What to do if the oil return of industrial screw refrigerator is not smooth

Update:07 Jul 2021
Summary:

Generally speaking, the main reason for the poor oil re […]

Generally speaking, the main reason for the poor oil return of the screw chiller is the mixed gas of lubricating oil and refrigerant during operation.
The following introduces the reasons, hazards, and solutions for the poor oil return of the screw chiller
The refrigerant and the refrigerator lubricating oil are mutually dissolved during the operation of the refrigeration system, which causes the lubricating oil and refrigerant in the refrigeration compressor to be discharged into the condenser in the form of aerosol and micro-droplets. Poor performance of the oil-liquid separator or improper system design will result in poor separator performance and poor system oil return.
In industrial production, the poor oil return of the chiller will cause a large amount of lubricating oil to stay in the evaporator pipeline. When the oil film thickness increases by 0.1mm, it will directly affect the cooling of the system; on the other hand, the machine lacks oil and cannot work normally and needs to be constantly Replenishing lubricating oil will cause more and more lubricating oil in the evaporator, forming a vicious circle, increasing operating costs and reducing operating reliability. Generally speaking, it is permissible for an oil and gas mixture with a refrigerant gas flow rate less than 1% to circulate in the system.
There are two ways to return the oil of the chiller compressor, one is to return the oil with an oil separator, and the other is to return the oil with a return pipe. The oil separator is installed next to the compressor exhaust pipe. Generally, 50-95% of the oil can be separated. The oil return effect is good and the speed is fast. It can greatly reduce the amount of oil entering the system pipeline and effectively extend the running time without oil return. .
In practical applications, oil return problems caused by improper design of the evaporator and return line are not uncommon. Especially for cold storage refrigeration systems, flooded ice making systems, and extremely low temperature freeze-drying equipment, for R22 and R404A systems, the oil return of flooded evaporators is very difficult, and the system's oil return pipeline design must be very careful. For such a system, the use of high-efficiency oil can greatly reduce the amount of oil entering the system pipeline, and effectively extend the non-return time of the air return pipe after starting up.
When the compressor is higher than the evaporator, the oil return bend on the vertical return pipe is necessary. The oil return pipe should be as compact as possible to reduce oil storage. The distance between the oil return pipes should be appropriate. When the number of oil return pipes is large, some lubricating oil should be added. The oil return line of the variable load system must also be careful. When the load is reduced, the air return speed will decrease, too low speed is not conducive to oil return. In order to ensure the oil return under low load, the vertical suction pipe can adopt double vertical pipes.