Condensation heat transfer of R134a, R1234ze(E) and R290 on horizontal plain and enhanced titanium tubes

An experimental investigation on the condensation of R134a, R1234ze(E) and R290 outside plain and enhanced titanium tubes was conducted. The saturation temperature in the experiments was 35 degrees C to 40 degrees C, and heat flux was in the range of 8-80 kW/m(2). Effects of heat flux, refrigerant and saturation temperature on heat transfer were investigated. The heat transfer enhancement ratio of overall heat transfer coefficient decreased with increasing heat flux. It was found that the condensing heat transfer coefficient of R134a, compared with R1234ze(E) and R290, was the largest for plain and enhanced tubes. Saturation temperature had minor effect on condensing heat transfer coefficient for R134a, R1234ze(E) and R290 for plain tube. The effect of saturate temperature on the condensing heat transfer of R134a and R1234ze(E) was even negligible for enhanced tube. While, the condensing heat transfer coefficient of R290 for enhanced tube was increasing with increment of saturation temperature. Experimental condensing heat transfer coefficient were also compared with five predicting models for low-fin tube. It showed that the model of Briggs-Rose gave a better prediction result for R134a and R1234ze(E), while the model underestimated the experimental result for R290. (C) 2018 Elsevier Ltd and IIR. All rights reserved.