Previous measurements of the spectral emissivity of coal ashes are converted to total absorptivities and emissivities. Below the temperature at which ash sinters, the total absorptivity of an ash layer—which is necessary for the estimation of radiative transfer in furnaces—is shown to depend on both the source (flame) temperature and the ash temperature. Synthetic mixtures of the oxides Al2O3, SiO2, and Fe2O3 are shown to give the same trends as those for ashes of the same Fe2O3 content.

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