Project ForgeMass Transfer
Mass Transfer Operations
GATE 2018
Hard
A fiberboard sheet (1.5m×2.0m×15mm, drying from top and bottom only) weighs 16kg wet at 60% moisture (dry basis), drying at a constant rate of 1.25×10⁻⁵ kg/m²·s until moisture falls to 30%. The time (hours) for the constant-rate period is (rounded off to third decimal place)
11.11 hours(± 0.2 accepted)
Explanation
Dry solid mass=16/1.6=10kg. Moisture removed=10×(0.6−0.3)=3kg. Drying area=2×(1.5×2.0)=6m². Rate=1.25×10⁻⁵×6=7.5×10⁻⁵ kg/s. Time=3/7.5×10⁻⁵=40,000s=11.11h.
Source: GATE CH 2018 (2018)
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