In heat exchangers, degree of approach is defined as the difference between temperatures of

Degree of approach in a heat exchanger is a measure of how close the outlet temperatures of the two fluids get to each other.

Specifically, it is defined as the temperature difference between the hot fluid outlet and the cold fluid outlet.

Option A: Cold water inlet and outlet → This represents the temperature rise of the cold water, not the degree of approach.

Option B: Hot medium inlet and outlet → This represents the temperature drop of the hot medium, not the degree of approach.

Option C: Hot medium outlet and cold water inlet → This does not directly indicate how close the fluids are to thermal equilibrium at the outlet.

Option D: Hot medium outlet and cold water outlet → This is correct. It shows how efficiently the heat exchanger transfers heat. A smaller degree of approach means the fluids are approaching the same temperature at the exit, indicating better heat transfer performance.