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re: my garage sweats
30 may 2005
longshot wrote:
>...what's the temperature of "dewpoint" ?
dew collects on grass when the grass temperature is less than
the dewpoint temperature of the air near the grass (which
increases with increasing humidity.)
condensation appears on a tool in a garage when the tool temp
is less than the dewpoint of the garage air near the tool.
if you stir a glass of water with an ice cube with a thermometer,
it reads the dewpoint temp of the ambient air when condensation
(dew) first appears on the outside of the glass.
td = ta/(1-taln(r)/9621), approximately, with temperatures in absolute
rankine degrees and rh r in fractional form. for instance, 70 f (ta
= 70+460 = 530 r) air at 50% rh (r = 0.5) has td = 530/(1-530ln(0.5)/9621)
= 510.5 r, ie td = 510.5-460 = 50.5 f.
nick
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