3.6-1. Time for Drying in the Constant-Rate Period. A batch of wet solid was dried on a tray dryer using constant-drying conditions and a thickness of material on the tray of 25.4 mm. Only the top surface was exposed. The drying rate during the constant-rate period was R = 2.05 kg H0/h- m (0.42 lbm H20/h ft). The ratio Lg/A used was 24.4 kg dry solid/m exposed surface (5.0 lbm dry solid/ft). The initial free moisture was X = 0.55 and the critical moisture content Xc = 0.22 kg free moisture/kg dry solid. Calculate the time to dry a batch of this material from X = 0.45 to X = 0.30 using the same drying conditions but a thickness of 50.8 mm, with drying from the top and bottom surfaces. (Hint: First calculate Lg/A for this new case.) Ans. t 1.785 h