Solutions to selected self-study problems

Q09. An insoluble granular material wet with water is being dried in a pan 0.457 × 0.457 m and 25.4 mmdeep. The material is 25.4 mm deep in the metal pan, which has a metal bottom of thickness z M = 0.610mm having a thermal conductivity k M = 43.3 W/m.K. The thermal conductivity of the solid can be assumedas k S=0.865 W/m.K. Heat transfer is by convection from an air stream following parallel to the top dryingsurface and the bottom metal surface at a velocity of 6.1 m/s and having a temperature of 65.6 °C andhumidity H = 0.01 kg H 2O / kg dry air. The top surface also receives direct radiation from steam heatedpipes whose surface temperature T R = 93.3 °C. The emissivity of the solid is ε = 0.92. Estimate the rate ofdrying for the constant-rate period.State all assumptions you make.Examine the following1. Effect of changing air velocity to 8 m/s , other parameters being held constant2. Effect of reducing humidity to 0.005 kg/kg, other parameters held constant3. Thickness of the bed reduced to 15 mm, other parameters held constant4. If instead of drying air flowing parallel to the drying surface, what if we use an array of impinging jets?Comment on this design suggestion.