Free moisture content X is the difference between given moisture content of

# Free moisture content x is the difference between

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Free moisture content (X) is the difference between given moisture content of solid (X t ) and EMC, equilibrium moisture content (X*) This excess moisture can be removed by drying under the given percent relative humidity Free Moisture of Substance

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SILK @ 50% H R EMC (X*) = 8.5 kg H 2 O/ 100 kg dry material when in contact with air of 50% H R , 25◦C. If a wet solid (Silk) contains (X t ) 10 kg H 2 O/100 kg dry material, therefore only (X) 1.5 kg H 2 O/100 kg dry material can be removed (X - free moisture) Free Moisture of Substance 50 8.5
Wet and Dry Basis To be dried from a free moisture content X 1 = 0.38 kg H 2 O/kg dry solid to X 2 = 0.25 kg H 2 O/kg dry solid. To be dried from a free moisture content of 38% to 25%, on a wet basis.

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Overall drying process can be divided in three parts: Material starts to be heated from initial temperature. Moisture starts to evaporate from the surface. Concentration of water decreases. 1. Warm-up Period 2. Constant Rate of Drying Period 3. Falling Rate of Drying Period The surface of the material dries up. The drying rate starts to decrease. At this point, temperature of the material will be constant, i.e. the heat from the air is consumed by evaporation of the free moisture/water. Drying rate will be constant. 1 (A – B, A’ – B) 2 (B – C) 3 (C – E) Drying Curve Free moisture content vs Drying time hot cold
Rate of Drying dX dt

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Rate of Drying Critical moisture content (Drying rate starts to 1 (A – B, A’ – B) 2 (B – C) 3 (C – E) Free moisture content vs Drying time Drying rate vs Free moisture content hot cold dX dt
Calculation Method for Constant Rate Drying Period R c

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Calculation Method for Falling Rate Drying Period
Calculation Method for Special Cases in Falling Rate

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