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re: equation for "grains of moisture"
13 feb 2002
joe geluso wrote:
>>t (f) air at r% rh has vapor pressure pa = r/100exp(-17.863-9621/(460+t))
oops. sorry. that should be +17.863.
>>"hg, and the humidity ratio w = 0.62198/(29.921/pa-1) pounds of water per
>>pound of dry air, and there are 7,000 grains per pound. the density of 70 f
>>air is 0.075 lb/ft^2.
>
>i tried this in a quattro spreadsheet with the following formula in
>the cell labeled "pa":
>
> +r/100*@exp(-17.863-9621/(460+t))
>
>the value in the cell labeled "r" is 50
>the value in the cell labeled "t" is 70
so pa = 0.5exp(17.863-9621/(460+70)) = 0.374 "hg,
and w = 0.62198/(29.921/0.374-1) = 0.00788 and we have
7000x0.00788 = 55 grains of water vapor per pound of dry air...
nick
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