If a closed feedwater heater is functioning properly, what should be the temperature of the feedwater as it exits the heater?

When a closed feedwater heater is operating correctly, the feedwater temperature as it exits the heater should be only slightly below the temperature of the steam that is being used to heat it. This is typically in the range of 2 to 5 degrees below the steam temperature.

This slight differential is due to the principle of thermodynamic efficiency and heat exchange. The steam transfers its heat to the feedwater without direct contact, and maintaining a small temperature drop maximizes the efficiency of heat transfer while minimizing heat loss. A feedwater temperature too far below the steam temperature could indicate issues with heat transfer efficiency, while a temperature above the steam temperature would not be achievable in a closed system, where the purpose is to heat the water close to the steam's temperature without exceeding it.

This understanding of the optimal operational range is crucial for maintaining the efficiency and effectiveness of the closed feedwater heating system.