Spray drying is a process in which a liquid containing dissolved or suspended solids is injected into a chamber through a spray nozzle or centrifugal disk atomizer. The resulting mist is contacted with hot air, which evaporates most or all of the liquid, leaving the dried solids to fall to a conveyor belt at the bottom of the chamber.

Powdered milk is produced in a spray dryer 6 m in diameter by 6 m high. Air enters at 167?C and ?40 cm H₂O. The milk fed to the atomizer contains 70% water by mass, all of which evaporates. The outlet gas contains 12mole% water and leaves the chamber at 83?C and 1 atm (absolute) at a rate of 311 m³/min

(a) Calculate the production rate of dried milk and the volumetric flow rate of the inlet air. Estimate the upward velocity of air (m/s) at the bottom of the dryer.

(b) What problem would you guess would occur if the velocity is too high?

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Milk (70% H₂O) Inlet air 167°C, -40 cm H₂O Dried milk Wet air 311 m³/min 83°C. 1 atm