Environmental Engineering Reference
In-Depth Information
Table 2.9 Thermal Properties of Air at Various
Temperatures
.......
Table 2.10 Viscosity of Air at 101.3 kPa
Absolute (dynamic)
Temperature (
◦
C)
10
−
5
s/m
2
)
Specific Heat
Viscosity,
ν(
×
·
N
Temperature,
Capacity,
Thermal Conductivity,
T
(
◦
C)
C
a
(kJ/kg K)
λ
a
(W/m K)
−
10
1.667
0
1.705
−
50
1.005
0.0204
10
1.761
0
1.005
0.0243
20
1.785
20
1.005
0.0257
30
1.864
40
1.005
0.0271
40
1.909
60
1.009
0.0285
80
1.009
0.0299
Source:
Modified from Tuma, 1976.
100
1.009
0.0314
Most properties of the contractile skin appear to be different
from those of the contiguous water phase (Davies and Rideal,
1963). For example, the density of water in the contractile skin
is reduced, its heat conductance is increased, and its birefrin-
gence data (i.e., a measure of the water structure) are similar
to those of ice. The transition from liquid water to the con-
tractile skin appears to be distinct and jumpwise according to
Derjaguin (1965). It is interesting to note that insects such as
the “water spider” are able to walk on top of the contractile
skin, while insects such as the “backswimmer” are able to
walk on the bottom of the contractile skin (Milne and Milne,
1978). The water strider would sink into the water were it not
for the contractile skin, whereas the backswimmer would pop
out of the water if the contractile skin did not exist.
Source:
www.vaisala.com.
2.3.3.6 Viscosity of Air
The viscosity of air at atmospheric pressure (i.e., 101.3 kPa)
and different temperatures is given in Table 2.10.
Figure 2.34 shows a comparison of the absolute viscosities
of air, water, and other materials at different temperatures.
The viscosity of air increases as the temperature increases.
2.3.4 Air-Water Interface or Contractile Skin
The most distinctive property of the contractile skin is its abil-
ity to exert a tensile pull. It behaves as if it is an elastic mem-
brane under tension interwoven throughout the soil structure.
10
−
2
1
×
6
4
Brine, 20% NaCl
2
Mercury
1
×
10
−
3
6
4
Water
2
1
×
10
−
4
6
4
Air
2
10
−
5
1
×
20
0
20
40
60
80
100
120
−
Temperature,
°
C
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