Non-steady state diffusional flow

Equation (1.61) was applied by Barter and Grove [49] with the assumption that l i = V2 to obtain  

Ross and Girafalco assumed no tortuousity factor on the grounds that the internal pore structure is already accounted for and obtained a similar equation to (1.63) with a constant of 144/13. This value was also adopted by Krishnamoorthy etal. [50,51]. 

This procedure has been used for surface area determination and generates values smaller than those found by gas adsorption. It is difficult to determine accurately, however, and the technique is not recommended for routine analyses. 

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