International Journal of Heat and Mass Transfer, Vol.140, 533-563, 2019
Flow condensation heat transfer in a smooth tube at different orientations: Experimental results and predictive models
The present study aims to better analyze the influence of body force on flow condensation heat transfer by conducting tests at multiple orientations in Earth's gravity. Dielectric FC-72 is condensed in a smooth stainless-steel tube with 7.12 mm diameter and 574.55 mm condensing length by counterflow of cooling water across the outer surface of the tube. Test conditions span FC-72 mass velocities of 50.3-360.3 kg/m(2) s, test section inlet pressures of 127.0-132.1 kPa, and test section inlet thermodynamic equilibrium qualities of 0.13-1.15. A subset of data gathered corresponding to axisymmetric, annular condensation heat transfer is identified and a detailed methodology for data reduction to calculate heat transfer coefficient presented. Uncertainty analysis is also presented and indicates channel average heat transfer coefficients are calculated within +/-3.6% to +/-26.7% (depending on operating conditions). Analysis of parametric trends for condensation heat transfer reveals the dominant influence of mass velocity (flow inertia), secondary influence of vapor mass fraction (thermodynamic equilibrium quality), and strong dependence on orientation (body force) at low mass velocities. At higher mass velocities results for all orientations investigated begin to converge, indicating body force independent annular condensation heat transfer is achieved. Separated Flow Model predictions of vertical downflow condensation heat transfer provide reasonable agreement with experimental results, evidence by a Mean Absolute Error (MAE) of 31.2%. Evaluation of condensation heat transfer correlations for horizontal flow reveal most correlations struggle for cases with high liquid content. Specific correlations are identified for superior accuracy in predicting the measured data. (C) 2019 Elsevier Ltd. All rights reserved.
Keywords:Flow condensation;Heat transfer coefficient;Body force effects;Separated flow model;Correlation evaluation