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Ducted air flow, Big fan VS Little fan

Ducted air flow, Big fan VS Little fan

Ducted air flow, Big fan VS Little fan

(OP)
Hello engineers,
I have 10 inch centrifugal fan extracting air through a duct. Feeding input air into the duct is a 6 inch inline fan, weaker and slower.

Is the 6 inch input fan actually slowing down the air flow because it can't spin fast enough to keep up with the air flow being sucked through it by the large fan at the other end?

Or does the small input fan add a little bit of push, slightly increasing the air flow?

RE: Ducted air flow, Big fan VS Little fan

It all depends on its fan curve which is based on fan size, speed, blade type. What you can do is plot the two fan characteristic curves (static pressure vs. CFM) and add up the two curves to get an  overall characteristic curve. The two fans being in series, you would add the static pressures
of both fan at specific CFM values

RE: Ducted air flow, Big fan VS Little fan

Or just measure the pressure in the duct near the inlet to the larger fan.  Do this with the smaller one running and off (could it be removed?).
If the pressure is higher then you have more flow.

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