Entropy generation analysis of turbulent convection in a heat exchanger with self-rotating turbulator inserts

Turbulator inserts are commonly applied to enhance the thermal performance of heat exchangers with an accompanying rise in pressure drop due to the generation of the secondary swirl flow. We study the effect of inter-turbulator distance of rotating turbulator inserts on the heat transfer enhancement and entropy generation of forced convection in the turbulent flow region of a heat exchanger. Attributed to the turbulator inserts, the maximum rise of Nusselt number is 360% and 240%, for non-rotating and rotating cases, respectively, while the friction factor is increased significantly in the flow disturbed by the turbulator inserts. The Nusselt number and friction factor are augmented as the inter-turbulator distance is reduced. The partitioning of tube by the turbulator insert induces the swirl flow that leads to the enhancement of forced convection. From the second-law analysis, the entropy generation rate of the non-rotating case increases up to 202% comparing to that of the rotating case. This shows that the rotating turbulator insert is a more thermodynamically advantageous configuration, as it enhances the thermal performance appreciably while reducing the entropy generation significantly.