Study On Pressure Drop And Distribution Characteristics Of Refrigerant In T-junction With Microchannel Flat Tube

The micro-channel parallel flow heat exchanger has many advantages such as compact overall structure,high heat transfer coefficient,low material cost and easy recycling.It is widely used in the field of automotive air conditioning.However,the problem of uneven refrigerant flow distribution in the microchannel parallel flow heat exchanger seriously affects the heat exchange efficiency of the heat exchanger.In order to ameliorate this phenomenon,the T-junction with microchannel flat tube is used as the basic unit of the micro-channel parallel flow heat exchanger,and the pressure drop characteristics of the single-phase flow in the T-junction with flat tube and the two-phase flow are studied through experiments and numerical simulations.The phase distribution characteristics in the T-junction with flat tube provide a theoretical basis for improving the distribution characteristics of the refrigerant in the microchannel parallel flow heat exchanger and improving the performance of the heat exchanger.For single-phase fluids,the pressure drop characteristics of refrigerant R134 a in T-junction with flat tube were experimentally studied.The results show that the irreversible pressure drop generated by single-phase flow from the header to the flat branch is mainly affected by the ratio of the header flow to the branch flow and the Reynolds number in the header,and an empirical correlation of the irreversible pressure drop coefficient is proposed.Numerical simulations have studied the influence of parameters such as header inlet flow velocity,temperature,and branch pipe insertion depth on the irreversible pressure drop.The results present that the irreversible pressure drop decreases with increasing header inlet flow rate and increases with increasing branch pipe insertion depth.The inlet temperature of the header has little effect on the irreversible pressure drop.For two-phase fluids,the phase distribution characteristics of bubbly two-phase refrigerant R134 a in the T-junction with flat tube were experimentally studied.The phase distribution characteristics in the T-junction with flat tube are mainly affected by the liquid phase inlet flow rate and inlet dryness,and the gas phase inlet flow rate has little effect on the phase distribution.When the inlet dryness of the header ranges from0.45 to 0.5,the gas-liquid distribution in the T-junction is uniform under the experimental conditions in this paper.Comparing the predicted value of the existing phase distribution model with the experimental value,the existing phase distribution model cannot accurately predict the gas-liquid separation ratio in the T-junction with flat tube.The phase distribution characteristics of conventional T-junction and the T-junction with flat tube are compared through numerical simulation.The simulation results show that under the same working conditions,the liquid phase separation ratio in the conventional T-junction will be 10% higher than that in the T-junction with flat tube,and there are two vortices in the conventional T-junction to make the phase distribution in the conventional T-junction more uniform than that of the T-junction with flat tube.The diameter of the T-junction with flat tube has little effect on the phase distribution characteristics in the tube.The liquid phase separation ratio of refrigerant R32 in the T-junction with flat tube is higher than that of R134a.