Heat transfer and pressure drop performance of Al2O3/water and TiO2/water nanofluids in tube fitted with simple or modified spiral tape inserts

The present paper deals with the forced convection and pressure drop of Al2O3/water and TiO2/water nanofluids with the presence of inserts in a circular tube. The constant heat flux is maintained around the copper tube with the help of a nichrome wire heater. Two types of inserts are used; simple and modified spiral tape inserts. The modified spiral tape is consisting of zig-zag cuts having notches (or grooves) and projected parts. The Nusselt number, friction factor and thermal performance factor are calculated for different cases: (1) tube with distilled water, (2) tube with distilled water and inserts and (3) tube with nanofluids and inserts. The empirical correlations are developed for all these cases. For Al2O3/water nanofluids, the Nu values decreases with the increase in concentrations, whereas for TiO2/water nanofluids, the Nu values has highest at 0.05% concentration, then there is a decreasing order with the concentrations of 0.075% and 0.1%. it is observed that modified spiral tape inserts with twist ratios of 3.04 and 4.35 effectively enhance the heat transfer without extra penalty of pumping power.