Superficial volume-average velocity, defined

For a concentrated binary electrolyte, the superficial volume-average velocity v is defined as... 

The spin-displacement density function, c (z, Z), and the normalized displacement distribution function, P(z, Z), can be converted readily into the joint spin-velocity density function, q(z, vn), and the normalized velocity distribution function, P(z, vn), respectively, with the net velocity vn defined as vn = Z/A. Once the velocity density function is determined for each of the volume elements, the superficial average velocity, v, is calculated by [23] ... 

Here, the superficial velocity, v, represents a fluid state, and the density, p, a fluid property which, for a compressible fluid, can be related to the pressure through an equation of state. The porosity, (p, which is defined as the void fraction within the media, is a macroscopic property of the porous material. Sources and/or sinks located within the physical system are represented using y/. Volume averaging the differential momentum balance for the same physical situation yields Darcy s law ... 

Mobile phase velocity. Chromatographers define the cross-section average velocity of the mobile phase as the ratio, u = L/fo, of the column length and the hold-up time or retention of a nonretained compoimd. This time should be corrected for the transit time through the extracolumn volumes between injection valve and column inlet and between column inlet and detector. Chemical engineers tend to prefer the superficial velocity, or ratio of the flow rate and the column cross-section area, wq = Fv/S. Obviously, we have ... 

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