Thermal performance evaluation for alumina coated MWCNTs composite nanofluid in annular passage of various eccentricities

Abstract

In this paper, numerical and experimental work was conducted to evaluate Al2O3-MWCNTs/DW hybrid nanofluids thermal performance in an annular passage of various eccentricities under fully developed turbulent flow conditions. A composite nanoparticle of 60 wt% Al2O3 and 40 wt% f-MWCNT was used to prepare 0.1 wt%, 0.075 wt%, and 0.05 wt% hybrid nanofluid. The numerical work was performed by building a 3-D domain for annular passage of 1 m length and diameter ratio of 2 with a heated inner pipe and an insulated outer pipe using ANSYS-Fluent package. The effects of the Reynolds number (6000–11,000), the nanoparticles weight concentration and the eccentricity on the average Nusselt number and pressure drop were investigated. The nanofluids thermal conductivity showed an average enhancement of 3.102%, 1.829%, and 1.158 for the concentrations 0.1 wt%, 0.075 wt%, and 0.05 wt%, respectively. The maximum enhancement of the convection heat transfer coefficient for the concentric case was 6.49%, 4.86% and 2.98% for the concentrations 0.1 wt%, 0.075 wt% and 0.05 wt%, respectively. By evaluating the performance index, the nanofluids are good alternative whenever the enhancement in heat transfer is only considered, regardless of its passive effects on pressure drop and pumping power.