Exhaust gases from a power plant are used to preheat air in a cross-flow heat exchanger. The exhaust gases enter the heat exchanger at 450?C and leave at 200?C. The air enters the heat exchanger at 70?C, leaves at 250?C, and has a mass flow rate of 10 kg/s. Assume the properties of the exhaust gases can be approximated by those of air. The overall heat transfer coefficient of the heat exchanger is 154 W/(m2 K). Calculate the heat exchanger surface area required if(a) The air is unmixed and the exhaust gases are mixed and(b) Both fluids are unmixed.GIVENCross-flow heat exchanger ?? exhaust gas to airExhaust temperaturesTe,in = 450?CTe,out = 200?CAir temperaturesTa,in = 70?CTa,out = 250?CAir flow rate (ma) = 10 kg/sOverall heat transfer coefficient (U) = 154 W/(m2 K)ASSUMPTIONSThe properties of the exhaust gases can be approximated by those of airThe air is in thetube

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Alr Tah=70°C Exhaust Tan=450°C Ta out = 200°C Te out- 250°C