An air cooler uses steel pipes within a shell to cool 200 kg/hr of air from 85°C to 30°C. The air flows through tubes while cooling water flows through the shell of a 1-shell, 2-tube pass heat exchanger. Given heat transfer coefficients and costs, the optimum exit temperature of the cooling water and optimum length of tubes need to be calculated to most efficiently cool the air.

1. Aguila, Amanda Blaza, Christine Cotiangson, Manuel Palicpic, Lizette

5. An air cooler consisting of a bundle of 1” Sch 40 steel pipes enclosed in a well baffled shell is being built to cool 200 kg/hr of air from 85 o C to 30 o C. The air flows under pressure through the tubes of a 1-shell 2-tube pass heat exchanger. Cooling water at 20 o C is under sufficient pressure to force it through at any desired rate, flows through the shell. The heat transfer coefficient based on the inside fluid is 48 W/m 2 K and for the outside fluid, 2000 W/m 2 K. Cooling water costs PhP 0.57/m 3 and the annual fixed charges is 20% with cooler cost at PhP 24,000/m 2 . Calculate the Optimum exit temperature of cooling water and optimum length of tubes.