In evaporator design, the approach temperature is defined as the difference between the refrigerant boiling temperature and which water temperature?

• A. Suction-water temperature
• B. Leaving-water temperature
• C. Inlet-water temperature
• D. Head pressure

Answer: (B)

Approach temperature in evaporator design is the difference between the refrigerant’s saturated boiling temperature and the leaving-water temperature. This difference shows how close the water exiting the evaporator gets to the refrigerant’s boiling temperature, which indicates how effectively heat is being transferred. A smaller approach temperature means the water leaves nearer to the refrigerant temperature, signaling better heat transfer and more efficient use of the evaporator surface. The relevant pair is the refrigerant’s boiling (saturation) temperature and the water’s leaving temperature because they are the two streams exchanging heat. The suction-water temperature, the inlet-water temperature, and head pressure do not define this approach.