Flow boiling of R1233zd(E) in a horizontal tube: Experiments, assessment and correlation for asymmetric annular flow

Flow boiling heat transfer and dry-out vapor quality data for the low-GWP refrigerant R1233zd(E) are presented in this paper. Tests have been performed in a single horizontal stainless steel tube with an internal diameter of 6.0 mm for the whole range of vapor qualities (from 0.008 to 0.977) by varying the mass flux from 147 to 300 kg/m(2)s, the heat flux from 2.4 to 40.9 kW/m(2) and the saturation temperature from 24.2 to 65.2 degrees C, corresponding to a reduced pressure range of 0.036-0.125. The assessment of some available predictive methods has been performed: the best ones for the heat transfer and the dry-out predictions are both by Wojtan et al. (2005). 68.3% of the data points are falling into an error band of 30% for the heat transfer coefficients, while the MAE for the dry-out predictions is 14.4%. The range of operating conditions explored allowed to segregate the almost pure convective boiling results from those affected by nucleation. The effect of the non-uniform liquid film distribution along the perimeter has been related to the Froude vapor number: for Fr-V > 3 the pure convective boiling data are symmetric around the tube and the correlation of Cioncolini and Thome (2011) returns the best agreement (MAE = 25.4%). By using the local expression of the authors' original model, a new equation has been developed in order to capture the experimental trend also for asymmetric flows. The corrected Cioncolini and Thome (2011) method provides an overall MAE of 7.40% when compared to the entire annular flow database of this paper. (C) 2018 Elsevier Ltd. All rights reserved.