P1 Exhaust gases from a power plant are used to preheat air

P-1) 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 oC and leave at 200oC. The air enters the heat exchanger at 70oC, leaves at 250 C, and has a mass flow rate of 10 kg/s. sume 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 un

Solution

For the above given data for heat exchanger

For first case

Surface area= 65m2

For second case

Surface area= 45m2