Mass Transfer
Channelling is most severe

At very high liquid flow rate
In towers packed randomly with crushed solids
In dumped packing of regular units
In towers packed with stacked packing

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Mass Transfer
When the solvent dissolves very little of solute, then

Solvent of low latent heat of vaporisation should be used
Very small quantity of solvent is required
Large quantity of solvent is required to extract the solute
Solvent of low freezing point should be used

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