The maximum transferred heat energy of a heat exchanger is not only dependent on the size of the exchange surface area and the heat transfer coefficient (k), important is also the flow directions of the media. If both media flow in the same direction it is called direct current principle when opposed by counter-current flow. The flow direction, is crucial for the mean temperature difference between the two media.
 

         

 

Theoretical analysis of the two connection options:

For the analysis, we assume that there are two media with the same heat capacity and the same mass flow.

Fluid 1: 80°C
Fluid 2: 20°C

The maximum achievable temperature for the direct current principle for both media will be 50 ° C, this would correspond to the mixing temperature.
For counter-flow principle, the maximum achievable temperature for medium 2 will be 80 ° C
and for media 1: 20 ° C.

Consequently, will be by using the counter-flow principle, the temperature difference larger and more thermal energy will be transmit.

Formula for calculation: