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Reasons Why the Screw Chiller Does Not Return Oil

Oct. 19, 2022

Screw chiller includes water-cooled screw chiller and Air Cooled Screw Chiller. If the oil return of the screw chiller is not smooth, it is a very headache. Generally speaking, the reason for the poor oil return of the screw chiller is mainly due to the gas mixture of lubricant and refrigerant during the operation. Specifically, in the operation of the refrigeration system, encountering the mutual dissolution of the refrigerant and the lubricating oil of the refrigerator will cause the operation of the lubricant randomizer in the refrigeration compressor and the refrigerant will be discharged into the condenser in the form of aerosol and droplet gas. If the oil separator is not effective or the system design is not good, it will cause poor separation results and poor system oil return.

Air Cooled Screw Chiller

Air Cooled Screw Chiller

So what are the effects of poor oil return from the screw chiller?

The screw oil chiller has a poor oil return, which will cause a large amount of lubricant to stay in the evaporator pipe. 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 without oil and needs to be replenished. This will lead to the accumulation of more and more lubricants in the system, causing a vicious cycle, increasing operating costs and reducing operating reliability. Under normal circumstances, the circulation of refrigerant oil and gas mixtures below 1% of the refrigerant gas flow is allowed in the system.

So how to solve the problem of poor oil return of the screw chiller? The Water Cooled Screw Chiller Factory will tell you below.

There are two ways to return oil to the compressor, one is oil return from the oil separator, and the other is oil return from the return pipe. The oil separator is installed on the compressor exhaust pipeline, and can generally separate 50-95% of the oil, which has a good oil return effect and fast speed, which greatly reduces the amount of oil entering the system pipeline, thereby effectively extending the oil-free operation. time.

It is not uncommon to design a cold storage system with a long pipeline, a full-liquid ice-making system, and a very low-temperature freeze-drying equipment. It is not uncommon that the oil does not return for ten minutes or even tens of minutes after the start-up. In poor systems, the compressor oil pressure will be too low to shut down. This refrigeration system is equipped with a high-efficiency oil separator, which can greatly extend the compressor's oil-free operation time, making the compressor safe through the crisis stage without oil return after startup. 

The unseparated lubricating oil will enter the system and flow with the refrigerant in the tube, forming an oil cycle. After the lubricating oil enters the evaporator, part of the lubricating oil is separated from the refrigerant due to the low temperature and low solubility; on the other hand, the lubricating oil has a low temperature and a large viscosity, and the separated lubricating oil is easy to adhere to the inner wall of the tube, making it difficult to flow. The lower the evaporation temperature, the more difficult it is to return the oil. This requires that the design of the evaporation pipeline and the design and construction of the return gas pipeline must be conducive to oil return. A common practice is to use a descending pipeline design and ensure a large air velocity.

For refrigeration systems with extremely low temperatures, in addition to high-efficiency oil separators, special solvents are usually added to prevent lubricants from blocking the capillaries and expansion valves, and to help return oil. At the same time, some people use the built-in oil of the air conditioner to replace the external oil, which on the surface saves costs, but in terms of the long-term use of the system, it will only greatly increase operating costs. The efficiency of the system is getting worse.

The above is the reason why the Water Chiller Machine For Factory supplier introduces the reason why the screw chiller does not return oil and the countermeasures, I hope to help everyone.

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