What's wrong with the poor oil return of industrial screw refrigerator

Poor oil return of screw chillers is a headache. Generally speaking, the main reason for poor oil return of screw chillers is the mixture of lubricating oil and refrigerant during operation.

The refrigerant and refrigerator lubricating oil are mutually dissolved during the operation of the refrigeration system, resulting in the lubricating oil and refrigerant in the refrigeration compressor being discharged into the condenser in the form of mist and micro-drop gas. Poor effect of the oil separator or improper design of the system will lead to poor effect of the separator and poor oil return of the system.

Poor oil return of the chiller in industrial production will lead to a large amount of lubricating oil retention in the evaporator pipeline. When the oil film thickness increases by 0.1mm, it will directly affect the system cooling; On the other hand, the machine can not work normally due to lack of oil, so it needs to constantly replenish lubricating oil, which leads to more and more lubricating oil in the evaporator, forming a vicious cycle, increasing operating costs and reducing operating reliability. Generally speaking, the circulation of oil and gas mixture with refrigerant gas flow less than 1% in the system is allowed.

There are two ways to return oil from the chiller compressor, one is to use the oil separator for oil return, and the other is to use the return pipe for oil return. The oil separator is installed beside the exhaust pipe of the compressor and can generally separate 50-95% of the oil. The oil return effect is good and the speed is fast, which can greatly reduce the amount of oil entering the system pipeline and effectively extend the operation time without oil return.

In practical applications, oil return problems caused by improper design of evaporator and return pipeline are not uncommon. Especially for the refrigeration system of the cold storage, the full liquid ice making system and the extremely low temperature freeze-drying equipment, for the R22 and R404A systems, the return oil of the full liquid evaporator is very difficult, and the design of the return oil pipeline of the system must be very careful. For such a system, the use of oil separator can greatly reduce the amount of oil entering the system pipeline, and effectively extend the non-return time of the return pipe after startup.

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 spacing between return pipes should be appropriate. When the number of return pipes is large, some lubricating oil should be added. The return line of the variable load system must also be careful. When the load is reduced, the air return speed will decrease, and too low speed is not conducive to oil return. In order to ensure the return oil under low load, the vertical suction pipe can use double risers.