Numerical investigation of heat transfer enhancement inside heat exchanger tubes fitted with perforated hollow cylinders

This paper investigates the flow structure and thermal performance characteristics of the fluid flow through a heat exchanger tube fitted with perforated hollow cylinders (PHCs) under turbulent flow regime. The effects of the perforated index (0.08 < PI < 0.24), diameter ratio of the hollow cylinder (0.5 < d/D < 0.9) and Reynolds number (6000<Re<16000) on the thermal performance and heat transfer enhancement are investigated. The vortex flow generated near the holes leads to better fluid mixing between the tube wall and the core regions and this recirculating flow enhances the heat transfer rate in comparison with a plain tube. The numerical results indicate that the flow resistance can be reduced up to 86.2% with increasing the perforated index from 0.08 to 0.24. The maximum thermal performance value of 1.456 could be achieved for the case of d/D = 0.74 and PI = 24% at Re = 6000. The results show that the fluid mixing between the core region and the tube walls for the case of 0.7 is higher than the other cases. Therefore, the heat transfer rate is expected to be better for the case of PI = 0.08 and d/D = 0.7 due to the thermal boundary layer destruction caused by the PHCs.