If the filter cake of Example 24.1 is placed on an uninsulated metal pan, conduction through the pan and the wet cake would increase the surface temperature and the drying rate. 

(a) If the change in surface temperature is very small, how much would conduction increase the heat flux to the surface? Assume that k_y = 2k_water.

(b) Estimate the change in surface temperature and the effect on the drying rate.

Example 24.1

A filter cake 24 in. (610 mm) square and 2 in. (51 mm) thick, sup- ported of a screen, is dried from both sides with air at a wet-bulb temperature of 80°F (26.7°C) and a dry-bulb temperature of 160°F (71.1°C). The air flows parallel with the faces of the cake at a velocity of 8 ft/s (2.44 m/s). The dry density of the cake is 120 lb/ft³ (1.922 kg/m³). The equilibrium moisture content is negligible. Under the conditions of drying the critical moisture is 9 percent, dry basis.