Answer:
The diagram presented is useful to understand the difference between these two types of exchange, which represents two fluid streams that travel parallel separated by a semipermeable or thermo-conductive membrane. The blue color represents the lowest value of the characteristic to be exchanged, while the red color indicates the highest value, so that the direction of the transfer will be of the fluid with the highest value to the lowest value. In the specific case of heat, the movement follows the second law of thermodynamics and in the case of solids as solutes the phenomenon of osmosis is followed. Exchange in equicorrent and countercurrent.
Direct flow
In this system the two fluids go in the same direction and their gradient varies along the flow path. Taking into account that the fluid present in the two tubes is the same, this method of exchange is only capable of exchanging half of the property (heat, matter, concentration, etc.) between fluids, no matter how long the flow path If either of the two currents changes their property by 50% or more, the exchange will be interrupted since the gradient is reduced to zero, indicating that the equilibrium point has been reached. In case of having unequal flows, the equilibrium conditions will be a little closer to the conditions of the current that has the greatest flow.
