Numerical Analysis Of Refrigerant And Oil In Vertical U Tube

The direct-expansion heat pump (DXHP) is a special kind of ground-source heat pump which uses a buried copper piping network through which refrigerant is circulated. Refrigeration heat transfer directly to the soil to reduce the heat exchange loop and improve the energy utilization. However,the system's long pipe,large fall and lot's of oil store places due to lubricant hard to return to compressor. Underground heat exchanger is the core to design a DXHP because of it's important status。It is more difficult to raise the oil against gravity so that the refrigerant vapor must have a sufficiently high velocity to ensure the refrigerant vapor velocity greater than the minimum refrigerant velocity when design up pipe.In this paper,temperature distribution,import pressure of compressor, pressure of expansion valve outlet of U-tube changes with time is evaluated.To simulate the flow of refrigerant and oil in the underground U-tube:set up flow mathematical model of refrigerant oil mixture based on the refrigerant oil mixture physical propertiesjudge the existence within the state of oil by numerical simulation of refrigerant flow inside the tube,and finally establish the oil return model to analyze the refrigerant pipe steam minimum speed. It shows that mathematical model of refrigerant oil mixture is correct by compared simulation results with the experimental measurement data. The conclusion shows that the minimum refrigerant oil return velocity is 3.348 m/s when diameter is 12.7mm and mass flow is 0.01668 kg/s.To calculate the minimum refrigerant velocity by changing the diameter of ground heat exchanger and the refrigerant mass flow when the other parameters unchanged. The minimum refrigerant velocity is increase when diameter increase but as mass flow decreases. the minimum refrigerant oil return velocity is 3-10m/s in diameter range of 10-50 mm.the change with mass flow is not significantly.This work has some theoretical significance on the direct expansion ground source heat pump research.