Static pressure and airflow at reduced fan speeds

[msparks]

This is probably a stupid question but I've been going around in circles for a while now and have gotten myself completely confused.

I have a fan and a pump, with performance charts (static pressure vs. air flow) for both. I need to try and determine flow rates for each device when run at reduced speeds.

The fan/pump will be pulling a gas flow through a small tube, and exhausting to atmosphere. I know that's not the right way to use a fan, but that's what I'm stuck with right now. I can measure the pressure at the fan/pump inlet while running at different voltages.

Searching around the internet, I found that air flow is linearly proportional to fan speed and static pressure is proportional to fan speed squared.

So I'm guessing that if I'm at half the fan speed I should be at a quarter (.5²) of the static pressure. I can measure the pressure, multiply by 4 and look it up on the chart. Then take the corresponding air flow and knock it in half to get the actual flow rate.

That's a complete guess. If anyone can steer me in the right direction, I would appreciate it because I'm really stuck here. Thanks for your help.

Michael

 

[Navin A S]

Yes, you are correct in your assumption that the static pressure is proportional to fan speed squared and the airflow is linearly proportional to fan speed. Thus, if you reduce the fan speed to half, the static pressure should decrease to a quarter of the original value and the air flow should decrease to half of the original value. However, since you are running your fan/pump in an unconventional way, it would be best to actually measure the pressure and airflow at the different fan speeds to ensure accuracy.