The thermal conductivity of powder beds. A model, some measurements on UO2 vibro-compacted microsperes, and their correlation

An analytical model to describe the thermal conductivity of unsintered packed powders is developed. This is based on one due to Deissler and Eian, but extended to include low gas pressures, when the powder bed conductivity is a function of pressure, and also high temperatures, when radiation between adjacent particles becomes a significant heat transfer mechanism. Some thermal conductivity measurements of vibro-packed microspheres of uranium dioxide are reported. Four different powder beds, comprising various combinations of 35, 300 and 1200 μm diameter microspheres, were measured in helium, nitrogen and krypton at pressures up to 0.6 MPa over the temperature range 370-1170 K. Satisfactory agreement between these experimental results and the model was obtained. A method of calculating temperature jump distance values from powder bed conductivity measurements is developed. Figures obtained using the present experimental results are in accord with published data, which were derived using other experimental techniques. (orig.)