A tunnel dryer is to be designed to dry, by crossflow with air, a wet solid that will be placed in trays measuring 1.5 m long x 1.2 m wide x 25 cm deep. Drying will be from both sides. The initial total moisture content is 116% (dry basis) and the desired final average total moisture content is 10% (dry basis). The air conditions are 90°F and 1 atm with a relative humidity of 15%. The following laboratory data were obtained under the same conditions:

Determine the total drying time to dry the same material from 110% to 10% moisture content if the air conditions are changed to 125°F and 20% relative humidity. Assume that the critical moisture content will not change and that the drying rate is proportional to the difference between the dry-bulb and wet-bulb temperatures of the air. All moisture contents are on the dry basis.

Equilibrium Moisture Content % relative 10 20 30 40 50 60 70 90 humidity Moisture content, 3.0 3.2 4.1 % (dry basis) 4.8 5.4 6.1 7.2 10.7 Drying Test Drying Test Moisture content, Moisture content, % (dry basis) Time, min Time, min % (dry basis) 116 31.4 362 36 28.6 106 415 125 81 465 24.8 194 61.8 506 22.8 211 601 57.4 15.4 242 49.6 635 13.5 277 42.8 785 11.4 313 37.1 822 10.2