Project ForgeConsider a drying operation for a solid loading (dry basis) of 50 kg/m² with a constant drying rate of 5 kg/m².h. The falling rate of drying is linear with moisture content, with critical moisture content Xc=0.1 and equilibrium moisture content Xe=0.005 (both kg H2O/kg dry solid). The drying time (in hrs) required to reduce an initial moisture content of 25% to a final moisture content of 2% is
- A1.55
- B1.75
- 3.25
- D4.55
Explanation
Constant rate period (X0=0.25 to Xc=0.1): t=Ls(X0−Xc)/(A·Rc)=50×0.15/5=1.5 h. Falling rate period (Xc=0.1 to Xf=0.02, linear rate through Xe=0.005): t=[Ls(Xc−Xe)/(A·Rc)]·ln[(Xc−Xe)/(Xf−Xe)]=(50×0.095/5)·ln(0.095/0.015)=0.95×1.846=1.75h. Total=1.5+1.75=3.25 h.
Source: GATE CH 2012 (2012)
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