Water enters a heat exchanger at 85°C with a flow rate of 2.5 kg/s. Dry atmospheric air enters the heat exchanger at 20°C at a flow rate of 12 kg/s. It is desired to select a cross flow heat exchanger for this task such that the air leaves the heat exchanger at a temperature near, but not less than, 60°C. The design engineer is considering three possible cross flow heat exchangers that have been identified as viable solutions to accomplish this task;

a. Calculate the outlet temperature of the air for the three heat exchangers. Is the minimum outlet temperature of 60°C satisfied?

b. Calculate the effectiveness of each of the heat exchangers. Is there an advantage to one configuration over the others?

c. Which heat exchanger would you recommend, and why?

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HXI: both fluids unmixed (UA = 23.5 kW/K) HXII: Cmin mixed with max unmixed (UA = 32.0 kW/K) HXIII: Cmax mixed with min unmixed (UA1 = 32.8 kW/K)