Summary: for a good refrigeration system, in addition to the matching of compressor, condenser, evaporator and throttling device, the pipeline design needs to be reasonable. How important is pipeline design? As a professional engineer of refrigeration system, the headache should be the oil return problem of the system. During the normal operation of the system, a small amount of oil will continue to leave the compressor with the exhaust. When the system pipeline 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, it will have a negative impact on the efficiency of the condenser and evaporator; The oil returned to the compressor is less than the oil leaving the compressor, resulting in the loss of the compressor
A good refrigeration system requires reasonable pipeline design in addition to matching the compressor, condenser, evaporator and throttling device.
How important is pipeline design? As a professional engineer of refrigeration system, the headache should be the oil return problem of the system. During the normal operation of the system, a small amount of oil will continue to leave the compressor with the exhaust. When the system pipeline 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, it will have a negative impact on the efficiency of the condenser and evaporator; The oil returned to the compressor is less than the oil leaving the compressor, which eventually damages the compressor; When filling the compressor, the oil level can only be maintained for a short time; Only the correct pipeline design can maintain the good oil balance of the system and achieve the safe operation of the system.
1、 Suction pipeline design
1. The horizontal suction pipeline shall have a slope greater than 0.5% along the flow direction of cooling air;
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, ensure that the gas flow rate is not less than 7.6-12m/s;
4. The gas flow rate greater than 12m / s can not significantly improve the oil return, resulting in high noise and high pressure drop of suction pipeline;
5. A U-shaped oil return bend shall be set at the bottom of each vertical suction pipeline;
6. If the height of the vertical suction pipeline exceeds 5m, a U-shaped oil return bend shall be set every 5m;
7. The length of U-shaped oil return bend shall be as short as possible to avoid excessive oil accumulation;
2、 Design of evaporator suction pipeline
1. When the system does not adopt evacuation cycle, a U-shaped interception bend shall be set at the outlet of each evaporator. To prevent the liquid refrigerant from flowing into the compressor under the action of gravity during shutdown;
2. When the suction riser is connected with the evaporator, a section of horizontal pipe and intercepting bend shall be reserved in the middle to install the temperature sensing package; Prevent misoperation of expansion valve.
3、 Exhaust pipeline design
When the installation position of the condenser is higher than that of the compressor, a U-bend is required at the outlet of the air inlet pipe of the condenser to prevent oil from returning to the exhaust side of the compressor during shutdown and to prevent liquid refrigerant from flowing back from the condenser to the compressor.
4、 Liquid pipeline design
1. The liquid pipeline usually has no special restrictions on the flow rate of refrigerant. When the solenoid valve is used, the flow rate of refrigerant shall be less than 1.5m/s;
2. Ensure that the refrigerant entering the expansion valve is supercooled liquid;
3. When the pressure of liquid refrigerant drops to its saturation pressure, some refrigerant will flash into gas.
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