ANALYSIS OF ANNULAR TWO-PHASE FLOW WITH LIQUID ENTRAINMENT (MIXING LENGTH MODEL, HORIZONTAL, PRESSURE DROP, FILM THICKNESS)

A differential model for adiabatic annular gas-liquid two-phase flow with liquid entrainment has been developed by postulating a mixing length distribution in the turbulent flow region, across both the liquid and the core phases. The model is based on a modified form of the single-phase mixing length function to account for turbulence intensity attenuation due to the presence of entrained liquid droplets in the gas core and the presence of the core-film interface. The shear stress-velocity gradient relationships are integrated numerically by using the complete shear stress distribution to produce the velocity profile which in turn is integrated to obtain the flow rates of each phase.;Simultaneous predictions of pressure drop and average film thickness for given flow rates show good agreement with a wide range of experimental results obtained by different groups of investigators.;Predicted velocity profiles in the core region also compare well with data.;The model includes a new treatment of the characteristic shear stress in the laminar wall layer that makes it possible to predict flow rates in vertical flow at the point of zero wall shear stress in agreement with limited experimental results.;A nondimensional form of the model is used to handle different fluids and tube diameters. It predicts both co-current upwards and downwards flows passing smoothly through the region of countercurrent flow and horizontal flows without any special treatment of the interface. The flow characteristics obtained by this model resemble those obtained by other models, especially those based on the interfacial friction factor. It is shown that the interfacial friction factor can be predicted from the mixing length distribution (and vice versa).