Density ratio, porous media

R = retardation factor. The retardation factor is the ratio of the solution velocity to the radioelement velocity in a system of solution flow through a porous medium. The retardation factor R = 1 + Kd (p/) where p is bulk density of Hanford sediment (=1.65 g/cm3) and is the fraction of void volume in the sediment (=0.38). 

The quantity (ka/pfCPf) is termed the apparent thermal diffusivity and will here be given the symbol aa. It is not the thermal diffusivity of the fluid since it is the ratio of the apparent conductivity of the porous medium to the product of the density and specific heat at constant pressure of the fluid. 

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