A slab with a wet weight of 5 kg originally contains 50 percent moisture (wet basis). The slab is 600 by 900 by 75 mm thick. The equilibrium moisture content is 5 percent of the total weight when in contact with air of 20?C and 20 percent humidity. The drying rate is given in Table 24.1 for contact with air of the above quality at a definite velocity. Drying is from one face. How long will it take to dry the slab to 15 percent moisture content (wet basis)?

TABLE 24.1 Wet-slab weight, kg Drying rate, kg/m-h 9.1 4.9 7.2 4.9 5.3 4.4 4.2 3.9 3.3 3.4 2.9 2.0 2.7 1.0