A 25 wt% solution of coffee in water at 70°F is spray dried to a final moisture content of 5% (dry basis) with air that enters at 450°F and 1 atm with a humidity of 0.01 lb/lb (dry basis) and exits at 200°F. Assuming a reasonable value for the specific heat of coffee, calculate:
(a) The air rate in lb dry air/lb coffee solution.
(b) The temperature of evaporation.
(c) The heat-transfer rate in Btu/lb coffee solution.