Working performance characteristics of vacuum pump group
The Roots vacuum pump group generates heat due to the transportation and compression of gas, and the heat must be transferred from the rotor to the housing and dissipated. However, at low pressure, the heat conduction and convection performance of the gas is extremely poor, making it difficult to dissipate the heat absorbed by the rotor, resulting in the rotor temperature is always higher than the shell temperature.
Due to the thermal expansion of the rotors, the gaps between the rotors and between the rotors and the pump casing are reduced, especially when the pressure difference is also large, even the rotors are stuck and the pump is damaged. In order to make the Roots pump work under higher pressure, expand the scope of application, increase the reliability of the pump, it is necessary to dissipate the heat generated by the rotor as much as possible, that is, to cool the rotor. In order to understand the nature of air cooling, let's first look at the gas flow on the exhaust side of the Roots vacuum pump group. The suction compression process of Roots vacuum pump group is not continuous, but sudden. With the rotation of the rotor, the sucked gas is sealed in the cavity. With the rotation of the rotor, the gas in the cavity suddenly communicates with the exhaust port. Due to the high gas pressure on the exhaust side, the gas at the exhaust port will be flushed back into the cavity, and then driven out of the pump as the rotor rotates. In this process, the two rotors are vented four times per revolution.
From the above gas flow situation, it can be assumed that if the gas flushed back to the pump chamber each time is cold, the high-temperature pump chamber can absorb a large amount of heat, and the heat-absorbing gas is discharged in the continuous compression of the rotor, thereby achieving the purpose of cooling the rotor. Air cooling is based on the above principles. The exhaust port of the pump is provided with dense fins, which are cooled by a cold water pipe, or a cooling water pipe is directly installed at the exhaust port of the pump, so that the gas in the exhaust port will be cooled down. This cooling method can effectively dissipate the load generated by the Rotor of the Roots pump in the compressed gas. Moreover, when the exhaust pressure is high, due to the high density of gas molecules, the thermal conductivity is better and the cooling effect is better.
by this method,Vacuum pump unitCan operate under high pressure differential. Experiments show that the Roots pump inRunning for 6 hours under a pressure difference of 30 Torr, the temperature difference between the rotor and the housing is 22 degrees. When the cooler is installed at the exhaust port, it runs for a long time under a pressure difference of 85 Torr, and the temperature difference does not exceed 17 degrees. Generally speaking, after the Roots vacuum pump group is cooled by air, the pressure difference can be increased by 80 Torr, but it can only reach 15~30 Torr without a cooler. This cooling method is related to the ambient temperature. The higher the ambient temperature, the higher the temperature of the suction gas. The cooling effect is not good. In addition, this method can only avoid the high heat caused by the high pressure difference, but it cannot prevent the pump from heating during the compression process, resulting in a smaller gap, so it is limited by the gap of the pump itself.