The prediction of the emissivity and thermal conductivity of powder beds

A simple model for estimating the emissivity of the surface of a powder bed by knowing only the bed porosity and its solid emissivity is presented. Estimates by the model are compared with experimental measurements for powder beds of alumina, silicon carbide. and iron. Agreement within the uncertainty of the measurements of +/-10% is obtained. A view factor that adopts the predicted emissivity of the powder beds into its term is suggested for the calculation of the conductivity by radiation. For the prediction of the thermal conductivity of the powder beds, the authors compared the existing models in literature. They rederived the Zehner-Schlunder equation ( 1970) and made some modifications to it. Comparison of predictions by this equation with 424 measured values shows the predictions to be accurate to within a +/-30% relative error.