Simultaneous Determination of Thermal Diffusivity and Heat Capacity of Dry Soils.

Hot needle (HN) methods include dual probe (DP) method and single probe (SP) method. The DP method is a widely-used method for determining thermal conductivity (K) and thermal diffusivity (α) of soil. The SP method has been traditionally used for measuring K only. The objective of this study was to examine if the SP method can be used to estimate thermal properties (K and α) of air-dried soils. Thermal properties of three sands were measured using differential scanning colorimeter (DSC), DP, and SP method. Eight second heating duration with heating strength between 92 W m^-1 < q^' < 102 W m^-1 was used for DP and 600-s heating duration with heat source strength between 3.6 W m^-1 < q^' < 4.97 W m^-1 was used for SP. By fitting the small-time and large-time solutions of Blackwell (1954) to the respective small-time and large-time temperature versus time curves, both K and α of soil were determined from the SP method. The DP and SP methods yielded similar K values for the three air-dried soils with a relative deviation less than 6.1%. However, DP over-estimated heat capacity (c) by 19 % to 29 % in comparison with the DSC measurements, while SP did by less than 7.3 %.