You were recently hired as a process engineer by a pulp and paper manufacturing firm. Your new boss calls you in and tells you about a pulp dryer designed to reduce the moisture content of 1500 kg/min of wet pulp from 0.9 kg H₂O/kg dry pulp to 0.15 wt% H₂O. The design called for drawing atmospheric air at 90% relative humidity, 25°C, 760 mm Hg into a blower that forces the air through a heater and into the dryer. When the operation was put into service, weather conditions were exactly as assumed in the design, and measurements showed that the air leaving the dryer was at 80°C and a gauge pressure of 10 mm Hg. However, there was no way to check the operation of the blower to see if it was delivering the specified volumetric flow rate of air. Your boss wants to check that value and asks you to devise a method for doing so. You go back to your office, sketch the process, and determine that you can estimate the air flow rate from the given information if you also know the moisture content of the air leaving the dryer. 

(a) Propose a method to estimate the moisture content of the exit air. 

(b) Suppose your measurement is carried out and you learn that the exit air at 10 mm Hg gauge has a dew point of 40°C. Use that information and the mass of water removed from the wet pulp to determine the volumetric flow rate (m³/min) of air entering the system.