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3.7-1. Numerical Integration for Drying in the Falling-Rate Region. A wet solid is to be dried in a tray dryer under steady-state conditions from a free moisture content of X1 = 0.40 kg H2O/kg dry solid to X2 = 0.02 kg H2O/kg dry solid. The dry solid weight is 99.8 kg dry solid and the top surface area for drying is 4.645 m2. The drying-rate curve can be represented by Fig. 33.5-1b. a. Calculate the time for drying using numerical integration in the falling-rate period. b. Repeat, but use a straight line through the origin for the drying rate in the falling-rate period. Ans.(a)t(constant rate) = 2.91 h, t(falling rate) = 6.65 h, t(total) = 9.56 h 2.0 Falling rate Constant rate 1.6 (kg HO) hm? 1.2 0.8 DO Drying rate R 0.4 Xc III 0.1 0.2 0.3 0.4 0.5 0.6 Free moisture X (kg H, 0/kg dry solid) (b) Figure 33.5-1. Typical drying-rate curve for constant-drying conditions: (a) plot of data as free moisture versus time, (b) rate of drying curve as rate versus free moisture content