147
locating the thermocouple near the center of the sample. These
precautions were both taken during the tests. Gaffney et al. (1980)
also demonstrated that conduction error did not significantly affect
the slope of the time-temperature curve.
A second source of error could arise from the movement of water
within the sample. The enhancement of the thermal conductivity due to
vapor movement in the soil occurs in response to concentration
gradients due to gradients in temperature within the sample and can be
calculated by (DeVries, 1975)
Dv 17 3ps
\ = hfg R^T dl
(4-17)
The apparent thermal conductivity is the sum of the conductivity for
conduction and the conductivity due to vapor movement (DeVries, 1975).
The apparent thermal diffusivity would be calculated by dividing the
apparent conductivity by the heat capacitance of the soil. Therefore,
the contribution of the vapor flow to the thermal diffusivity would be
Dtv
(4-18)
The temperature used in the calculation of the diffusivity due to vapor
movement was the time average temperature at the center of the sample.
Regression analysis was used to attempt to find the least squares fit
of the data using dry bulk density, volumetric water content and the