The principle of Roots vacuum pump air cooling
2021-10-12
Summary
Roots vacuum pump for air cooling. Roots vacuum pumps generate heat by conveying and compressing gas, which needs to be transferred from the rotor to the housing. However, at low pressure, the heat conduction and convection performance of the gas is very poor, so the heat absorbed by the rotor is not easy to dissipate, resulting in the rotor temperature is always higher than the shell temperature Due to the thermal expansion of the rotor, the gap between the rotor and the rotor and between the rotor and the pump casing is reduced, especially when the pressure difference is also high, which can even cause the rotor to seize and damage the pump. In order to make the Roots pump work under high differential pressure, expand the scope of use, and improve the reliability of the pump, we need to try to dissipate the heat generated by the rotor.
Roots vacuum pumpof air cooling.Roots vacuum pumpHeat is generated by conveying and compressing the gas, which needs to be transferred from the rotor to the housing. However, at low pressure, the heat conduction and convection performance of the gas is very poor, so the heat absorbed by the rotor is not easy to dissipate, resulting in the rotor temperature is always higher than the shell temperature
Due to the thermal expansion of the rotor, the gap between the rotor and the rotor and between the rotor and the pump casing is reduced, especially when the pressure difference is also high, which can even cause the rotor to seize and damage the pump. In order to make the Roots pump work under high differential pressure, expand the scope of use, and improve the reliability of the pump, we need to try to dissipate the heat generated by the rotor, that is, to cool the rotor.
To understand the essence of air cooling, first look at itRoots vacuum pumpAirflow on the exhaust side.Roots vacuum pumpThe compression process of the suction gas is not continuous, but sudden. With the rotation of the rotor, the sucked gas is enclosed in the cavity, and with the rotation of the rotor, the gas in the cavity is suddenly connected to the exhaust port.
Due to the high gas pressure on the exhaust side, the gas at the exhaust port will rush back to the cavity and then be driven out of the pump as the rotor rotates. In this process, the two rotors are vented four times per rotation cycle.
It is conceivable from the above-described gas flow that if the gas that is backflushed to the pump chamber each time is cold, then a large amount of heat can be absorbed in the high-temperature pump chamber, and these heat-absorbing gases are discharged during the continuous compression of the rotor, thereby achieving the purpose of rotor cooling.
Air cooling is based on the above principle. The exhaust port of the pump is provided with dense fins. The cooling fins are cooled by a cold water pipe, or the cooling water pipe is directly installed at the exhaust port of the pump to cool the gas at the exhaust port. This cooling method can effectively dissipate the heat generated by the Rotor of the Roots pump in the compressed gas. In addition, when the exhaust pressure is higher, due to the higher density of gas molecules, the thermal conductivity is better and the cooling effect is better. Using this method ensures that the pump operates at high differential pressures. Experiments show that the Roots pump runs for 6 hours under a pressure difference of 30 Torr, and the temperature difference between the rotor and the housing is 22 degrees. When the cooler is installed at the exhaust port, the cooler will operate for a long time under a pressure difference of 85 torr, and the temperature difference will not exceed 17 degrees. Generally speaking,Roots vacuum pumpAfter air cooling, the pressure difference can be increased by 80 torr, and without the cooler, the pressure difference can only reach 15~30 torr.
This cooling method is related to the ambient temperature. When the ambient temperature is high, the temperature of the suction gas is high. The cooling effect is not good. In addition, this method can only avoid the high heat generated by the high pressure difference, but cannot prevent the heat generated by the pump during the compression process, resulting in a small gap, so it is limited by the gap of the pump itself.
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