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• Separation of two-phase ammonia has been studied in horizontal (H-H) T-junctions. • Separation in T-junction depends only on relative flow rate in certain conditions. • Simple flow pattern independent correlations are proposed for phase separation. Phase separation of a two-phase working fluid accompanies the thermal-hydraulic process in every system and device, with at least one T-junction used in a two-phase line. Adequate qualitative and quantitative prediction of phase separation in T-junction is critical for successful designing, e.g., refrigeration, thermal control, and fluid transport systems. Three simple T-junctions with different inlet and side diameters were tested in the horizontal position on two-phase ammonia at a saturation level of 40÷60 °C and mass velocities of 25÷150 kg· m −2s−1. Based on test data, it has been revealed that at the relative side branch mass flow rate above 0.6, the phase separation behaviour does not depend on inlet mass velocity, vapour quality, void fraction, flow patterns (stratified, slug and annular) and relative side branch diameter. A simplified empirical correlation has been proposed describing the ammonia test points with an error margin of ±15%. [ABSTRACT FROM AUTHOR]

• The pressure distribution and phase separation parameters of branches are analyzed. • The phase split performance between two branches is compared. • An optimal value of branches' distance is found. • The phase separation of branches reaches best when the distance is 2.0 m. • An empirical correlation is proposed to predict the split efficiency of branch. T-junction is widely used as a phase separation component to separate two-phase flow because of its simple structure and low cost. Previous studies suggest that an increase in the number of T-junction branches is conducive to raise phase separation efficiency. In this paper, the pressure distribution and phase separation performance of two-phase flow of R134a in horizontal double T-junctions are studied. The phase separation performance between two branches is compared. The parameters including inlet quality (0.3-0.6), inlet mass flow rate (10.0 g s−1-25.0 g s−1), diameter ratio (1, 0.75) and the distance between two branches (0.3 m-2.6 m) are studied. The inlet mass flow rate has significant influence on the phase separation, and the separation performance reaches best when it is 10.0 g s−1. Results show that the change of parameters has greater influence on the phase separation performance of the second branch compared with the first branch. When the distance between branches is 2.0 m, the total phase separation capacity of the branches reaches the best. By comparing the phase separation of branches, it can be found that when the distance increases gradually, the phase separation performance of the second branch first increases and then decreases, indicating that there is a specific distance that maximizes the gas phase separation efficiency of branches. The optimal distance is also related to the mass flow ratio of the second branch. Therefore, an empirical correlation equation which can accurately predict the gas phase separation efficiency of the second branch is proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

• Vapor-liquid separation of R134a/R600a at T-junctions was investigated experimentally. • Effects of inlet flow conditions were revealed. • Phase separations of mixtures and pure fluids were compared. • Effects of diameter ratio and branch angle were studied. As a promising separator, T-junction can be easily incorporated into the thermodynamic systems. Previous researches have investigated the phase separation of air-water and pure refrigerants but here the separation performance of mixtures at horizontal branch T-junctions is reported. Experiments were conducted to explore the effects of the flow conditions, the mass fractions and the geometric structures on the phase separation of R134a/R600a. During the experiments, the flow parameters including the inlet mass flux, the vapor quality and the mass flow ratio of the branch to the inlet, were varied. Three mixtures with R134a mass fraction 0.3030, 0.5202 and 0.7053 were employed. Furthermore, for the configurations of branching T-junction, the diameter ratio of the branch to the inlet was set to be 0.75 and 1.0, and three branch angles (45°, 90° and 135°) were considered. From the generated data, it was found that the branch outlet quality is always higher than the inlet quality, and the vapor fraction of branch outlet decreases with the increase of inlet vapor quality. The higher the mass flow ratio is, the larger the vapor fraction of R134a/R600a is. Under the experimental conditions, the mixtures with R134a mass fraction 0.3030 and 0.5202 have lower vapor fraction than R134a at inlet quality 0.1–0.5. As for the geometric effects, when the mass flow ratio is relatively large, more vapors usually prefer to flow into the branch with the smaller diameter, and vapor fraction for the angle 45° is lower than those for angles 90° and 135° [ABSTRACT FROM AUTHOR]

• An expander in a heat pump model showed greater COP benefit in cooling than heating. • An expander with a variable nozzle was experimentally tested. • The variable nozzle controlled pressure differential but recovered negligible energy. • Phase separation and an evaporator bypass were implemented within the expander. • Phase separation led to successful energy recovery and compressor superheat control. With increasing need for energy efficient vapor-compression cycles (VCCs), researchers have investigated different aspects of such systems to increase performance. The goal of this research is to experimentally investigate the design and control of a turbomachine expander to recover work and control the VCC. An R-410A split-system heat pump experimental setup has been utilized to compare the performance and control capabilities of a variable nozzle and a fixed nozzle with phase separation combined with evaporator bypass flow metering. A theoretical analysis on the benefit of the expander in heat pumps motivated heat pump operation in cooling mode. The variable nozzle experiments yielded a significant decrease in expander isentropic efficiency, and the evaporator bypass control led to an increase in system coefficient of performance (COP) of 2.3% with an expander overall isentropic efficiency of 18.8%. Compressor suction superheat control was achieved with the evaporator bypass over a range of ambient conditions. [ABSTRACT FROM AUTHOR]

• Based on novel distribution concept, rectifying nozzle type critical distributor (RD) is proposed. • Theoretical analysis and experimental research of RD are carried out. • Compared with Venturi distributor, RD can improve cooling capacity by more than 22.7%. In order to ensure uniform distribution of dry evaporator under various operating conditions, two novel distributors based on the distribution concept of ''flow pattern setting & critical distribution'' are proposed. The theoretical analysis and structure design of rectifying nozzle type critical distributor (RD) based on the distribution principle of ''swirling setting & critical distribution'' are carried out. And the mechanism of swirling setting and critical flow of gas-liquid two-phase refrigerant is expounded. The flow pattern setting is to adjust the up-flow non-uniform and asymmetrical flow pattern to ideal annular flow by rectifying elements, to overcome the influence of up-flow flow state on distribution characteristics. The critical distribution is to make the two-phase flow reach the local sound velocity by sonic nozzle, to overcome the influence of the non-uniform heat transfer of each branch of the downflow on distribution characteristics, and solve the influence of inconsistent resistance of each breach, pressure wave oscillation and other unfavorable factors on the heat transfer performance of the dry evaporator. Based on the results of theoretical analysis, the RD is designed, and tested on the performance test system of dry evaporator. The experimental research results show that the distribution effect of RD is the best. The cooling capacity of the dry evaporator with the RD is increased by 22.7% or more, compared with Venturi distributor. The results show that the use of RD restrain the problem of gas-liquid two phase refrigerant mal-distribution in dry evaporator. [ABSTRACT FROM AUTHOR]