Numerical investigation of different geometrical parameters of perforated conical rings on flow structure and heat transfer in heat exchangers

A numerical study has been performed to investigate the flow and heat transfer characteristics of fluid flow through heat exchanger tubes fitted with perforated conical rings. The holes are circular, and the number of holes N is ranged from 0 to 10. The influences of perforated conical ring diameter ratios D₂/D₁=0.4,0.5and0.6 and the hole diameter ratios d/D=0.06,0.1and0.14 on average Nusselt number, friction factor and thermal performance factor are reported. This analysis is performed in the turbulent flow regime 4000⩽Re⩽14,000 and the governing equations are solved by using (RNG) k-∊ model. Due to strong turbulent intensity, perforated conical rings lead to more flow perturbation and fluid mixing between walls and the core region, which has a significant effect on heat transfer enhancement. The recirculating flow through the holes can also improve the heat transfer and reduce the pressure drop through the heat exchanger tube. The results show that the Nusselt number is reduced up to 35.48% by increasing the number of holes from 4 to 10. The maximum thermal performance factor of 1.241 is obtained for the case of N=10, d/D=0.1 and D₂/D₁=0.6 at Reynolds number of 4000.