Volume Flow Calculation 2

[jmanuelmejia]

Hello everyone, I need to calculate volume flow and I'm having a hard time doing it, help please.

A 1.5HP turbine at 3000 rpm, drives a fan, 14 inch in diameter. It takes it from ambient air to blow it into a duct heater. How much cubic feet per minute (CFM) of air does it move?

 

[cbrn]

Hi,

unfortunately it seems your question is ill-posed. You can find infinite solutions for a fan of a certain diameter, running at a certain speed, which absorbs a certain power. You have at least three unknowns here: efficiency, flow, compression ratio.

Regards

 

[sbozy25]

google the term Volumetric Flow Rate, or look in any college fluid dynamics book.

 

[TheTick]

Can you find the fan curve from the manufacturer?

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[handleman]

42

 

[MintJulep]

You are having a hard time because it can't be done if all you know is what you have told us.

Just go measure it.

Even if you have the fan curve, you will still need to measure the static pressure, so If you are measuring stuff, just measure the flow.

 

[vc66]

Agreed. Just measure the flow. It's simple, and a lot easier than trying to calculate it-especially if you're trying to do it sans some necessary variables as you seem to be.

Good Luck!

V

Mechanical Engineer/Consultant
Medical Devices
"When I am working on a problem, I do not think of beauty, but when I've finished, if the solution is not beautiful, I know it is wrong."

- R. Buckminster Fuller

 

[jmanuelmejia]

Thank you all for your answers. I would like to measure the flow, but I can't really. I'm in sales engineering, and don't have the equipment to do so... and my client, which is the one who has that application, doesn't either.

I got an answer from a friend of mine. What about wind turbine equation? taken from kinetic eq. Power=1/2*airdensity*Area*velocity^3

If I solve for velocity, and then I multiply by area, I get a flow, then convert units.

Does that sound reasonable or am I waaaaaayy off??

Thanks again everyone.

 

[MintJulep]

Waaaaaay off.

If you had efficiencies for the fan and motor you could probably reduce that to waaay off.

All you need to measure is an ammeter, some plywood, a saber saw, clear hose and water.

 

[btrueblood]

I'd add a steel rule and some food coloring. Maybe some white paint too, if you're in sales.

 

[rb1957]

i wonder if there's going to be a follow-up question ... how much airflow do i need to cool ...

as for measuring the flow speed; a leaf, a measuring tape, and a stop watch would get you pretty close ...

 

[gr2vessels]

The approx. air flow is 2800 CFM. The duct heater supplier around the corner told me so.
cheers,
gr2vessels