Assessment of Forchheimer's equation to predict the permeability of ceramic foams

Correct estimation of the pressure drop in filtration processes that involv e fluid velocity variations is of major importance, because it allows the f iltration rate and/or the energy consumed on fluid flow to be more accurate ly controlled. Permeability of porous filters has been often described by F orchheimer's equation, which establishes a nonlinear dependence between pre ssure drop and fluid velocity. Two constants, k(1) and k(2), dependent only on the medium, quantify the viscous and inertial effects on the pressure d rop curve. In this work, experimental data of airflow through 10 pores per linear inch ceramic foam filters are used to show that a single sample may have completely distinct permeability constants depending on the data range chosen for analysis. The Darcian permeability constant k(1) displays highe r variation than the non-Darcian permeability constant k(2). The conclusion is that special attention must be taken to represent permeability of highl y porous structures in a large velocity range. The predictability of Forchh eimer's equation generally worsens when less data are included in the curve fitting, particularly at low velocities. Careful consideration should be m ade if constants k(1) and k(2) are intended to be used for permeability est imation beyond the fitting range.