Abstract:

ESDU 90024 develops a prediction procedure for pressure drop in annular/dispersed flow. It does not apply at the bottom of a condenser, where there is slug flow or the condensate flows as a falling film. However the pressure drop in this region is small. The method used is to predict the pressure drop using existing correlations for two-phase adiabatic flow (Friedel with roughness correction for the frictional component, Premoli et al to establish the vapour density/liquid density ratio and hence the gravitational component, and homogeneous theory for the momentum component). Correction factors on that prediction are developed by comparing results with experimental data extracted from the literature covering a wide range of diameter, pressure, quality, mass and heat fluxes, and density ratio. Values are tabulated of the correction factor applying for given ranges of density ratio, quality and condensation number (heat flux divided by the product of mass flux times latent heat of vaporisation). Also tabulated with each value are the number of points used and the standard deviation. A step-by-step calculation process is set out and illustrated with a worked example. See ESDU 93014 for a Fortran program of this calculation method. In practice, the pressure drop at inlet to the tubes of a condenser dominates, and it is shown how it may be estimated using ESDU 89012.