lbs/min conversion 2

[artraps]

I would like to convert x-lbs/min of air flow into x-CFM. This seems to be a simple exercise but I'm stumped. The air flow is to be measured within a 2.875 ID tunnel and I would like to use an anemometer. Got any ideas? I'll be honest here. I'm a bit ignorant on this subject.

 

[Twoballcane]

Think volume...

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”
"People get promoted when they provide value and when they build great relationships"

 

[Twoballcane]

I'm sorry think density of air...(brain not working today...must be Friday)

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”
"People get promoted when they provide value and when they build great relationships"

 

[rb1957]

how would you relate weight (or mass) to volume ?

 

[zdas04]

mass flow rate=volume flow rate / density

If you want standard conditions, the density you use has standard pressure and standard temperature. If you want actual conditions use suction pressure and suction temperature for you density calculation.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[Cockroach]

This is a mass flow, lbf/min. You are asking for a volumetric few, ft3/min or CFM. So you need some information on the air flow condition, density would be nice, but it could be upstream pressure at a temperature.

Density is mass over volume. No need to worry of time because we are saying per minute in both situations. So you need density of the flow under the said conditions.

Regards,
Cockroach

 

[DRWeig]

Just a slight correction, Cockroach -- mass flow is lb/min, not lbf/min.

Good on ya,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[IRstuff]

a previously presented equation should be:

mass flow rate=volume flow rate * density

You'll also need to have some idea of the pressure and temperature to produce a halfway accurate answer, in addition to the air velocity. Some additional information about the uniformity of flow would also be needed or assumed.

TTFN
faq731-376

 

[zdas04]

Thanks for catching that. I only do that calculation 10 times/day, MathCAD has facilitated my getting too lazy to do unit analysis on my own.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[miningman]

Unless you are at about 4000 feet above sea level or are dealing with temperatures outside 60-70 degrees farenheit , or have extreme amounts of moisture in the air, 0.075 lbs per cu foot will be quite close. All the necessary correction factors are available in a good ventilation hand book

 

[Cockroach]

Correct WRWeig, lbm/min or slugs/min. lbf would be incorrect, my apologies.

Regards,
Cockroach

 

[chicopee]

and density is a function of pressure and temperature.