Condensation in horizontal tubes, part 2: new heat transfer model based on flow regimes

A new general flow pattern/flow structure based heat transfer model for condensation inside horizontal, plain tubes is proposed based on simplified flow structures of the flow regimes, and also includes the effect of liquid-vapor interfacial roughness on heat transfer. The model predicts local condensation heat transfer coefficients for the following flow regimes: annular, intermittent, stratified-wavy, fully stratified and mist flow. The new model has been compared to test data for 15 fluids (R-11, R-12, R-22, R-32, R-113, R-125, R-134a, R-236ea, a R-32/R-125 near-azeotrope, R-404A, R-410A, propane, n-butane, iso-butane and propylene) obtained in nine independent research laboratories. The new model has been tested over the following range of conditions: mass velocities from 24 to 1022 kg/(M-2 S), vapor qualities from 0.03 to 0.97, reduced pressures from 0.02 to 0.80 and tube internal diameters from 3.1 to 21.4 mm. Overall, the model predicts 85% of the heat transfer coefficients in the non-hydrocarbon database (1850 points) to within +/-20% with nearly uniform accuracy for each flow regime and predicts 75% of the entire database to within +/-20% when including the hydrocarbons (2771 points), the latter all from a single laboratory whose data had some unusual experimental trends over part of their test range. (C) 2003 Elsevier Science Ltd. All rights reserved.