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Entrainment Rate of Droplets in the Ripple-Annular Regime for Small Vertical Ducts

M. A. Lopez de Bertodano, A. Assad, Stephen Beus

Nuclear Science and Engineering

Volume 129 / Number 1 / May 1998 / Pages 72-80


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Two-fluid model predictions of film dryout in annular flow are limited by the uncertainties in the constitutive relations for the entrainment rate of droplets from the liquid film. The main cause of these uncertainties is the lack of separate-effects experimental data in the range of the operating conditions in nuclear power reactors.

Air/water and Freon-113 entrainment rate data have been obtained in 10-mm tubes using the film extraction technique. These experiments have been scaled to approach high-pressure steam/water flow conditions. The effects of surface tension and density ratio, missing from most previous data sets, have been systematically tested.

The entrainment rate mechanism is assumed to be a Kelvin-Helmholtz instability. Based on this analysis and two previous correlations, a new correlation is proposed that is valid for low-viscosity fluids in small ducts in the ripple-annular regime.

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