Heat Flow in the Soil
TABLE 8.2. Thermal properties of typical soil materials.
Material
Soil minerals
Granite
Quartz
Glass
Organic matter
Water
Ice
Air (101 kPa)
Specific
Heat
(J g-I K-I)
0.87
0.82
0.80
0.84
1.92
4.18
2.1 + 0.0073T
1.01
- -
Thermal
Conductivity
(W m-I K-I)
2.5
3.0
8.8
0.8
0.25
0.56 + 0.0018T
2.22 - 0.01 1 T
0.024 + 0.00007T
Volumetric
heat capacity
(MJ m-3 K-I)
2.3 1
2.16
2.13
2.28
2.50
4.18
1.93 + .0067T
(1.3 - 0.0041T)
x
about 3.5 MJ m-3 K-'. The slope of all lines is the same and is determined by the heat capacity of water. The intercepts differ because of the
differences in solid fractions in the different soils.
Example 8.1. Find the volumetric heat capacity of loam soil with a
water content of 0.2 m
3 m-3 and a bulk density of 1.3 ~ g / m ~ .
Assume
the organic fraction is zero.
Solution. The mineral fraction is the ratio of the bulk density to the mineral density. The mineral density of soil, from Table 8.2, is 2.65 ~ g / m ~ ,
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Volume Fraction of Water
FIGURE 8.2. Volumetric heat capacity of organic and mineral soils. Differences
are mainly due to differences in soil bulk density.