The ultra-low temperature freezer will fail after a long period of use, and the user needs special attention when oil return occurs.
In the ultra-low temperature freezer, the oil return is not smooth, which will cause a large amount of lubricating oil to stay in the evaporator pipe. When the oil film is increased by 0.1mm, it will directly affect the system cooling. On the other hand, the machine lacks oil and cannot run, and it is necessary to continuously replenish the lubricating oil. This will result in more lubricants in the system, resulting in vicious cycles, increased operating costs, and reduced operational reliability.
There are two ways to return oil to the compressor. One is to return the oil to the oil separator, and the other is to return the oil to the return line. The oil separator is installed on the exhaust pipe of the compressor, and has good oil returning effect and high speed, which greatly reduces the amount of oil entering the system pipeline, thereby effectively prolonging the oil return running time.
The ultra-low temperature freezer cabinet has a particularly long cold storage refrigeration system, a full-liquid ice-making system, and a lyophilized device with a very low temperature. It does not return oil or has a very small amount of oil after ten minutes or even tens of minutes after the start-up. Rarely, a poorly designed system will have a problem that the compressor oil pressure is too low and the machine is shut down. This type of refrigeration system is equipped with a high-efficiency oil separator that can greatly extend the compressor's non-returning operation time, so that the compressor safety is not returned after the start-up. The crisis phase.
Lubricating oil that has not been separated from the ultra-low temperature freezer 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, the solubility is low due to low temperature, and a part of the lubricating oil is separated from the refrigerant; on the other hand, the temperature is low and the viscosity is large, and the separated lubricating oil is likely to adhere to the inner wall of the pipe, and the flow is difficult.
For refrigeration systems with extremely low temperatures in ultra-low temperature freezer cabinets, in addition to high-efficiency oil separators, special solvents are usually added to prevent the lubricating oil from plugging the capillary and expansion valve and helping to return oil. At the same time, some people use the built-in oil of the air conditioner to replace the external oil, which saves the cost on the surface, but in terms of the long-term use cost of the system, it will only greatly increase the operating expenses.
The oil return of the flooded evaporator is very difficult, and the design of the system return line must be very careful. For such a system, the use of high-efficiency oil can greatly reduce the amount of oil entering the system piping, effectively extending the return time of the return air pipe after starting. When the ultra-low temperature freezer compressor is higher than the evaporator, the oil return bend on the vertical return pipe is necessary. The oil return bend should be as compact as possible to reduce oil deposits. The spacing between the oil return bends should be appropriate. When the number of oil return bends is relatively large, some lubricants should be added.
Since the continuous operation time of the ultra-low temperature freezer is very short, the compressor stops, and the return air pipe does not have a stable high-speed airflow, and the lubricating oil can only remain in the pipeline. If the oil is less than the oil, the compressor will be short of oil. The shorter the running time, the longer the pipeline, the more complicated the system, and the more serious the oil return problem. Therefore, in general, do not start the compressor frequently.
If the ultra-low temperature freezer is short of oil, it will not work effectively, so the above faults need to be solved in time.