What is the problem with poor oil return for the 2 ton water chiller?

What is the problem with poor oil return for the 2 ton water chiller?

Generally speaking, the main reason for the poor oil return of LC -25°C ~ -5°C Low Temperature Chillers is the gas mixture phenomenon of lubricating oil and refrigerant during operation. Specifically, during the operation of the refrigeration system, encountering the mutual solubility of refrigerant and refrigerator lubricating oil can cause the lubricating oil in the refrigeration compressor to be discharged into the condenser in the form of mist and droplets with the refrigerant during machine operation.

If the oil separator is not effective or the system design is not good, it will cause poor separation effect and poor system oil return. Of course, the previous question was that you did not use fake oil.

If the oil return of the screw chiller is not smooth, it will cause a large amount of lubricating oil to be trapped 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 is unable to operate due to oil shortage and needs to be continuously replenished with lubricating oil. This will lead to an accumulation of lubricating oil in the system, causing a vicious cycle, increasing operating costs, and reducing operational reliability. In general, it is allowed for the oil gas mixture to circulate in the system with a refrigerant gas flow rate of less than 1%.

There are generally two situations for compressor oil return, one is the oil separator oil return, and the other is the return pipe oil return.

The oil separator is usually installed on the exhaust pipeline of the compressor, which can achieve 50-95% oil flow. It not only has a good oil return effect, but also has a fast speed, which can reduce the amount of oil entering the system pipeline and prolong the operation time without oil return.

For some equipment, due to the long pipeline, the oil return time after startup may be quite long, which may take ten to even ten minutes. Many times, due to poor pipeline design, the compressor oil pressure is too low and the compressor stops. For this situation, installing an oil separator can effectively solve the problem of the compressor running without oil return for a long time.

After the lubricating oil that has not been separated enters the system, it flows together with the refrigerant in the pipe, forming an oil cycle. When lubricating oil enters the evaporator, due to low temperature and low solubility, a portion of the lubricating oil is separated from the refrigerant. In addition, at low temperatures, the difficulty of the oil increases, and the separated lubricating oil is easier to adhere to the inner wall of the pipe, making it difficult to flow.

The lower the evaporation temperature, the more difficult it is to return oil. This requires that when designing the evaporator pipeline, the return air pipeline should be helpful for returning oil. A common practice is to use a drop type pipeline design to ensure high airflow speed.

For low-temperature refrigeration systems, in order to solve the problem of poor oil return, in addition to using an oil separator, special solvents can also be used to avoid lubricating oil blocking the expansion valve and capillary.

In practical use, it is not common for the evaporator and return air pipeline to cause poor oil return. Therefore, it can be considered from the perspective of cooling load and utility. For refrigeration systems with long operating hours at low loads, it is recommended to choose screw compressors. If the compressor is installed higher than the evaporator, there should be a return oil bend on the return air pipeline, and the design of the return oil bend should be compact to reduce oil storage, At the same time, the spacing between the return bends should be reasonable. If there are many return bends, lubricating oil can be added appropriately.