities, from 1.1 to 4.6 cp, and gas densities, from 1.3 x 10('-3) to 3.24 x 10('-3) g/cm('3). The results are correlated with film height, pressure drop and entrainment models developed by previous investigators.; A separated flow approach, in which the film and the core, including the gas and the entrained droplets, are treated as distinct phases, is used to analyze the film height and the frictional pressure drop measurements. For low liquid flow rates the film height is found to be lower than Henstock's laminar flow relation. In addition, the frictional pressure loss is found to vary with the film height made dimensionless with respect to the gas phase friction velocity and kinematic viscosity, m(,g)('+), rather than with m/D(,t) assumed by Henstock and Hanratty (1976).; Stability equations which are derived from the momentum equation and a mass balance on the liquid film are applied to predict the wavelength of the ripple waves and to predict the roll wave transition. The observed average wavelength of the ripples is found to be twice the predicted wavelength. This is due to the breaking up of the observed ripple waves. For high gas velocities and liquids with viscosities of 4.6 cp or less, the roll wave transition coincides with the critical film flow rate below which no atomization occurs and can be correlated with the fluid properties group, (mu)(,L)(rho)(,G)(' 1/2)/(mu)(,G)(rho)(,L)(' 1/2). This correlation is important for the development of an entrainment relation.; The entrainment correlation is based on an equilibrium relationship between the rate of atomization of droplets from the film surface and the rate of deposition of droplets onto the film. After initiation of atomization, entrainment increases with the third power of the gas velocity. At very high gas velocities a fully entrained condition is reach for which further increases in the gas velocity do not cause a decrease in the flow rate of the wall film. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI...