Simultaneous Estimates of Thermal Conductivity, Heat Capacity and Contact Resistance with the Heat Pulse Probe.

Heat pulse techniques are routinely used to determine soil and other media’s thermal properties. Due to the approximations adopted in current modeling, only thermal conductivity (k) is obtained with the single needle (SN) probe, while dual needle (DN) probes yield both k and the sample’s specific heat capacity (c). In both cases, errors can be very large due to the additional contact resistance resulting from small air gaps between the needles and the sample. This effort shows that both k and c can be successfully determined with the SN probe, which presents clear practical advantages compared to the DN probe. The analysis relies on a more accurate description of the probe’s temperature response, which accounts for the finite thermal conductivity and heat capacity of the metal needle. Moreover, the actual heat pulse’s shape is estimated through proper calibration. The sample’s thermal properties are obtained through inverse analysis of the temperature signal. This is reduced to an ordinary regression problem, which we solved through a suitably designed Artificial Neural Networks (ANN). This technique yields very accurate estimates of both thermal properties over a wide range. Most importantly, the accuracy is unaffected by the presence of the contact resistance, which is also allowed to vary over a wide range. A comprehensive series of experimental results confirms the validity of the proposed method.