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In this article, a 3D numerical simulation for investigating friction factor and heat transfer enhancements in case of inserting normal or perforated dual twisted tapes (TTs) in converging‐diverging tubes (CDTs) is presented. The effects of Reynolds number changing from 10,000 to 20,000 and a various number of holes (N = 0, 1, 2, and 3) in TTs, under constant uniform heat flux on tube outer wall and using water as working fluid circumstances, were examined. It was found that generally using dual TTs in CDTs improves the Nusselt number up to 9% compared to bare CDTs. Perforating TTs do not have a noticeable effect on heat transfer, but decrease the friction factor significantly, up to 396% compared to normal dual TT implantation, in higher Reynolds numbers. Following that, thermal performance factor considerably increases up to 57%, compared to CDTs with normal dual TTs. To show the mechanism of these effects, velocity streamlines are presented and will be discussed in this paper.