Abstract Heat exchangers are fundamental for energy plants and the operation of industrial processes. As a result, active and passive techniques are needed to increase heat transfer and develop efficient and reliable designs. The design of heat exchangers has been based on iterative methods that require experimentation to be validated. These circumstances, added to the development of powerful microprocessors, promote the use of numerical methods to study flow distribution and pressure drop, as well as thermal analyses applying different turbulence models and several coupling speed-pressure schemes. This paper examines flow development through curved and twisted tube heat exchanger by means of a computational fluid dynamics numerical model developed in ANSYS® in order to establish the minimum length required to infer conclusions for the complete exchanger. This work tries to reduce the computational cost while maintaining the balance between desired accuracy and available computational resources. Finally, this study shows that the flow can be considered fully developed after it has traveled 360° inside the helix; after that point, secondary flows and re-circulation regions improve the heat transference in these devices can be verified.