Porous media area averaged velocity

By definition, with the area-averaged velocity defined as above, the continuity equation for flow in a porous medium w ill have the same form as that for the flow of a pure fluid, i.e., the continuity equation for flow through a porous medium is, if density variations are negligible ... 

The control parameters for the experiment described in Figure 15.6 are the mass of particles per unit surface, Mp / S, the area-averaged empty-bed velocity of the fluid in the column, U = Q/S, the density ps of the particles, and the density pf of the fluid. The diameter/) of the particles, as will be seen in section 15.6.3, chiefly influences the fluid flow in a porous medium, jointly determining with the kinematic viscosity v of the fluid the minimum fluidization velocity U f and the terminal entrainment velocity Ut, between which a steady-state fluidization regime is obtained. Furthermore, for a given velocity U of the fluid, the thickness of the fluidized bed increases if the diameter of the particles decreases, for the same mass of particles in the colunrn. 

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