How to solve the problem of poor oil return of screw chiller 1. What is the cause of the poor oil return of the screw chiller? Generally speaking, the reason for the poor oil return of the screw chiller is mainly due to the phenomenon of the gas mixture of lubricating oil and refrigerant during the operation. Specifically, in the operation of the refrigeration system, encountering the miscibility of the refrigerant and the refrigerator lubricating oil will cause the lubricant in the refrigeration compressor to run and the refrigerant will be discharged into the condenser in the form of gas mist and droplets. If the effect of the oil separator is not good or the system design is not good, it will cause poor separation effects and poor oil return to the system. Of course, the previous question is that you did not use fake oil
2. What are the effects of poor oil return of screw chillers? The poor oil return of the screw chiller will cause a large amount of lubricating oil to remain 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 lacks oil and cannot be run. This will result in the accumulation of more lubricating oil in the system, causing a vicious cycle, increasing operating costs and reducing operating reliability. Under normal circumstances, refrigerant gas flow below 1% of the oil and gas mixture is allowed to circulate in the system.
3. How to solve the problem of poor oil return of screw chiller? There are two ways to return oil to the compressor: Oil separator return oil; Return to the trachea to return oil. The oil separator is installed on the compressor exhaust line, and can generally separate 50-95% of the oil. The oil return effect is good and the speed is fast. The amount of oil entering the system pipeline is greatly reduced, thereby effectively extending the operation without oil return. time. It is not uncommon for a cold storage refrigeration system with a long pipeline, a full-liquid ice-making system, and a freeze-drying equipment with a very low temperature to return to oil for a few minutes or even tens of minutes after starting up, or the amount of oil returned is very small. Bad system will cause the problem of compressor oil pressure is too low and shut down. The installation of high-efficiency oil separator in this refrigeration system can greatly extend the operation time of the compressor without oil return, so that the compressor can safely pass the crisis stage without oil return after startup. The lubricating oil that has not been 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, a 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 pipe, and the flow is difficult. The lower the evaporation temperature, the more difficult it is to return oil. This requires that the design of the evaporation pipeline and the design and construction of the return air pipeline must be conducive to oil return. The common practice is to use a descending pipeline design and ensure a large air flow speed. For refrigeration systems with particularly low temperatures, in addition to the use of high-efficiency oil separators, special solvents are usually added to prevent lubricating oil from clogging the capillaries and expansion valves and to help return oil. At the same time, some people now use the internal oil content of the air conditioner to replace the external oil content, which ostensibly saves costs, but from the perspective of the long-term cost of the system, it will only greatly increase operating costs. The efficiency of the system will become worse and worse. In practical applications, the problem of oil return due to improper design of the evaporator and the return line is not uncommon. For the R22 and R404A systems, the return of the flooded evaporator is very difficult, and the design of the return line of the system 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, effectively prolonging the time when the air return pipe does not return oil after startup.
When the compressor is higher than the position of the evaporator, the oil return bend on the vertical air return pipe is necessary. The oil return bend 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 relatively 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 return air speed will be reduced, the speed is too low is not conducive to oil return. In order to ensure the return of oil under low load, the vertical suction pipe can use double riser. And frequent compressor start is not conducive to oil return. Because the compressor stops when the continuous running time is very short, it is too late to form a stable high-speed air flow in the return air pipe, and the lubricating oil can only stay in the pipeline. If the oil return is less than that of the oil, the compressor will run out of oil. The shorter the running time, the longer the pipeline, and the more complicated the system, the more prominent the problem of oil return. Therefore, under normal circumstances, do not start the compressor frequently. Finally, the lack of oil will cause a serious lack of lubrication. The fundamental reason for the lack of oil is not how much and how fast the screw chiller runs, but the system does not return oil well. The installation of oil separator can quickly return oil and prolong the operation time of compressor without oil return. The design of the evaporator and the return air line must take oil return into consideration. Maintenance measures such as avoiding frequent start-up, defrosting regularly, replenishing refrigerant in time, and replacing wearing parts (such as bearings) in time also help to return oil. Cleaning the oil filter in time to avoid frequent start-ups, regular defrosting, timely replenishment of refrigerant, and timely replacement of wearing parts and other maintenance measures also help to return oil.
