Mass Transfer
The drying time between fixed moisture content within diffusion controlled 'falling rate period' is proportional to (assuming that drying occurs from all surfaces of the solid) (where, T = thickness of the solid )

T
√T

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

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

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