Engineering Asked by Sean Ericson on January 13, 2021
I’ve been researching fans/blowers and their use in pneumatic systems (particularly conveying systems), and I’m confused by the application of density correction factors. Let me describe a sample situation:
I have a wood processing plant in which I will be using a centrifugal fan to move material through a pneumatic system. My pneumatic system is characterized by the system curve $$P_s = K_{sys} Q^2$$
where Q is the volumetric flow (CFM) and $P_s$ is the static pressure. In order to move the material through my system, I need a minimum CFM of (say) 10,000. Via my system curve, I find that this corresponds to a static pressure of (say) 7 inWC.
So, I need a fan that can supply 10,000 CFM at 7 inWC. I will do this by superimposing my system curve on the fan curves for the various fans I might select to determine the HP and RMP requirements. Here is where the density correction comes in:
My Understanding:
Ultimately, what I want is material to be moved through my system. The fan gives energy (i.e. does work) to the air, and the air in turn gives energy to the material it moves. At a given volumetric flow rate, denser air will have more energy and thus be able to do more work. Now, the 10,000 CFM I need is the flow rate needed under actual conditions (ACFM). Fan curves are calculated at standard conditions, so I should convert my ACFM to SCFM before comparing to the charts. I do this by simply multiplying by the standard/actual air density ratio.
My Question
Any references to pages/papers explaining the underlying physics would be greatly appreciated!
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