Experimental study on phase separation of refrigerant at horizontal T-junction

In this paper, the phase redistribution of refrigerant two-phase flow at a horizontal branch T-junction was investigated experimentally. The T-junction had equal-sized inlet and outlet tubes (internal diameter 8.0 mm). During the experiments, three refrigerants, namely R134a, R600a and R245fa were considered. The inlet mass flux and quality were varied from 200 to 500 kg m−2 s−1 and from 0.1 to 0.9, respectively. Meanwhile, the mass flux of the branch was regulated by keeping the mass flow ratios to 0.3, 0.5 and 0.7. Under these experimental conditions, intermittent and annular flows at the T-junction inlet were identified and predicted. After analyzing the experimental data, it was found that the vapor is preferred to flow into the branch. As the inlet quality increases, the fraction of vapor extracted into the branch decreases, whereas the mass flux has little influence on the phase redistribution of refrigerant under the same flow pattern. Furthermore, a higher vapor fraction can be obtained by a larger mass flow ratio. For the effect of refrigerant on the phase separation, the vapor faction of the branch satisfies the following order: R245fa > R600a > R134a. The product of momentum ratio and viscosity ratio between vapor and liquid is defined to characterize the phase separation degree of refrigerant qualitatively. In order to test the applicability of the published models in the literature, the present data are compared with the predicted values. The results show that the models for air-water are not appropriate to predict the phase redistribution of refrigerant two-phase flow at the T-junction. A separation model for refrigerant should be proposed by coupling with the pressure drop.