80-6 Environmental
80.1.4 Psychrometer
Two thermometers are ventilated with the gas of unknown humidity. One sensor, the dry bulb, mea-
sures
th
e
ga
s
te
mperature
t. e ot
her
se
nsor,
th
e
we
t
bu
lb,
is su
rrounded
by a wi
ck
sa
turated
wi
th
pu
re
wa
ter
. e en
ergy
re
quired
to ev
aporate
wa
ter
in
to
th
e
ai
r
st
ream
co
ols
th
e
we
t
bu
lb
to a te
mperature
t
w
.
e v
apor
p
ressure
e i
n
t
he
s
ampled
g
as
i
s
c
alculated
w
ith
t
he
p
sychrometer
e
quation:
e e A P t t= − ⋅ −
w w
( )
(80.2)
where
e
w
is the saturated vapor pressure at temperature t
w
P is the total atmospheric pressure
A
i
s
t
he
p
sychrometer
c
oecient
A
de
pends
on ve
ntilation
sp
eed,
di
mensions
of th
e
we
t
bu
lb,
an
d
ra
diative
he
at
ex
change
be
tween
bo
th
dr
y
an
d
we
t
bu
lbs
an
d
th
eir
su
rroundings
. e at
tractiveness
of ...