This research presents numerical investigation of pipe heat exchanger with twisted tape inserted inside and helical fins on outside pipe surface. Various configurations were modelled based on the twist pitch (p) inside the pipe and fin twist pitch (P) over outside of the pipe. The fin twist pitch P (P = P, 2P/3, P/2) on the pipe outside and the inserted tape twist pitch p (p = p, 3p/2, p/2) inside the pipe was varied in the investigation. The hot fluid (water) passes inside the pipe, while the cold fluid (water) passes on the outside of pipe in counter flow direction. The Dittus-Boelter correlation was used for validation. For smooth pipes and the proposed heat exchanger with twisted tapes and helical fins, numerical results were compared. It was found that in inside and outside flows, twisted tape formed longitudinal vortex that helped to increase fluid mixing, thus being higher than that of smooth tube heat transfer rate. © 2021 Elsevier Ltd. All rights reserved.