The separated oil will not enter the system with the refrigerant flow in the pipe to form the oil circulation . After the lubricating oil into the evaporator , while the low solubility due to the temperature , a portion of the lubricating oil separated from the refrigerant ; the other hand , low temperature viscosity, the separated oil tends to adhere to the tube wall, is difficult to flow. The lower the evaporation temperature, the oil return problems . This requires the design of piping and evaporator return line must be conducive to the design and construction of the oil return , a common practice is to use descent pipeline design , and ensure a greater flow rate. For particularly low temperature refrigeration systems, such as -85 ° C and -150 ° C medical cold boxes, in addition to selection of an efficient oil separator , but usually also add special solvent to prevent blocking capillaries and expansion valve lubricants , and help return oil .

 

Practice, the oil return problems due to evaporation and the return line is not uncommon for improper design . For R22 and R404A systems, 's flooded evaporator oil return is very difficult, the return line system design must be very careful. For such systems , using high oil pipeline can greatly reduce the amount of oil entering the system , effectively extending the power back to the oil return pipe no time .

 

When the compressor is higher than the position of the evaporator , the oil return pipe on the vertical bend is required . To turn back to the oil as compact as possible to reduce the deposit of oil. Spacing between the oil return bends to the right, bend back the amount of oil relatively long time, it should add some oil .

 

Variable load return line system must also be careful. When the load decreases, the return air speed will be reduced , the speed is too low is not conducive to the oil return . In order to ensure the return of oil under low load , the suction tube can be vertical double riser .

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