MECH 3020 Thermodynamics II: Homework set #11, Due 03/11
The solutions are worked out symbolically.
1. Current outside conditions are 19
◦
C, 43% relative hu
midity. Calculate:
(a) The dew point temperature. 6.5
◦
C
(b) The speciﬁc humidity
ω
. 0.006
(c) The speciﬁc volume of the mixture
per kg of dry
air
. 0.835
2. A 1 m
3
volume of atmospheric air is at 1 atm, 25
◦
C,
and 60% relative humidity. Calculate
(a) The partial pressures of the water vapor and the
dry air.
P
v
=
ϕP
sat
(25
◦
C),
P
a
=
P

P
v
(b) The masses of dry air and water.
m
a
=
P
a
V/R
a
T
,
m
v
=
P
v
V/R
w
T
3. The system in problem 2 is now cooled at constant pres
sure to a temperature of 5
◦
C. Calculate
(a) The volume of the system at the point, during the
process, at which water begins to condense into
the liquid phase. Find the dewpoint temperature
T
dp
, and
V
dp
=
V
1
(
T
dp
/T
1
), since total pressure is
constant and the gases are ideal. Use Kelvin.
(b) The total mass of liquid water that condensed dur
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 Spring '11
 MACKOWSKI
 Water vapor, Psychrometrics

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