32
For the purposes of simulation, the barometric pressure (p) was assumed
to equal the standard pressure (p0). The diffusivity then became a
function of time and space due to the temporal and spatial variation of
the soil temperature. Diffusivity was determined throughout the soil
profile by substitution of the soil temperature in equation (2-34).
Thermal properties
Very little literature exists regarding measurement of the thermal
properties of the soil. Soil composition as well as density and water
content affects the thermal properties of the soil (Baver, 1972). The
thermal diffusivity is the ratio of thermal conductivity to the product
of soil density and specific heat. Density is a property which can be
obtained as a function of depth at a given location by core samples.
Vries (1975) describes a method by which the volumetric heat
capacitance and the thermal conductivity of the soil can be calculated
based upon the volume fractions of the various soil constituents.
The volumetric heat capacitance is defined as the product of the soil
density and the specific heat and can be calculated from:
Cs xqcq + xCm + xoCo + xwCw + xaCa f2'36)
where
C
S
volumetric heat capacity [J-m'3*0^1]
X
=
volume fraction [m3*m~3]
q
=
quartz
m
s
mineral
0
=
organic