The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U_{0} = 400 W/m^{2}.K. The fouling factor after one year of operation is found to be h_{d0} = 2000 W/m^{2}.K. The overall heat transfer co-efficient at this time is

In a laboratory test run, the rate of drying was found to be 0.5 x 10^{-3} kg/m^{2}.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m^{2}/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is