4.12 WP As shown in Fig. P4.12, air with a volumetric flow rate of 15,000 ft/min enters an air-handling unit at 35F, 1 atm. The air-handling unit delivers air at 80F, 1 atm to a duct system with three branches consisting of two 26-in.-diameter ducts and one 50-in. duct. The ve locity in each 26-in. duct is 10 ft/s. Assuming ideal gas behavior for the air, determine at steady state a. the mass flow rate of air entering the air-handling unit, in lb/s. b. the volumetric flow rate in each 26-in. duct, in ft/min. c. the velocity in the 50-in. duct, in ft/s. ans: 20 lb/s, 2210 ft^3/min, 14.6 ft/s