Two of the main equations used to estimate the permeability in refractory castables are analyzed in this paper. The predictability of Darcy and Forchheimer equations is compared through examples involving gas, liquid and molten metal flow situations. It can be observed that Darcy equation disregards density effects on the fluid pressure drop. As a consequence, the fitted curve is only useful within the fitting range and the curve extrapolation might not be valid for other fluids or other flow situations. Forchheimer equation, on the other hand, yields reliable parameters in any flow condition. It is also demonstrated that the compressibility effect should be considered when permeability tests are carried out with gas flow. Deviation between experimental data and fittings are more significant at high fluid velocities and with low-porosity structures.
Refractory castables; permeability; performance
