Diffusion effects irregularly shaped particles

X depends on the irregularity of the particles (particle shape) and on the column material (steel gives more disturbance than glass) the relative effect will always increase as the column diameter decreases. The above-mentioned effects have led to an optimum internal diameter of 2-5 mm for LC columns. In a column with this internal diameter, which is uniformly packed with small spherical particles, the eddy diffusion will be limited. The X value is about 1 for spherical particles. 

For irregular particles produced by crushing or grinding, the external surface is larger than for spheres of the same nominal size, which tends to increase the effectiveness factor but also increases the pressure drop through a bed of particles. Shape factors based on pressure drop are given for some typical granular solids [23], but these shape factors are not used for pore diffusion calculations, and R in the Thiele modulus is taken as 0.5 times the nominal or screen size. 

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