How to calculate the air volume of a Roots blower
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The last edit to this post was made by Ah on 2017-6-11 at 10:39 :handshake. The nameplate of one of the Roots pumps indicates a flow rate of 463 m3/min; however, this value can change due to variations in the inlet temperature, ambient temperature, and inlet/outlet pressures. How to calculate the actual air volume?
Calculated based on temperature and pressure under import conditions.
The actual volumetric flow rate changes very little, provided the parameters on the nameplate are accurate. The volumetric flow rate of a Roots blower has little to do with changes in the pressure difference across the blower itself; when the pressure is high, internal backflow increases, but this is generally not taken into account. Mass flow rate, which is what we sometimes refer to as volumetric flow rate, varies significantly depending on the inlet temperature, pressure, and humidity. You can calculate the density of the inlet and outlet states; multiplying this by the volumetric flow rate indicated on the nameplate gives the mass flow rate.
The actual flow rate of a Roots blower is equal to the theoretical flow rate minus the internal backflow rate. The theoretical flow rate depends on the volume created by the blower’s rotor and casing, as well as its rotational speed, while the backflow rate is related to the pressure difference between the inlet and outlet and the internal gaps. At the time of manufacture, the flow rate is typically determined using orifice plates. The flow rate of each blower varies slightly due to differences in these gaps, but the national standard allows for a variation of ±5%, which is a fairly large margin, so it usually isn’t a problem.