Thermo-physical characterisation of natural rocks and impact analysis of variations in their thermo-physical properties on thermal storage performance

In this study, the thermal characterisation of natural rock samples from Zimbabwe for low-temperature industrial thermal energy storage (TES) applications was carried out. Thermal stability, specific heat capacity, thermal diffusivity, thermal conductivity and density were determined. Variations in these parameters were evaluated and their impact on thermal storage performance was analysed. Basalt and dolerite samples from different locations were found to have average specific heat capacities of 826 and 853 J/kg K, respectively, at room temperature. Insignificant variations were observed with differences of 3.4% for basalt and 1.7% for dolerite samples. Also, negligible differences of 0.3% and 0.7% in densities for rocks of the same type but of different origins were obtained for basalt and dolerite samples, respectively. However, significant variations in thermal diffusivity of all the igneous and metamorphic samples were observed with quartzite rock exhibiting the highest value of 2.1 x 10-6 m2/s, while the values for the other samples range from 0.9 x 10-6 to 1.6 x 10-6 m2/s. This implies that the thermal efficiency of sensible TES systems that use different or the same rock types from different locations can be significantly high to be overlooked. Thermo-gravimetric analysis results revealed that the rock samples studied have good thermal stability for low-temperature heat storage applications.