Basic Principles of Elutriation

Theoretical difficulties associated with the performance of a vertical elutriation are  

The fluid flow velocity across the cross section of the elutriating chamber is not constant. Thus in a cylindrical chamber the distribution is parabolic (see discussion of fluid flow in reference 1). Random fluctuations in fluid flow cause migration of larger fineparticles just supported by the higher flow in the center regions 

If an elutriator is operated for long periods of time, the cut size associated with maximum flow along the center of the elutriator column dominates the fractionation achieved with the elutriator rather than the cut size calculated from the average flow. 

To obtain steady flow conditions, relatively long feed pipes to the elutriator are necessary. If there are any sharp bends in the feed pipework leading to or from the main tube, flow conditions are hard to predict and fractionation performance has 

A practical problem associated with the operation of the elutriator is that the solids concentration of the suspension affects the performance of the elutriator usually the higher the concentration of solids, the less predictable the fractionation efficiency. If the fluid flow rates required to fractionate the powders are very low, requiring several days to achieve the required fractionation, it is difficult to achieve thermal isolation and stability of the system. It is also difficult to generate, maintain, and monitor the low flow rates required to operate the system. 

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