Drying the wet solids with a gas which is at a fixed temperature and humidity it will show a behavior as follows:
Immediately after contact between the solids with the media conditioning, the temperature of the solid material will conform to happen steady state. The temperature of the solid material and the drying rate will rise or fall reaches steady state. In this condition the wet-bulb temperature of the media dryers, and consequently the temperature of the solid material will also be the same as the wet-bulb temperature of the gas. But this conclusion is not appropriate because there is no heat and mass transfer. When the temperature reaches the wet bulb temperature of the gas, it will get a sufficient condition is stable, and the drying rate will also be constant. This condition is called the drying period at a constant rate, or so-called constant rate drying period.
That period will end if the solid material reaches a critical water content (critical moisture content). Above this point the surface temperature rises and the drying rate will go down quickly. Period with the rate of decline (falling- rate period) will last longer than the drying rate constant (rate constan period) although the water will evaporate less.
The drying rate will reach zero at some equilibrium moisture content (equilibrium moisture content) which is the lowest moisture content obtained with this solid material in the drying process conditions that do.
Source :
Geankoplis, C. J., 1993, � Transport Process and Unit Operations �, 3rd ed., pp.524-526, 531, Allyn and Bacon, Inc, London
KEYWORDS :
read more : Drying/ Pengeringan
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