An evaporative cooler for an automobile consists of an 18-in-long by 8-indiameter cylinder that hangs on the outside of the car. At 55 mph the cooler processes 4500 lb_m of dry air per hour. During desert driving, the air is at 100 F with 10% relative humidity. Inside the cooler, the air passes through a moistened burlap cloth and leaves the cooler at 80 F. This cooled air flows through a duct to the passenger compartment. The cooler can be considered adiabatic, and all processes occur at 14.7 psia. The burlap moisture is supplied from a 5-gal container outside the car at 100 F. Kinetic energy changes are negligible.

A. Determine the humidity ratio and the dew point (F) of the desert air.

B. Determine the relative humidity of the processed air entering the car.

C. If the container is full at the start, determine the time (hr) for which the car can be driven at these conditions before the 5-gal container runs dry.