135
DeVries (1975) presented methods for calculating the thermal
properties of the soil based upon the various volume fractions of the
solid, liquid and air constituents of the soil. These equations
estimated the specific heat and thermal conductivity of various soils.
However, extensive tests for a range of soil types as well as moisture
contents and density have not been conducted. The DeVries method has
been shown to estimate the thermal properties within ten percent for
limited soils. Tollner et al. (1984) compared the experimental values
of the thermal conductivity for potting soils consisting of various
mixtures of sand and pine bark to those calculated. They achieved an
average deviation between experimental values and values calculated by
the DeVries method of approximately fifteen to twenty percent.
Objectives
The objectives of this study were to determine a method by which
the thermal diffusivity of the soil could be obtained and to compare
the measured data with that calculated by the DeVries method. A third
objective was to determine a technique by which the measured data could
be used in a simulation of the energy transfer within the soil.
Literature Review
Methods of determining the thermal conductivity or diffusivity of
a material are based upon measuring either the steady-state or
transient temperature response to a particular set of initial and
boundary conditions. Steady-state or equilibrium methods are based
upon Fourier's law of conduction for a one-dimensional homogeneous,
isotropic material (Equation 4-3).
q (43)
q = X -- (4-3)