Hydrothermal behavior of different hybrid nanofluids in a dimpled tube heat exchanger

The thermal and fluid flow performance of three types of hybrid nanofluid (HNF) inside a dimpled tube was investigated. The water with a dual mixture of Cu particles combined with CuO, TiO2, and Al2O3 nanoparticles (NPs) is used as heat transfer fluid (HTF). The fluid flow and heat transfer were studied numerically using the two-phase mixture and sensitivity analysis was made to reveal the effect of the Reynolds number (Re) and solid volume fraction (& phi;) of HNF on the Nusselt number (Nu), friction factor and overall thermal performance factor. The results demonstrated that under the investigated Re number of 30,000 to 50,000 and & phi; = 0.5% to 1.5%, the highest heat transfer improvement is for Cu-CuO/water HNF and the lowest is for Cu-TiO2/water; also, the improving effect of & phi; increase is more considerable at lower Re numbers. Between different HNFs, the quotient of f/f0 is the highest in the case of Al2O3-Cu/water HNF. The highest value of thermal performance factor is dedicated to HNF of CuO-Cu/water followed by Al2O3--Cu/water and Cu-TiO2/water which average 1.065, 1.055, and 1.039, respectively; also, this factor for Al2O3-Cu/water has the lowest sensitivity to & phi; change and for Cu-TiO2/water has the lowest sensitivity to change of Re number.