Test of a dual-probe, heat-pulse method for determining thermal properties of porous materials

Dual-probe heat-pulse methods, which implement analytical solutions of the conduction heat transfer equation, provide a means to simultaneously determine volumetric heat capacity (rho c), thermal conductivity (lambda), and thermal diffusivity (kappa) of porous materials such as soil. Thermal properties are determined front temperature monitored by a sensing probe over time at a known distance from a line heat source. This study applies the dual-probe method to aqueous alpha-alumina colloidal suspensions, aqueous solutions of glycerol and saturated soil, which have known or independently determined thermal properties to validate the method. Good agreement was found between the measured temperature distribution and the temperature described by the infinite line-source analytical solution by using the known or independently determined thermal properties. The thermal properties of the materials were also estimated by nonlinear least-squares curve fitting. Relative error of the estimated rho c and lambda was less than 2% and 6%, respectively. Good agreement was also found when dual-probe temperature measurements obtained for a saturated soil were compared with estimated temperatures based upon properties estimated by de Vries theory. Thus, the dual-probe heat-pulse methods show good promise as a tool for determining thermal properties of soil and other porous materials.