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re: air/wind convection coefficient
31 mar 1998
stephane wrote:
>if you know values or formula to compute wind convection coefficient on a flat
>plate (a small piece of terrain), could you please write them...
figure 1 on page 22.1 of the 1993 ashrae handbook of fundamentals has
some fairly linear-looking graphs of surface conductance in btu/h-f-ft^2
vs air velocity in mph for various 12 inch squares, from what looks like
1.5 + v/5 for smooth surfaces like glass to 2 + v/2 for rougher surfaces
like stucco. concrete is in between, with h = 2 btu/h-f-ft^2 at v = 0 mph
and 10 at v = 25 mph.
>i have my own formula which is a laminar or turbulent fluid flow over
>a flat plate
i wonder what that one is...
>and i have another one that i bumped into which is:
>h= max(5, 8.6*v^0.6/lc^0.4) v being the wind speed (m/s)
>and lc the characteristic length (m)
so that would make h = 61.2 w/m^2c, ie 10.8 btu/h-f-ft^2
for a 12" concrete square in a 25 mph wind...
nick
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