CHAPTER IV
MEASURING THERMAL DIFFUSIVITY OF SOILS
Introduction
The temperature distribution of heat within a body is governed by
Fourier's law of conduction. For a one-dimensional body with no heat
generation, the partial differential equation describing the transient
temperature response subjected to various boundary conditions is
(Equation 4-1)
aT a2T
t = Dt -a (4-1)
az
The thermal diffusivity (Dt) is the property of a material which
determines the rate at which heat is propagated. The thermal
diffusivity is defined as the ratio of the thermal conductivity to the
volumetric heat capacitance (Equation 4-2).
Dt = C (4-2)
A composite material such as soil may have thermal properties which
vary with space and time due variation of the composition with time and
space. The factors affecting the thermal diffusivity of the soil are
1. soil type,
2. soil water content,
3. soil bulk density and
4. possibly soil temperature.