Tube-Fin Heat Exchanger

Lytron frequently receives questions through its “Ask an Engineer” website form. A customer recently asked the following question: “While using your heat exchanger selector tool, a warning popped up stating that “Most heat exchangers have a maximum allowable flow rate of 2 GPM.” I was curious as to why 2 GPM is the highest. What are the limiting factors?”

Most standard heat exchangers are designed to operate with a flow rate between 1 gpm and 4 gpm. Increasing the liquid flow rate beyond the optimum range will not necessarily improve the performance of the heat exchanger. What will happen is the heat exchanger will become air-side limited, which means that a much larger fan may be required in order to continue to increase performance. In extreme cases, a commercial off-the-shelf fan will not be adequate to increase the airflow enough to balance the thermal performance. Refer to Lytron’s Integrating a Heat Exchanger into your System: Fan Considerations for more detailed information.

In addition, Lytron’s standard heat exchangers are designed with 3/8″ OD x 0.028″ wall thickness. For many of the smaller heat exchangers, increasing the liquid flow rate much beyond 2 gpm will substantially increase the liquid side pressure drop through the heat exchanger. This means you will need a much larger pump for your cooling system.