Thermal Conductivity: IX, Experimental Investigation of Effect of Porosity on Thermal Conductivity

The effect of isometric approximately spherical pores and anisometric cylindrical pores on the thermal conductivity of alumina, graphite, and nickel has been investigated. Pore orientation is found to affect profoundly the thermal conductivity for a given porosity. At temperatures below about 500°C. the conductivity of a porous sample in any given direction is equal to the solid conductivity times one minus the cross‐sectional pore fraction or k p = k s (1 − P c ). At higher temperatures the pore size and emissivity become important.