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, R12, 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.