Experimental study on the constituent separation performance of binary zeotropic mixtures in horizontal branch T-junctions

Abstract

In this paper, the constituent separation performance of binary zeotropic mixtures, R134a/R600a, in horizontal branch T-junctions was experimentally investigated. The effects of flow conditions, mixture compositions and T-junction geometries on the constituent separation performance were studied. During the experiments, the inlet mass flux and quality were varied from 200 to 300 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 branch-inlet mass flow ratios of 0.3 and 0.5. Furthermore, constituent distributions were compared for three different inlet R134a mass fractions, namely 0.3030, 0.5202 and 0.7053. The required mass fractions of R134a at the inlet and outlet of T-junctions were calculated based on the measured liquid density. As for the T-junction geometry, the diameter ratio of the branch tube to the inlet tube was set to be 0.75 and 1.0, and three branch angles, namely 45°, 90°, 135°, were considered. In order to represent the degree of actual separation to the complete separation, constituent separation efficiency is defined as the difference of the fractions of constituents taken off in the branch. Based on the generated experimental data, it’s found that there generally exists an inflection point of separation around the vapor quality 0.2. Before the inflection point, the efficiency generally increases with the increase of inlet vapor quality. After that, the separation efficiency gradually decreases from the positive to the negative. It means that more R600a is extracted into the branch, due to the lower vapor density and vapor dynamic viscosity. Furthermore, for the three mixture compositions, R134a/R600a with an R134a fraction of 0.3030 has the best constituent separation performance. The largest variation range of outlet fraction is from 0.2559 to 0.3443 under the mass flow ratio of 0.3 and mass flux of 200 kg·m−2·s−1. However, the highest separation efficiency 9.49% is obtained under the mass flow ratio of 0.5. As for the effect of T-junction geometry, when the inlet quality is less than 0.4, increasing the diameter ratio can enhance the constituent separation. Compared with the angles 45° and 135°, the largest separation capacity is obtained by the angle 90°.