3000 BTU's will raise 2640 CFM of air, from 100¦F to What, in 1 Min?

[DM2]

I'm trying to determine what the temperature rise will be of a 1 cu. ft. of air, moving at 2640 CFM, when exposed to a flame emitting 3000 BTU's. The volume of air is introduced at standard pressure and at 100°F.

The situation is this:
I have an open flame that was calculated to have an output of 3000 BTU's. Approximately 100 feet away from this flame, I have some material that will fail at a given temperature (haven't been told what that temp is yet). This is an outdoor environment and I don't really know what the air movement is so for now I’m assumption that it's 2640 CFM (30 mph). I'm thinking this isn't much different than a heating system for a house. The heating systems give off X Btu's which should raise the temperature X °F, from a given temperature.

Can someone help me figure this out?


Regards,
Dan Marr

http://www.advantagefireprotection.com

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[IRstuff]

30 mph = 44 ft/s, which means that a single cubic foot would spend less than 23 milliseconds exposed to the flame.

TTFN

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[MechEngNCPE]

2640 CFM is a volumetric flow rate, and cannot be measured in miles per hour. I guess you mean Feet Per Minute?? There would be VERY little temperature rise in the scenario you are talking about.

 

[MintJulep]

BTU is a unit of energy. You need a unit of power.

At any rate the effect of a smallish flame, 100 feet away from an unknown quantity of an unknown material outside on a windy day will be approximately nothing.

 

[MechEngNCPE]

He means BTU/h but anyways...

 

[IRstuff]

The OP gave both: 2640cfm/30mph =1 ft², so 1 ft³ will be exposed to the heat source for 23ms.

23ms*3000 BTU/hr = 20.2 J

Specific heat of air = 1005 J/kg-K

density of air at 25C = 1.18 kg/m²

A bit more algebra results in 0.6°C temperature assuming blah, blah, and blah...

This is not at all surprising, is it? a 3000 BTU/hr burner is like a stove top set to medium flame. You can barely perceive the infrared thrown off by large gas patio heaters from more than about 10 ft away.

I've completely ignored the obvious fact that the heated air is more buoyant and more energetic, so it's highly unlikely that something that remote would see even 1/10 of the temperature rise calculated.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[BronYrAur]

I think we are missing the big picture. If your material is 100' away from the flame in a wide-open ambient environment, I don't see the flame affecting the material at all.

 

[ChasBean1]

IRStuff, wha? You got the right answer but I’d have to think as to why…

It’s simple. Add 3000 Btu/hr to 2640 cfm:

Q = 1.08 * cfm * dT, Q is in Btu/hr and dT is in °F
Q = 1.08 * cfm * (T2 – T1)
T2 = (Q / (1.08 * cfm)) + T1
T2 = (3000 / (1.08 * 2640)) + 100
T2 = 101°F

You have a 1°F (or a 0.6°C) rise.

 

[IRstuff]

CB,

You're right, I did it a roundabout...

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize