Active and passive methods can be used to enhance heat transfer accounting for increase in overall performance of double pipe heat exchanger. In our present study, efforts have been carried out to enhance the heat transfer in a square heat exchanger by adding geometrical modifications to the flow channel by incorporating inserts, i.e., a twisted tape. Tapes with constant cross section and varying twist ratios were placed in the centre of a square heat exchanger subjected to varying turbulent flow rates of Re 2500 to 10000 of water at 298K. The external wall of the heat exchanger was maintained at a constant temperature of 333K. Numerical simulation was carried out using ANSYS-15. Numerical results led to a conclusion that heat transfer rate was enhanced by decreasing the twist ratio of the tape and by increasing the Reynolds number of water flow. Results indicated an increase in Nusselt number and heat transfer for twisted tape compared to the bare tube for all mass flow rates.