Moist extruded catalyst particles are placed as a packed bed (0.5 m thick, 1 m^2) in a through – circulation dryer in which air (density =1.1630 kg/m^3 and viscosity = 18.537 x10^-6 Pa.s) at 300 K and 25 percent relative humidity is passed at a superficial velocity of 0.5 m/s through the particle bed at 1 atm. The equivalent sphere diameter of the particles is 1.30 cm and the bone dry particle density is 1500 kg/ m^3. The particles initially contain 1.8 kg water per kg of dry solid. The equilibrium moisture content is 0.1 kg water / kg wet solid. Upon initial drying of the particles, it was found that constant drying rate persists for 7hrs before it starts to fall. 

Calculate 

(a) the constant drying rate 

(b) the time to dry the particles from 1.8 to 0.6 kg water / kg wet solid 

(c) the drying rate at 0.6 kg water/ kg wet solid