Chapter 11, Problem 11.67P

Exhaust gas from a furnace is used to preheat the combustion air supplied to the furnace burners. The gas,which has a flow rate of 15 kg/s and an inlet temperatureof 1100 K, passes through a bundle of tubes, while theair, which has a how rate of 10 kg/s and an inlet temperature of 300 K, is in cross flow over the tubes. Thetubes are unfinned, and the overall heat transfer coefficient is ${\text{100 W/m}}^2\cdot \text{K}$ . Determine the total tube surfacearea required to achieve an air outlet temperature of850 K. The exhaust gas and the air may each beassumed to have a specific heat of $\text{1075 J/kg}\cdot \text{K}$ .