In accordance with the concept of the flow arrangement, there are two main classifications
of the heat exchangers. The first kind is known as the parallel flow heat exchangers. In these cases, the entrance of the fluids within the exchangers occurs at the same time. The second important kind of heat exchanger is known as the counter exchangers. The entrance of the fluids in the exchangers is in the opposite direction. This is an important example of one of the most efficient heat exchangers. One of the main facts based on which this kind of heat exchanger is most efficient is that the transfer of heat from the medium to the space is efficient. In this case, the difference of an average temperature between the environment and the medium is lesser. The third kind is known as the cross flow heat exchanger. The fluids in the case of this heat exchanger travel in an opposite direction to each other.
For increased efficiency, it is important that the surface area of wall between the two fluids
is increased for maximum heat exchange. With the help of the material chosen for the heat exchanger, the resistance of flow can be reduced. The heat exchangers can be used for many purposes and these include residential as well as industrial purposes. It has been seen that in the presence of fins or any kind of corrugations can reduce the efficiency of the heat exchangers. These are the fins or corrugations that increase turbulence by often increasing the surface area.