Example 9.1: (HW7/Q3) A waste heat recovery heat exchanger consists of a long tube carrying water in a large chimney in cross-flow configuration (Figure 3). The exhaust gas temperature coming through the chimney is 250C. The velocity of the exhaust gas 8 m/s. The water tube has an outer diameter of 25 cm and inner diameter of 20 cm and the tube material (an alloy of tin) has a conductivity of 60 W/mK. Water at a flow rate of 0.15 kg/s enters the tube at 15C and exits at 70C. Assume the internal water flow is both thermally and hydrodynamically fully developed, and the outer and inner surface temperatures of the tube is uniform. Assume the chimney to be large enough so that the gas flow around the tube is not affected by chimney walls. Treating the system as a heat exchanger, what would be the overall heat transfer coefficient? Exhaust Water) Figure 3: Waste heat re- covery system Average properties of the exhaust gas: pe = 0.78 kg/m, Me = 25.110-7 N-s/m, ke = 0.038 W/mK, Pre = 0.701 Average properties of water: v= 1.00910- m/kg, w = 631x10-6 N-s/m, k = 0.634 W/mK, Prw = 4.16