Drying Flashcards
generally refers to the removal of liquid from a solid by evaporation
Drying
is a relative term and means merely that there is a reduction in moisture content from an initial value to some acceptable value.
Drying
involves the removal of water at temperature below the boiling point by circulating air or some other gas over the material.
Drying
usually refers to the final removal of water and the operation which often follows crystallization or filtration.
Drying
is used to pick up the vaporized liquid from the solids
air
drying properties of air is done by
heating it or lowering its humidity or both
expresses the moisture content of wet solid as mass per mass of bone-dry solids.
Dry - weight basis
expresses the moisture in a material as percentage of the weight of the wet solid.
Wet - weight basis
Drying proceeds by
diffusion of vapor from the saturated surface of the material across a stagnant air film into the environment.
The magnitude of the constant rate depends upon three factors:
- The heat or mass transfer coefficient
- The area exposed to the drying medium
- The difference in temperature or humidity between the gas stream and the wet surface of the solids
Falling rate period usually divides into two zones
- the zone of unsaturated surface drying (the first falling rate period – portion CE)
- the zone where internal moisture movement controls (the second falling rate period – portion DE)
It is the average moisture content when the constant rate period ends.
CRITICAL MOISTURE CONTENT (XC)
CRITICAL MOISTURE CONTENT (XC) value depends on:
- the rate of drying
- the thickness of the material
- the factors influencing moisture movement and resulting gradients within the solid
It is the limiting moisture to which a given material can be dried under specific conditions of temperature and humidity.
EQUILIBRIUM MOISTURE CONTENT
Equilibrium moisture content depends greatly on
the nature of the solid.
