Investigating the effect of together usage of circular depressions and different Nano-particles for thermal performance improvement of coiled tube

Present paper is a numerical simulation which probes the effect of Nano-particles and circular depressions on performance of helical tube. The pitch of depressions and the type and the volume fraction of Nano-particles were considered as variants of the present investigation. Nano particles included, Cu and Al2O3 particles with volume fraction of 2,3 and 4 percent. Flow was considered to be in turbulent regime and the Dean number was within the range of 2600-7000. Tube was put under constant heat flux of 2500 W/m2. Thermal and frictional behavior of helical tube together with performance index of helical tube in case of having circular corrugation and Nano-particles were evaluated. It was found that the application of corrugations changes flow structure and leads in heat transfer augmentation. Furthermore, it was revealed that circular corrugations increase the heat transfer rate by up to 98%. Besides, application of Al2O3 and Cu Nano particles together with corrugations increases heat transfer rate up to 104% and 108%, respectively. It was found that maximum performance index was about 1.17 which was observed for the tube with pure water and circular corrugations. Also, it was found that application of circular corrugation is more beneficial within Dean number of 2600 and 5800.