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hemi_fan
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I am working on a problem involving heat transfer from a horizontal pipe in air. I am having trouble with it and not getting the solution I expect, and I think it is because of the convection component of the heat transfer. The general formula I am following for convection from a horizontal pipe is:
Q = h*A*(Tsurface-Tambient)
where:
h = convection heat transfer coefficient
A = pipe surface area
Tsurface = surface temperature of pipe
Tambient = air temperature around pipe
I am using the following formulas for calculating the heat transfer coefficient:
Natural Convection:
h = 1.32*((Tsurface-Tambient)/D)^0.25
Forced Convection:
h = C*Re^n*Pr^(1/3)*k/D
where:
Re = Reynolds number
Pr = Prandtl number
k = thermal conductivity of air
D = outside pipe diameter
C,n = constants dependent on Re (can't remember their name off-hand, see chart)
Reynolds Number C n
0.4-4 0.989 0.330
4-40 0.911 0.385
40-4,000 0.683 0.466
4,000-40,000 0.193 0.618
40,000-400,000 0.0266 0.805
Are these formulas appropriate (natural convection in particular as this was given to me by a colleague and I have no clue where he got it)? The forced convection is from a textbook (which I don't have at the moment), however the book did not specify the orientation of the pipe. If anyone could chime in, or maybe provide a link to a 'how-to' on calculating convection around pipes that would be great, thanks!
Q = h*A*(Tsurface-Tambient)
where:
h = convection heat transfer coefficient
A = pipe surface area
Tsurface = surface temperature of pipe
Tambient = air temperature around pipe
I am using the following formulas for calculating the heat transfer coefficient:
Natural Convection:
h = 1.32*((Tsurface-Tambient)/D)^0.25
Forced Convection:
h = C*Re^n*Pr^(1/3)*k/D
where:
Re = Reynolds number
Pr = Prandtl number
k = thermal conductivity of air
D = outside pipe diameter
C,n = constants dependent on Re (can't remember their name off-hand, see chart)
Reynolds Number C n
0.4-4 0.989 0.330
4-40 0.911 0.385
40-4,000 0.683 0.466
4,000-40,000 0.193 0.618
40,000-400,000 0.0266 0.805
Are these formulas appropriate (natural convection in particular as this was given to me by a colleague and I have no clue where he got it)? The forced convection is from a textbook (which I don't have at the moment), however the book did not specify the orientation of the pipe. If anyone could chime in, or maybe provide a link to a 'how-to' on calculating convection around pipes that would be great, thanks!
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