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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]

• A 3D numerical model is built for R134a two-phase distribution in a T-junction. • Mechanisms of two-phase distribution are analyzed under different flow patterns. • The fraction of gas flowing through the branch decreases as inlet quality increases. • An increase in pressure difference at the junction diverts more liquid to the branch. The maldistribution of gas-liquid two-phase flow will decline the efficiency of the refrigeration system as the heat transfer performance of the heat exchangers decreases. The distribution characteristics of gas-liquid two-phase flow of refrigerant mixtures R134a in the vertically-upward T-junction were investigated in this work by 3D numerical simulation using the Eulerian model. The simulations were conducted for inlet quality from 0.005 to 0.8 and inlet mass flux from 100 to 1000 kg·m−2s−1 at a saturated temperature of 272.0 K, respectively. The effect of inlet quality on the two-phase flow distribution was studied when the inlet flow patterns were intermittent flow, annular flow, stratified-wave flow, and mist flow, respectively. The fractions of the gas phase and liquid phase flowing to the branch were used to represent the gas and liquid phase distribution characteristics in the T-junction. Numerical results showed that the fraction of the gas phase flowing through the branch decreased with an increase in inlet quality within the scope of this study. The distribution uniformity of the liquid phase in the vertically-upward T-junction was the best for mist flow and the worst for stratified-wave flow at the inlet. Calculation results indicated that a decrease in the difference in the inertia forces acting on the two phases would promote the uniformity of the gas phase distribution in the vertically-upward T-junction and an increase in pressure difference at the intersection zone would lead to a larger amount of liquid phase diverting to the branch. [ABSTRACT FROM AUTHOR]

• In run pipe, "descend-ascend" of static and total pressure happens under high F. • The local pressure drops of R1234yf, R600a and R245fa increase in turn. • An ANN predicting model of local pressure drop was established. • Sensitivity analysis of flow parameters on K 12J and K 13J was conducted. The two-phase flow behaviors in T-junction are quite complex in energy transport systems. In this paper, the two-phase flow pressure drop of refrigerants in a horizontal branching T-junction was analyzed numerically and predicted using artificial neural network. Firstly, the distribution of static and total pressure was obtained based on Eulerian method, and the parametric studies on the local pressure drop were conducted. It is observed that the vortexes in the entrance of branch pipe lead to the pressure fluctuation and irreversible pressure losses, and the "descend-ascend" of static and total pressure happens under high mass flow split ratio in run pipe. Then, the ANN predicting model of local pressure drop coefficients was established. It shows that GA-BPNN and PSO-BPNN has the best predicting ability for K 12J and K 13J respectively, and the relative errors are within 10% for most cases. Finally, the sensitivity analysis was conducted, indicating that the effect of mass flow split ratio (F) and inlet quality (x 1) is the most significant for K 12J and K 13J respectively. [ABSTRACT FROM AUTHOR]

• Simulation on constituent separation and mass transfer in T-junction is performed. • Numerical simulation with mass transfer is compared to that without mass transfer. • The influence of the quality at inlet on the constituent separation is studied. • Flow characteristic and mass transfer of base case are discussed. • A correlation of mass transfer for annular flow in T-junction is proposed. The study of constituent separation in T-junction is important to realize the operation of the constituent adjustable system. This paper presents a numerical simulation on the constituent separation and mass transfer of R134a and R600a in T-junction. The multiphase flow model of volume of fluid (VOF) is adopted, and the interphase mass transfer of R134a and R600a is achieved by adding source terms in governing equations. The quality at inlet varies from 0.51 to 0.92. The mass flow rate at inlet and flow rate weighting of branch outlet are 10 g⋅s−1 and 0.3, respectively. Results show that the error of numerical simulation with mass transfer is lower than that of numerical simulation without mass transfer. When the quality at inlet is 0.81, the error of numerical simulation with mass transfer can be reduced by 50.07% compared with the numerical simulation without mass transfer. The higher the quality at inlet, the higher the separation efficiency of R134a when the quality at inlet is less than 0.81. When the quality at inlet is 0.81, the separation efficiency of R134a in the numerical simulation with mass transfer is the largest, whose value is 1.47%. Most of the flow patterns are annular flow. The pressure and flow pattern have an important influence on the constituent separation and the interphase mass transfer rate. A correlation with 10% error band of interphase mass transfer for annular flow in T-junction is proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

T-junction of high-pressure pipe which is formed by common hot forging has the disadvantages of low material utilization rate, large machining allowance and high cost, and so on. In order to improve the material utilization rate, product quality and disclose the law of precise forging. In this study, the forming method by closed-die forging technology to produce T-junction of high-pressure pipe on special press machine was put forward, a threeaxis directional closed-die forging die was designed.Through the numerical simulation analysis of the forming process of junction of high-pressure pipe by Deform-3D software, the velocity field and equivalent strain field of the forming process were obtained, and the metal forming flow law was analyzed to predict the forging force. Results demonstrate that the whole forming technology can be divided into three stages: reverse upsetting, radial extrusion and combined extrusion. The final forming contour is clear and the filling is full with no folding, insufficient filling and uneven flow line. Based on the analysis of forming load, it is predicted that forging force is about 13,000 Kn. The mold design of the study is novel, the process is reasonable, and the forming quality is excellent. The proposed method provides a good prospect to determine the precise forging technique of T- junction of high-pressure pipe. [ABSTRACT FROM AUTHOR]