What is the reason for the overheating of the exhaust air of the screw air compressor?
Views : 518
Author : Runningway
Update time : 2022-01-17 16:11:33
Exhaust overheating is not that complicated. There are only a few reasons. The main reasons are as follows: electrical heating of the motor, high return air temperature, blockage of the air compressor cooler, high compression ratio and high condensing pressure, and improper refrigerant selection.
1. Electric motor heating
For the return air cooled screw air compressor, the refrigerant vapor is heated by the motor as it flows through the motor cavity, and the cylinder suction temperature is raised again. The amount of heat generated by the motor is affected by power and efficiency, while the power consumption is closely related to displacement, volumetric efficiency, operating conditions, and frictional resistance.
In the return air cooling type semi-hermetic screw air compressor, the temperature rise range of the refrigerant in the motor cavity is roughly between 15 and 45 °C. In the air-cooled (air-cooled) screw air compressor, the cooling does not pass through the winding, so there is no motor heating problem.
2. High return air temperature
The return air temperature is relative to the evaporation temperature. In order to prevent liquid backflow, the general return gas pipeline requires a return gas superheat of 20°C. If the return gas pipeline is not well insulated, the superheat degree will far exceed 20°C.
The higher the return air temperature, the higher the cylinder intake and exhaust temperature. When the return air temperature increases by 1°C, the exhaust temperature increases by 1-1.3°C.
3. The air compressor cooler is blocked
There are two phenomena of blockage of the aftercooler of the air compressor, one is carbon deposition and the other is scale.
1. Carbon deposition: carbon deposition in ventilation pipes is blocked
Since the running parts of the air compressor need the lubrication of lubricating oil, a part of the compressed air will contain lubricating oil components, and this part of lubricating oil water will coke the impurities in the lubricating oil components under high temperature conditions through the compression process. The accumulation of time, adhered to the pipe wall and other parts of the aftercooler, these black cokes are carbon deposits.
2. Scale: the blockage of the circulating scale of the air compressor
The circulating water contains various magazine elements, etc. During the long-term temperature cycle of Baidu, these components will become some sediments suspended on the copper tube wall of the after-cooler radiator, etc., which will block the copper tube over time. .
After the blockage, the internal flow of the air compressor will be blocked, and the oil will not be cooled down, so the compressor will be overheated.
4. The compression ratio is too high
The exhaust temperature is greatly affected by the compression ratio, and the larger the compression ratio, the higher the exhaust temperature. Reducing the compression ratio can significantly reduce the exhaust temperature by increasing the suction pressure and reducing the exhaust pressure.
Suction pressure is determined by evaporative pressure and suction line resistance. Increasing the evaporating temperature can effectively increase the suction pressure and rapidly reduce the compression ratio, thereby reducing the exhaust temperature.
Many air compressor users will one-sidedly believe that the lower the evaporating temperature, the faster the cooling speed. There are actually many problems with this idea. Although reducing the evaporation temperature can increase the freezing temperature difference, the cooling capacity of the screw air compressor is reduced, so the freezing speed is not necessarily fast. What's more, the lower the evaporating temperature, the lower the cooling coefficient, but the load increases, the operation time is prolonged, and the power consumption will increase.
Reducing the resistance of the return gas pipeline can also increase the return gas pressure. The specific methods include improving the dirty and blocked return gas filter in time, and reducing the length of the evaporation tube and the return gas pipeline as much as possible. In addition, insufficient refrigerant is also a factor for low suction pressure. After the refrigerant leaks, it should be replenished in time. Practice has shown that reducing the exhaust temperature by increasing the suction pressure is simpler and more effective than other methods.
The main reason for the high discharge pressure is that the condensing pressure is too high. Insufficient cooling area of the condenser, fouling, insufficient cooling air or water volume, too high cooling water or air temperature, etc., can lead to excessive condensing pressure. It is very important to choose a suitable condensation area and maintain sufficient cooling medium flow.
The operating compression ratio of the high temperature and screw air compressor design is low, and the compression ratio is doubled after being used for freezing, and the exhaust temperature is very high, but the cooling cannot keep up, resulting in overheating. The use of screw air compressors beyond the range should be avoided, and the screw air compressors should be operated at the smallest possible pressure ratio. In some cryogenic systems, overheating is the number one cause of screw compressor failure.
5. Compression temperature rise and refrigerant types
The thermophysical properties of different refrigerants are different, and the temperature rise of the exhaust gas is different after the same compression process. Therefore, different refrigerants should be used for different refrigeration temperatures.
The screw air compressor should not have overheating phenomena such as high motor temperature and high exhaust temperature during normal operation within the scope of use. Overheating of the screw air compressor is an important fault signal, indicating that there is a serious problem in the refrigeration system, or the screw air compressor is improperly used and maintained.
If the root cause of the overheating of the screw air compressor lies in the refrigeration system, the problem can only be solved by improving the design and maintenance of the refrigeration system. Replacing a new screw air compressor cannot fundamentally eliminate the overheating problem.
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