Heat transfer and pressure drop studies of TiO2/DI water nanofluids in helically corrugated tubes using spiraled rod inserts

An experimental study on the convective heat transfer and friction factor characteristics of TiO2/DI water nanofluids in uniformly heated plain and helically corrugated tubes (HCT) with and without spiraled rod inserts (SRI) under laminar flow regime is presented in this paper. TiO2 nanoparticles with an average size of 32 nm are dispersed in deionized (DI) water to form stable suspensions containing 0.1, 0.15, 0.2, and 0.25% volume concentrations of nanoparticles. It is found that the inclusion of nanoparticles to DI water ameliorated Nusselt number which increased with nanoparticles concentration upto 0.2%. Two spiraled rod inserts made of copper with different pitches (pi = 50 mm and 30 mm) are inserted in both plain and corrugated tubes and it is found that the addition of these inserts increased the Nusselt number substantially. For Helically corrugated tube with lower pitch and maximum height of corrugation (pc = 8 mm, hc = 1 mm) with 0.2% volume concentration of nanoparticles, a maximum enhancement of 15% in Nusselt number is found without insert and with insert having lower pitch (pi = 30 mm) the enhancement is 34% when compared to DI water in plain tube. The results on friction factor show a maximum penalty of about 53.56% for the above HCT.