How To Do If The Oil Return Of The Screw Chiller Is Blocked?
The reason for the poor oil return of the screw chiller is mainly due to the phenomenon of gas mixture of lubricating oil and refrigerant during operation. Specifically, during the operation of the refrigeration system, the mutual dissolution of the refrigerant and the lubricating oil of the refrigerator will cause the lubricating oil in the refrigeration compressor to run randomly and the refrigerant to be discharged into the condenser in the form of aerosol and droplet gas.
1. What are the effects of poor oil return of the screw chiller?
The poor oil return of the screw chiller will cause a large amount of lubricating oil to stay in the evaporator pipeline. When the oil film increases by 0.1mm, it will directly affect the cooling of the system. On the other hand, the machine cannot run due to lack of oil. This will lead to the accumulation of lubricating oil in the system, creating a vicious circle, increasing operating costs and reducing operating reliability.
2. How to solve the problem of poor oil return of the screw chiller?
There are two ways to return oil to the compressor, one is to return oil to the oil separator, and the other is to return the oil to the air return pipe. The oil separator is installed on the exhaust pipe of the compressor, which can generally separate 50-95% of the running oil. The oil return effect is good and the speed is fast, which greatly reduces the amount of oil entering the system pipeline, thus effectively prolonging the operation without oil return. time. For cold storage refrigeration systems with particularly long pipelines, flooded ice-making systems, and freeze-drying equipment with very low temperatures, it is not uncommon to see no oil return or very little oil return for ten or even tens of minutes after starting the machine. A bad system will cause the compressor to shut down due to low oil pressure. The installation of a high-efficiency oil separator in this refrigeration system can greatly prolong the operation time of the compressor without oil return, so that the compressor can safely pass through the crisis stage of no oil return after startup. The lubricating oil that is not separated will enter the system and flow with the refrigerant in the tube to form an oil circulation.
After the lubricating oil enters the evaporator, on the one hand, due to the low temperature and low solubility, part of the lubricating oil is separated from the refrigerant; on the other hand, the temperature is low and the viscosity is large, the separated lubricating oil is easy to adhere to the inner wall of the tube, and it is difficult to flow. The lower the evaporating temperature, the more difficult it is to return the oil. This requires that the design and construction of the evaporation pipeline and the return pipeline must be conducive to oil return. The common practice is to use a descending pipeline design and ensure a large airflow velocity. For refrigeration systems with particularly low temperature, in addition to the selection of high-efficiency oil separators, special solvents are usually added to prevent lubricating oil from blocking capillary tubes and expansion valves, and to help oil return.
3. In practical applications, oil return problems caused by improper design of evaporator and return gas pipeline are not uncommon. For R22 and R404A systems, the oil return of the flooded evaporator is very difficult, and the system oil return pipeline design must be very careful. For such a system, the use of high-efficiency oil separation can greatly reduce the amount of oil entering the system pipeline, effectively prolonging the time when the gas return pipe does not return oil after starting the machine.
When the compressor is located higher than the evaporator, the oil return bend on the vertical return pipe is necessary. The oil return trap should be as compact as possible to reduce oil storage. The spacing between the oil return bends should be appropriate. When the number of oil return bends is large, some lubricating oil should be added. Care must also be taken in the return lines of variable load systems. When the load is reduced, the air return speed will decrease, and the speed is too low, which is not conducive to oil return. In order to ensure the oil return under low load, the vertical suction pipe can use double riser.
