Environmental Engineering Reference
In-Depth Information
TABLE 7.1
Air.Density-Temperature.Relationship
EffectofTemperature
Acoustic
Impedance
Z in N·s·m
−3
Temperature
ϑ
in °C
SpeedofSound
c in m·s−1
DensityofAir
ρ
in kg·m
−3
+35
351.96
1.1455
403.2
+30
349.08
1.1644
406.5
+25
346.18
1.1839
409.4
+20
343.26
1.2041
413.3
+15
340.31
1.2250
416.9
+10
337.33
1.2466
420.5
+5
334.33
1.2690
424.3
±0
331.30
1.2920
428.0
-5
328.24
1.3163
432.1
-10
325.16
1.3413
436.1
-15
322.04
1.3673
440.3
-20
318.89
1.3943
444.6
-25
315.72
1.4224
449.1
Using.this.method,.error.in.the.density.calculation.is.less.than.0.2.percent.in.
the.range.of.−10°C.to:
p
p
d
v
ρ
humid air
=
+
.
.
(7.12)
R
T
R
T
i
i
d
v
where:.50°C..The.density.of.humid.air.is.found.by:
ρ.. =.Density.of.the.humid.air.(kg/m³);
p
d
=.Partial.pressure.of.dry.air.(Pa);
R
d
..=.Speciic.gas.constant.for.dry.air,.287.058.J/(kg·K);
T
.. =.Temperature.(K);
p
v
..=.Pressure.of.water.vapor.(Pa);
R
v
..=.Speciic.gas.constant.for.water.vapor,.461.495.J/(kg·K).
The.vapor.pressure.of.water.may.be.calculated.from.the.saturation.vapor.
pressure.and.relative.humidity..It.is.found.by:
.
v
= φ
i
sat
.
(7.13)
p
p
where:
p
v
.=. Vapor.pressure.of.water;
ϕ.=.
Relative.humidity;
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