Single- and Dual-Probe Heat Pulse Probe for Determining Thermal Properties of Dry Soils

Heat pulse methods include the dual-probe (DP) and single-probe (SP) methods. The DP method is a widely used method for determining the thermal conductivity (K) and thermal diffusivity (β) 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 the thermal properties of air-dried soils. The thermal properties of three sands were measured using differential scanning calorimetry (DSC) and the DP and SP methods. For the SP method, the small-time and large-time solutions of the perfect conductor model and hollow cylindrical probe model were fitted to the respective small-time and large-time temperature vs. time curves. Both K and β of the soil were determined by the SP method. The DP and SP methods yielded similar K values for the three air-dried soils with a relative deviation <6.1%. In comparison with the DSC measurements, the DP method overestimated the specific heat (c) by 19 to 29%, while the SP method with the hollow cylindrical probe model underestimated c by 21 to 8%, and the SP method with the perfect conductor model resulted in −4 to 7% error. Therefore, the SP method with the perfect conductor model gave the most accurate estimate of c.