Thermal conductivity of coal ash and slags and models used

A one-dimensional heat transfer method was used to determine the thermal co nductivity for a range of coal ash and synthetic ash samples at elevated te mperatures. The effect of parameters such as temperature, porosity, and sin tering time were investigated, The thermal conductivity of the samples was generally observed to increase with increasing temperature. During heating of the samples, softening of minerals and sintering reactions resulted in c hanges in the physical structure of the ash, which then altered the observe d thermal conductivity. The thermal conductivity of sintered ash samples wa s found to be higher than that of unsintered samples. The sintering tempera ture and sintering time were found to increase the observed thermal conduct ivity irreversibly. A decrease in sample porosity was also observed to incr ease the thermal conductivity, Chemical composition was found to have littl e effect on the thermal conductivity, apart from influencing the extent of sintering. Predictions of the thermal conductivity of ash samples based on Rayleigh's model are also presented. The thermal conductivity of slag and particulate structures was modelled by considering spherical pores distributed in a con tinuous slag phase. A particulate layer structure was modelled by consideri ng solid particles dispersed in a continuous gas phase. The Brailsford and Major model of random distribution for mixed phases gives results within 20 % of the measured values for a partially sintered sample. (C) 2000 Elsevier Science Ltd. All rights reserved.