(Solution) - A 5 m long twin tube counter flow heat exchanger -(2025 Original AI-Free Solution)

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A 5-m-long, twin-tube, counter flow heat exchanger, such as that illustrated in Problem 11 .29, is used to heat air for a drying operation. Each tube is made from plain carbon steel (k = 60 W/m ? K) and has an inner diameter and wall thickness of 50 mm and 4 mm, respectively. The thermal resistance per unit length of the brazed joint connecting the tubes is R't = 0.01 m ? K/W. Consider conditions for which air enters one tube at a pressure of 5 atm, a temperature of 17°C, and flow rate of 0.030 kg/s, while saturated steam at 2.455 bar condenses in the other tube. The convection coefficient for condensation may be approximated as 5000 W/m2 ? K. What is the air outlet temperature? What is the mass rate at which condensate leaves the system?