Drying a wet solid from 50% moisture down to its critical moisture content of 15% requires 6 hours. Under identical drying conditions, how much additional time is needed to further reduce the moisture content to 10%, given an equilibrium moisture content of 5% ?
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Answer: C. 71 min
Explanation
Initial drying from fifty to fifteen percent moisture takes six hours during the constant rate period. Further moisture reduction from fifteen down to ten percent occurs within the falling rate period. Applying falling rate drying kinetics and integrating mass balances yields an additional time of 71 minutes. Critical moisture content marks the transition point between constant rate and falling rate drying periods. Equilibrium moisture content represents the lowest bound moisture a solid can attain under ambient conditions. Falling rate drying calculations require integrating equations that account for internal moisture diffusion resistance.
Accurate drying time estimation prevents thermal degradation of heat-sensitive materials in industrial kilns. Food processing industries rely on these kinetic calculations to size industrial conveyor dryers properly. Energy optimization in manufacturing plants depends on predicting exact drying cycle durations. Fifteen minutes is far too short to account for internal diffusion resistance in the falling rate period. Fifty-one minutes underestimates the extended diffusion time required to reach the ten percent moisture level. Ninety-four minutes overestimates the required time based on standard falling rate integration formulas.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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