Dispersion and Mass Transfer Parameters in Packed Beds

Dispersion and Mass Transfer Parameters in Packed Beds 

In packed beds, the main parameters of transport of adsorbates are the axial dispersion coefficient and the fluid-to-particle mass transfer coefficient. The other important parameter, the intraparticle diffusion coefficient, is not dependent on type of adsorption contactor and the treatment described in Chapter 4 can be applied. 

Axial dispersion contributes to the broadening of the adsorption front due to flow in the void spaces between particles. Similar to diffusion phenomena, dispersion effect in the bed is expressed in terms of the following dispersion model  

Usually Et is considered to consist of contribution of molecular diffusion and the dispersion caused by fluid flow. 

dispersion caused by mokcular diffusion Dispersion due to molecular diffusion in the interparticle void spaces is described by the void fraction of the bed, e, and the tortuosity of the diffusion path in the void space. Unlike the diffusion in porous particles reviewed in Chapter 4, the latter is considered close to unity for diffusion in packed beds. Then, 

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