What is the reason for the poor oil return of screw chiller?

FR: | Author:DANNICE | Time :2023-02-02 | 351 views: | 分享到:

If the oil return of screw chiller is not smooth, it is a very headache. Generally speaking, the reason for the oil return of screw chiller is mainly because of the gas mixture of lubricating oil and refrigerant in the operation process. Specifically, in the operation of the refrigeration system, the refrigerant and the oil of the refrigerator will be missolubilized, resulting in the lubricating oil in the refrigeration compressor being discharged into the condenser with the refrigerant in the form of gas mist and microdroplets. If the oil separator effect is not good or the system design is not good, it will cause the separation effect is poor and the system return oil is not smooth. Assuming, of course, that you don't use a poor quality oil.

Screw type chiller oil return is not smooth what effect can cause?

When the oil film is increased by 0.1mm, the temperature of the system will be directly affected. On the other hand, the machine cannot run due to lack of oil, and it needs to constantly supplement the lubricating oil, which will lead to the accumulation of lubricating oil in the system, resulting in a vicious cycle, increasing operation costs and reducing operation reliability. In general, the circulation of oil and gas mixtures in the system is allowed under 1% refrigerant gas flow.

How to solve the problem of oil return of screw chiller?

There are two ways to return oil to the compressor, one is to return oil to the oil separator, the other is to return oil to the gas pipe. Oil separator installed on the compressor exhaust pipe, generally can separate 50-95% of the oil, oil return effect is good, fast, greatly reduce the amount of oil into the system pipeline, so as to effectively extend the operation time without oil return. The pipeline is particularly long cold storage refrigeration system, full liquid ice system and very low temperature freeze-drying equipment, etc., more than ten minutes or even dozens of minutes after the boot of the oil or oil return is very small situation is not rare, poor design of the system will appear compressor oil pressure is too low and stop the problem. The high efficiency oil separator installed in this refrigeration system can greatly extend the operation time of the compressor without oil return, and can make the compressor safely through the crisis stage of no oil return after startup. The lubricating oil that has not been separated will enter the system and flow with the refrigerant in the tube, forming an oil circulation. After the lubricating oil enters the evaporator, on the one hand, part of the lubricating oil is separated from the refrigerant because of the low temperature and small solubility.

On the other hand, with low temperature and high viscosity, the separated lubricating oil is easy to adhere to the tube wall, and the flow is more difficult. 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 pipe must be conducive to the return of oil. The common practice is to use the design of the down type pipeline and ensure the greater airflow speed. For particularly low temperature refrigeration system, in addition to the selection of high efficiency oil separator, usually also add special solvent, prevent oil plugging capillary and expansion valve, and help oil return. At the same time, some people use the internal oil of air conditioner to replace the external oil, which saves the cost on the surface, but from the long-term use cost of the system, it will only greatly increase the operating cost. The system becomes less and less efficient.

In practical application, the oil return problem caused by improper design of evaporator and return pipe is not rare. For R22 and R404A systems, full evaporator oil return is very difficult, the system return line design 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 prolong the return pipe after startup without oil return time.

When the compressor is higher than the evaporator, an oil return bend on the vertical return pipe is necessary. The return bend should be as compact as possible to reduce oil storage. The spacing between the oil return bends should be appropriate. The number of oil return bends is more, and some lubricating oil should be added. The return line of the variable load system must also be careful. When the load is reduced, the return speed will be reduced, too low speed is not conducive to oil return. In order to ensure oil return under low load, the vertical suction pipe can be double riser.

And the frequent start of the compressor is not conducive to oil return. Because the continuous operation time is very short, the compressor stops, and there is no time to form a stable high-speed airflow in the return pipe, and the lubricating oil can only be left in the pipeline. If the return oil is less than the rush oil, the compressor will run out of oil. The shorter the run time, the longer the line, and the more complex the system, the greater the return problem. Therefore, in general, do not frequently start the compressor.

In conclusion, the lack of oil will cause serious insufficient lubrication. The root cause of the lack of oil is not how much and how fast the screw chiller runs, but the system return is not good. Installation of oil separator can quickly return oil, prolong the operation time of the compressor without oil return. The evaporator and return pipe must be designed with oil return in mind. Maintenance measures such as avoiding frequent start-up, defrosting at regular intervals, replenishing refrigerant in time, and replacing wearing parts (such as bearings) in time also help to return oil.