What is the reason for the overheating of the exhaust gas of the screw air compressor?
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Author : Runningway
Update time : 2021-04-14 13:49:59
The reasons for the overheating of the exhaust of screw air compressors. Many customers know the lack of overheating of the exhaust of the screw air compressor. Overheating of the screw air compressor is a serious danger. I hope this article can help us.
The main reasons for the overheating of the exhaust temperature are as follows: high return air temperature, large heating capacity of the motor, high compression ratio, high condensation pressure, and improper refrigerant selection.
Exhaust overheating is not so messy, just because of the following reasons:
1. High return air temperature
The return air temperature unevenness is related to the evaporation temperature. In order to prevent liquid return, the return gas pipeline generally requires a return gas superheat of 20°C. Assuming that the return air pipeline is not well insulated, the superheat will far exceed 20°C. The higher the return air temperature, the higher the cylinder suction temperature and exhaust temperature. Every time the return air temperature increases by 1°C, the exhaust temperature will increase by 1 to 1.3°C.
2. Electric heating
Regarding the return air cooling type screw air compressor, the refrigerant vapor is heated by the motor when it flows through the motor cavity, and the cylinder suction temperature is once again trudged. The calorific value of the motor is affected by power and power, and the power consumption is closely related to displacement, volume power, working conditions, friction resistance and so on.
For the return air cooling type semi-hermetic screw air compressor, the temperature rise of the refrigerant in the motor cavity is planned to be between 15 and 45°C. In the air-cooled (air-cooled) screw compressor, the refrigeration does not pass through the windings, so there is no motor heating problem.
3. The tightening ratio is too high
The exhaust temperature is greatly affected by the compression ratio. The larger the compression ratio, the higher the exhaust temperature. Decreasing the compression ratio can significantly reduce the exhaust temperature. The specific methods include trekking the suction pressure and lowering the exhaust pressure.
The suction pressure is selected by the evaporation pressure and the resistance of the suction line. The evaporative temperature can be used to traverse the suction pressure, flexibly reduce the compression ratio, and then lower the exhaust temperature.
Some users think one-sidedly that the lower the evaporation temperature, the faster the cooling rate. In fact, this idea has many problems. Although lowering 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. Moreover, the lower the evaporating temperature, the lower the refrigeration coefficient, but the load increases, the working time is extended, and the power consumption will increase.
Decreasing the resistance of the return air line can also overcome the return air pressure. The specific methods include timely and better dirty return air filters, as well as reducing the length of the evaporation pipe and the return air line as much as possible. In addition, the lack of refrigerant is also a factor of low suction pressure. Compensation should be made in time after refrigerant leakage. Practice shows that reducing the exhaust temperature by trekking the suction pressure is simpler and more useful than other methods.
The primary cause of excessive exhaust pressure is that the condensing pressure is too high. Lack of heat dissipation area of the condenser, fouling, lack of cooling air or water, and too high cooling water or air temperature can cause excessive condensing pressure. It is very important to select a suitable condensing area and maintain a satisfactory cooling medium flow rate.
The high-temperature screw air compressor is designed to have a relatively low compression ratio. After being used for freezing, the compression ratio is doubled. The exhaust temperature is very high, and the cooling cannot keep up, which constitutes overheating. It is necessary to prevent the use of screw air compressors from over-planning, and to make the screw air compressors work at the smallest possible pressure ratio. In some low-temperature systems, overheating is the primary cause of defects in screw air compressors.
4. Reverse expansion and gas mixing
After the initial suction stroke, the high-pressure gas trapped in the cylinder clearance will have an inverse expansion process. After the reverse expansion, the gas pressure recovers to the inspiratory pressure, and the energy used to contract this part of the gas is lost during the reverse expansion. The smaller the clearance, on the one hand, the smaller the power consumption caused by the inverse expansion, on the other hand, the larger the air intake, which greatly increases the energy efficiency ratio of the screw air compressor. During the inverse expansion process, the gas contacts the high temperature surface of the valve plate, the top of the piston and the top of the cylinder to absorb heat, so the gas temperature will not drop to the suction temperature at the end of the inverse expansion. After the anti-swelling is over, the real inhalation process is only preliminary. After the gas enters the cylinder, on the one hand, it mixes with the inverse expansion gas, and the temperature rises; on the other hand, the mixed gas absorbs heat from the wall to increase the temperature. Therefore, the gas temperature at the initial stage of the contraction process is higher than the suction temperature. However, due to the short time for the inverse expansion process and the inhalation process, the practical temperature rise is very limited, generally lacking 5°C. Inverse expansion is caused by the cylinder clearance, which is a defect that traditional piston screw air compressors cannot avoid. If the gas in the vent hole of the valve plate cannot be discharged, there will be reverse expansion.
5. Shrink temperature rise and refrigerant varieties
Different refrigerants have different thermophysical properties, and the exhaust gas temperature rises differently after the same contraction process. Therefore, different refrigerants should be selected for different refrigeration temperatures. The mismatch of refrigerant will affect the heat dissipation coefficient of the air compressor.
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