Drying Flashcards
involves the removal of moisture, usually water, from a solid by allowing the
composite material to come into contact with a drying medium that supplies the heat needed by the moisture to evaporate
Drying
can be obtained from the rate of drying
drying time
X refers to the
free moisture
X* refers to the
equilibrium moisture content
moisture that cannot be evaporated and dependent (very much) on the nature of solid and condition of the drying medium
X* - equilibrium moisture content
may be determined based on the conditions (temperature, humidity and velocity) of the drying medium subjecting the solid material.
drying time
The drying conditions may be constant which is typical
for
batch dryers
The drying conditions may be variable which usually occurs for
continuous dryers operating under
low temperature drying.
graph that uses to determine the drying time
drying rate vs moisture content
The moisture removed is unbound moisture
constant rate period
constant rate period is unbound moisture where it is capable of generating a partial pressure equivalent to the ______________ at the surface of the solid
vapor pressure
The moisture involved is referred bound moisture
falling rate period
falling rate period involves bounded moisture where the water has to travel to the surface by _______________________ or both in order to evaporate
capillary action or by diffusion
may be evaluated for direct driers by applying simultaneously the mass and heat transfer equations
constant rate of drying
in drying, if radiation and conduction is neglected, the surface tempt of solid can be taken as equivalent to
wet bulb temperature
