As a professional engineer who has worked in a refrigeration system, the most troublesome problem should be the oil return problem of the system. When the system is running normally, a small amount of oil will continue to leave the compressor with the exhaust gas. When the system piping is well designed, the oil will return to the compressor, and the compressor can be fully lubricated; if there is too much oil in the system, Negatively affects the efficiency of the condenser and evaporator; less oil returning to the compressor than leaving the compressor, eventually damaging the compressor; refueling the compressor, only maintains oil level for a short time; only correct piping Only by designing, can the system have a good oil balance, and then the safe operation of the system can be achieved.
First. Design of suction pipeline
1. The horizontal suction pipeline should have a slope of more than 0.5% along the direction of the refrigerant gas flow;
2. The cross section of the horizontal suction pipeline must ensure that the gas flow rate is not less than 3.6m/s;
3. In the vertical suction pipeline, the gas flow rate must be ensured not less than 7.6-12m/s;
4. The gas flow rate greater than 12m/s cannot significantly improve the oil return, which will produce high noise and lead to a high pressure drop in the suction line;
5. At the bottom of each vertical suction line, a U-shaped oil return must be set up;
6. If the height of the vertical suction line exceeds 5m, a U-shaped oil return must be set up for every additional 5m;
7. The length of the U-shaped oil return bend should be as short as possible to avoid excessive oil accumulation;
Second, the evaporator suction pipeline design
1. When the system does not use the evacuation cycle, a U-shaped trap should be set at the outlet of each evaporator. To prevent liquid refrigerant from flowing into the compressor under the action of gravity during shutdown;
2. When the suction riser pipe is connected to the evaporator, there should be a horizontal pipe and an interception bend in the middle, so that the temperature sensor can be installed bravely; to prevent the expansion valve from malfunctioning.
Third, Design of exhaust pipe
When the condenser is installed higher than the compressor, a U-bend is required at the inlet of the condenser to prevent oil from returning to the discharge side of the compressor during shutdown, and also helps prevent liquid refrigerant from flowing from the condenser. flow back to the compressor.
Four, liquid pipeline design
1. The liquid pipeline usually has no special restrictions on the flow rate of the refrigerant. When a solenoid valve is used, the flow rate of the refrigerant should be lower than 1.5m/s;
2. Ensure that the refrigerant entering the expansion valve is a subcooled liquid;
3. When the liquid refrigerant pressure drops to its saturation pressure, a portion of the refrigerant will flash into a gas.
Post time: Jul-09-2022