A dry solid mass of 200 kg undergoes drying for 5000 seconds during the constant-rate period at Nc = 0.5 × 10-3 kg/m2.s. Initial moisture is 0.2 kg/kg dry solid with an interfacial area of 4 m2 per 1000 kg dry solid. The final moisture content (in kg moisture/kg dry solid) is?
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Answer: C. 0.1
Explanation
Constant-rate drying equations relate moisture evaporated over time to drying rate and area. Multiplying drying rate by interfacial area and time yields total moisture mass evaporated. Subtracting evaporated moisture from initial solid moisture results in a final moisture content of zero point one. Constant-rate drying period occurs when liquid evaporates freely from a saturated solid surface. Moisture content in drying calculations is expressed as mass of moisture per unit dry solid mass. Interfacial area determines the effective surface available for mass transfer during drying.
Agricultural product drying operations use constant-rate drying models to estimate processing times. Pharmaceutical powder manufacturing relies on accurate drying kinetic calculations to control moisture. Chemical engineering design of industrial dryers requires precise initial and final moisture balances. A final moisture content of zero point five overestimates moisture retention during drying operations. Zero point zero five results from arithmetic errors in mass balance moisture calculations. Zero point fifteen fails to match the correct integration of constant-rate drying equations.
- Subject
- Engineering
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- Chemical Engineering
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- Difficulty
- medium
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