CFM loss

[ptonsparky]

Checking out a small, 3 hp, approx 2"x18", centrifical fan that a customer wants to use for moving a reclaimed flour like substance. Using a new tool, not a toy, I checked the air flow on the 4" round inlet, 5300 fpm, and the 4" round outlet, 4300 fpm. Rounded numbers. No additional duct is attached to the fan. Where did the approx 1000 cfm go? Could multiple small?? leaks in the gasketing of the housing amount for that much loss?

 

[zbang]

What's the pressure of the output? The blower compresses the gas(air) in order to move it, so if you go from 5300 cfm at 0" pressure and increase the pressure to, say 2", the same same air is now in less space, so less cfm at the output. The compression also heats the air.

Somewhere around here I have the Buffalo Forge Fan handbook, it you're really curious.

ETA: I found this- http://www.retscreen.net/fichier.php/914/Chapter-Fans and Blowers.pdf. It doesn't download nicely (save, then rename with .pdf on the end), but it's pretty interesting.

 

[eric7379]

4" round inlet, 5300 fpm, and the 4" round outlet, 4300 fpm.

I'm sure that you meant CFM, not FPM!

 

[ptonsparky]

No, it was FPM. The CFM is just a air over the FPM with this size inlet & outlet. The fan is capable of way more, I got the curves yesterday.

zbang: Thanks for the reference. Haven't got it read yet, but it is on the list of bedtime stories.

Seems like I am doing more than just electrical for this customer but I have to find a source of power for these motors which means I have to know what size they need. They don't know. They just know what they want the results to be.

 

[Volta]

. . . moving a reclaimed flour like substance. . .

Depending on how similar to flour these particles are, be sure to fully consider Section 500.6(B)(3), and its FPN 2, and Art. 502.

 

[ptonsparky]

Hay dust. Not explosive in that a spark will set it off but blow it across an open flame...