An air preheater for a power plant consists of a cross-flow heat exchanger with hot exhaust gases used to heat incoming air a 1 atm and 300 K. The gases enter at 375°C with a flow rate of 5 kg/s. The air flow rate is 5.0 kg/s, and the heat exchanger has A = 110 m2 and U = 50 W/m2 ? °C. Calculate the heat-transfer rate and exit temperatures for two cases, both fluids unmixed and one fluid mixed. Assume the hot gases have the properties of air.