<b>Experimental Study on the Effect of CuO DI Water Nanofluids on Heat Transfer and Pressure Drop in a Circular Tube with Inserts</b> In this experimental study, convective heat transfer and friction factor characteristics of CuO DI water nanofluids flowing through a plain tube with spiraled rod inserts SRI is studied. The experiment is conducted under laminar flow and constant heat flux conditions. CuO nanoparticles are dispersed in Deionized DI water to prepare CuO DI water nanofluids with 0.1 volume concentration of nanoparticles. From the experimental results, it is found that the inclusion of nanoparticles in DI water enriches the Nusselt number. The enhancement in Nusselt number is 19 at Re 2240 for a plain tube with nanofluids of 0.1 volume concentration compared to DI water. Two copper SRIs with pitches 50 mm and 30 mm are used which increased the Nusselt number by 35.9 and 37.2 respectively with nanofluids of 0.1 volume concentration compared to DI water. The estimated friction factor with the use of nanofluids is 4.2 more than the DI water, which is an insignificant one, so there is no penalty in pumping power. CuO DI Waternanofluids, Laminarflow, Heat transfer enhancement, frictionfactor 222-226 Issue-3 Volume-5 P. Arunkumar | S. Anbu | K. Velmurugan | K. Gurunath