Dual probe methods for determining soil thermal properties: numerical and laboratory study

Abstract

Dual-proije methods which implement analytical solutions of the conduction heat transfer equation provide a means to simultaneously determine volumetric heat capacity, thermal conductivity and thermal diffusivity of soil. Thermal properties are determined from temperature monitored by a sensing probe over time at a known distance from a line heatsource. This study applies the dual-probe method to aqueous a-alumina colloidal suspensions and aqueous solutions of glycerol 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 using the known or independently determined thermal properties. The thermal properties were also estimated using nonlinear least-squares curve fitting. Relative error of the estimated heat capacity and thermal conductivity was less than 2 percent and 6 percent, respectively. Signal noise cim be a problem in cases when the maximum temperature increase at the sensing probe is less than 0.5 °C. Good agreement was found when dual-probe temperature measurements performed on a saturated sand were compared with estimated temperature using curve fitted properties and using a mechanistic model. INTRODUCTION Soil is an agglomeration of constituents of various forms which are conjoined by mass and energy balances. An understanding of this dynamic system is dependent upon the ability to discern the properties used to describe the fundamental relationships which govem the balances. Though much progress has occurred in recent years, techniques which allow scientists and engineers to confidently quantify soil properties in a direct or indirect fashion are deficient for many of the soil properties. These deficiencies persist as constraints toward our understanding of soil systems. The determination of soil thermal properties is one such area that needs improved measurement techniques. A description of the thermal regime is necessary to evaluate