The Diffusion Model and Dispersion in a Straight Tube

The concentration profile formed from the originally homogeneous sample plug is the result of the combined convective and diffusion effects, the relative influence of which can be described by the convective-diffusion equation  

These results are, however, useful for future FIA work since  

They reveal the difficulty of reconciliation the theory with an experiment. 

The work of Vanderslice et al. [142] shows that FIA systems can be used for measurement of diffusion coefficients—provided that the flow geometry of the FIA system is kept constant (preferrably a straight rigid inner polished tube) and calibration can be made by means of a solute with known Dm value. 

It is well known that Taylor s treatment of axial dispersion is valid only when differences between axial dispersion and molecular diffusion Dm are small due to the choice of experimental conditions (i.e., when R is small, t is long, and F is very low). It follows from Taylor s work that the radial diffusion will start to affect the velocity profiles if 

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