Condensation heat transfer characteristics of low-GWP refrigerants in horizontal smooth mini tube.

R1234ze, R290, R161 and R41, which regarded as refrigerants with low GWP (Global Warming Potential). Condensation of these working fluids in a horizontal smooth round tube with inner diameter of 2 mm was investigated experimentally and compared with that of R134a and R32. The condensation temperature was set as 35 °C and 40 °C. The mass flux was set from 100 kg·(m-2·s-1) to 500 kg·(m-2·s-1). HTCs (heat transfer coefficients) of R1234ze, R290, R161 and R41,are from 1-13 kW·(m-2·K-1). The condensation HTC goes up as the saturation temperature decreases and the mass flux goes up. Under the same working condition, the HTC of R161 is the highest and that of R1234ze is the lowest. The change of pressure along the tube is tested and the trend that the pressure-drop changes with the saturation temperature and the mass flux. The predicted values calculated by 7 models including Koyama model are compared with 725 experimental values. It shows that different models fit for different refrigerants, while the Koyama et al’s model is prevealing over other models.