Pressure drop and thermal transfer performances in exchangers, why do they increase together?

There is a little trick that I’m explaining here related to the functioning and thermal transfer efficiency of heat exchangers: why the performances increase while the pressure drop increases?

The thing is simple: when we allow increased pressure drops on the fluid’s flow rate within an exchanger, and thus pressure drop of water circulating within the shell or the tubes, or on the two sides of a plate heat exchanger, we obtain a boost in performances. That’s because, being equal the section of the exchanger, increasing the pressure drop means that we are increasing the flow rate. Even better said, when we are accepting higher pressure drops, that means that we can reduce the passage section of the fluids and thus increase their flowing speed.

That leads to a more turbulent flow of fluids, which in the exchanger involves a higher number of collisions among the particles of the fluid and thus a higher thermal transfer rate. That’s why the thermal transfer efficiency increases too.

The same thing can be done for a pre-existing exchanger, where in order to boost the thermal transfer performances we can simply increase the flow rate, which correspond in quite a linear ratio to an increase of pressure drop and therefore of the performance of the heat exchanger.

This is a tiny good trick that is valid in the design of heat exchangers, both for plate heat exchangers or shell and tube exchangers, and for any kind of heat exchanger.