Entrained liquid fraction prediction in adiabatic and evaporating annular two-phase flow

A new method to predict the entrained liquid fraction in annular two-phase flow is presented. The underlying experimental database contains 2460 data points collected from 38 different literature studies for 8 different gas-liquid or vapor-liquid combinations (R12, R113, water-steam, water-air, genklene-air, ethanol-air, water-helium, silicon-air), tube diameters from 5.0 mm to 95.3 mm, pressures from 0.1 to 20.0 MPa and covers both adiabatic and evaporating flow conditions, circular and non-circular channels and vertical upflow, vertical downflow and horizontal flow conditions. Annular flows are regarded here as a special form of a liquid atomization process, where a high velocity confined spray, composed by the gas phase and entrained liquid droplets, flows in the center of the channel dragging and atomizing the annular liquid film that streams along the channel wall. Correspondingly, the liquid film flow is assumed to be shear-driven and the energy required to drive the liquid atomization is assumed to be provided in the form of kinetic energy of the droplet-laden gas core flow, so that the liquid film-gas core aerodynamic interaction is ultimately assumed to control the liquid disintegration process. As such, the new prediction method is based on the core flow Weber number, representing the ratio of the disrupting aerodynamic force to the surface tension retaining force, a single and physically plausible dimensionless group. The new prediction method is explicit, fully stand-alone and reproduces the available data better than existing empirical correlations, including in particular measurements carried out in evaporating flow conditions of relevance for boiling water nuclear reactor cooling. (C) 2011 Elsevier B.V. All rights reserved.