A granular polymeric material is to be dried by blowing air through the material in a fixed bed. The thickness of the bed is 7 cm. the bed porosity is 0.60, and the specific area of the solid particles in the bed is 185 m2/m3. The particle average diameter is 0.013m and the dry solid bulk density is 640 kg/m3. The dry solid density is 1600 kg/m3. Air at 55oC and a wet bulb temperature of 25oC is used to dry the wet material. Air mass flux is 2592 kg/m2.h. Average air viscosity is 2.15x10-5Pa.s. The latent heat of evaporation of water at the wet bulb temperature is 2442 KJ/kg.
a) Estimate the required drying time to reduce the total moisture content of the material from 0.70 kg water/kg of dry solid to 0.10 kg water/kg of dry solid. The equilibrium moisture content of the material under the given conditions is 0.010 kg water/kg of dry solid. The critical free moisture content is 0.080 kg water/kg of dry solid (30 marks)?
b) If humidity of the inlet air is increased to 0.0127 kg water vapour/kg dry air (same other conditions), would the drying time increase or decrease and by how much (10 marks)?
c) If the gas mass flow rate is reuced to 50% of the original flow rate, what would the requir3ed drying time be? (10 marks)
CHE 318 Separation Processes midterm test 2013
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