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Formula for Natural Convection in Calm Air2

Formula for Natural Convection in Calm Air

(OP)
From Chopey (2nd and 3rd edition) I have this formula (reproduced on this web page in part two of the calculation procedure).

I'm trying to find an equivalent formula in a reference text (started with McCabe Smith & Harriott) but I can't find any support. My problem is knowing where the coefficient 0.27 came from. Is it dependent on the carbon steel pipe? Or some other property? I need to know if this formula can be applied to any situation, regardless of the piping material or whatever "air" is (maybe a pipe in a nitrogen environment or something, who knows?)

Thanks! I'm looking in Perry's now... Hopefully someone can direct me to the source of that linked equation?

Q/A = (0.27 dT^1.25)/D^0.25

Thanks!

RE: Formula for Natural Convection in Calm Air

It looks to be a deconstruction of the standard natural convection equation. The 0.27 is usually the multiplier of the Rayleigh term to get the Nusselt number.

TTFN (ta ta for now)
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RE: Formula for Natural Convection in Calm Air

The detailed expression is derived from a combination of the fluid's Grashof and Prandtl numbers - see the subsection on natural convection in the chapter on Heat and Mass Transfer in Perry.

RE: Formula for Natural Convection in Calm Air

Equivalent formulas in a reference text can be found in Heat Transfer in Process Engineering by Eduardo Cao. It has simplified equations for different objects,

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