A methodology for determining thermal properties of rocks

Abstract

The migration of heat in porous media has attracted attention of the research fraternity, since almost a century. Studies conducted in the past reveal that heat migration in a medium primarily depends on its thermal resistivity (defined as the ability of the material to resist heat flow in it), its specific heat (defined as the ability of the material to store heat) and thermal diffusivity (which combines the transmission and storage properties of the material and is an indicative of the rate of change of temperature within the material). For safe and proper execution of various civil and electrical engineering projects, determination of thermal properties of soils such as thermal resistivity [1–22], thermal diffusivity [1,23] and specific heat [3,19] is quite essential. However, thermal properties of rocks would play an important role for extremely environmental sensitive projects such as disposal of high-level radioactive waste in deep underground disposal sites or repositories [24,25]. In this direction, attempts have been made wherein rock has been powdered to determine its thermal conductivity [26–28] or its chips have been used [29]. However, these studies would not yield accurate results, mainly, due to the lack of representative matrix of the rock mass [30]. Attempts have also been made by earlier researchers to determine thermal properties of rocks using divided bar method [31], the transient plane source, TPS-method [32], and different probe methods [33–34]. However, these methods are time consuming, expensive, and quite complicated in terms of instrumentation and insulation of the surfaces of the rock sample from the ambience. With this in view, an attempt has been made to develop a methodology, which can be employed to determine thermal properties of the rock samples easily and quickly. Details of the methodology are presented in this technical note and its validation has been demonstrated vis- a-vis results reported in the literature.