Mass Transfer
Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)

Decreases pressure drop, increases surface area
Increases pressure drop, increases surface area
Increases pressure drop, decreases surface area
Decreases pressure drop, decreases surface area

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Mass Transfer
Priming in a distillation column

Reduces the overall pressure drop
Is desirable from point efficiency consideration
Is characterised by the presence of foam throughout the space between trays
Results from very low gas velocity

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