New equations for porous media mass and momentum conservation for variable fluid and porous media properties are derived by representative volume averaging of the microscopic laws. The new mass conservation equation contains an extra term interpreted as mass transfer by spatial dispersion in porous media. The new momentum conservation equation contains only one empirical parameter, referred to as an apparent permeability. It is shown that the Klinkenberg and Forchheimer equations can be derived readily from the apparent permeability concept. Therefore, it is concluded that future research should be devoted to developing correlations for the apparent permeability rather than an absolute permeability, inertia resistance coefficient, and other parameters that the special equations Darcy, Forchheimer, and others may include. It is also shown that apparent permeability is a function of the porous media Reynolds number which implicitly includes the information about the fluid conditions through density, viscosity, and flow rate, and the information about the porous media properties through the use of an apparent pore size diameter concept. The present study, thus, leads to new insights into the mathematical description of the flow behavior in porous media.

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