A hot stream provides 2 kg/s at 200 C, with specific heat 3 kcal/kg C. A cold stream is available at 30 ^οC and with specific heat of 2 kcal/kg ^οC. 

1. Determine the flowrate of the cold stream required to cool the hot stream to 100 ^οC. Determine the exergy efficiency of this heat exchange system. 

2. Repeat step 1 for a cold stream final temperature of 50 ^οC. 3. Explain the difference in the two exergy efficiencies.