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Drying, Khairunnisa Binti Mazlan A20ET0324 - Coggle Diagram
Drying
Theory
removal of relatively small amount of water or organic liquids
final processing step before packaging
Methods
Batch
Continous
Categories
Direct contact with heated air at atmospheric pressure
Vacuum drying
freeze drying
Equilibrium moisture content
• lowest moisture content obtainable at
equilibrium
• on dry basis (kg of water/ kg of moisture free solid)
• depends on structure of solid, temperature
& moisture content of gas
• varies greatly with type of material for
any given % relative humidity
• decreases with increase in temperature
• assumed constant for moderate
temperature ranges
Bound Water
• the minimum moisture a material can carry
• intersection of 100% humidity line in equillibrium water content vs relative humidity
Unbound water
• excess water held primarily in the voids of the solid
Free moisture content, X
• moisture above the equilibrium moisture content
• can be removed by drying
Constant rate of drying period
To determine the time required for drying from x1 to x2
Predicted mass & heat coeffcient
Experimental drying curve
Humidity & Humidity chart
Humidity,H - kg of water vapour in 1 kg of dry air
Saturation humidity, Hs
Percentage humidity, Hp
Percentage relative humidity, HR
Dry & Wet Bulb Temperature
Wet bulb
decreases in temperature below the dry-bulb temperature until the rate of heat transfer from the warmer air to the wick is just equal to the rate of heat transfer needed to provide for the evaporation of water from the wick into the air stream
Dry Bulb
the ordinary temperature you measure with a thermometer
Khairunnisa Binti Mazlan A20ET0324