Abstract
In the present experimental work, the convective heat transfer coefficient and friction factor for fully developed turbulent flow of MWCNT-Fe3O4/water hybrid nanofluids flowing through a uniformly-heated-at-constant-heat-flux circular tube are estimated. The MWCNT-Fe3O4 nanocomposite was prepared by in-situ method, which includes the dispersion of carboxylated carbon nanotubes in distilled water and mixing of ferrous chloride and ferric chloride. Sodium hydroxide was used as reducing agent to form MWCNT-Fe3O4 hybrid nanocomposite. The detailed surface and magnetic properties were performed by X-ray diffraction and scanning electron microscopy, and using a vibrating sample magnetometer. The stable hybrid nanofluids were prepared by dispersing nanocomposite in distilled water, and the heat transfer and friction factor experiments were conducted for particle loadings of 0.1% and 0.3%. The results indicate a maximum of 31.10% enhancement in Nusselt number with a penalty of 1.18-times increase of pumping power for the particle loading of 0.3% at a Reynolds number of 22,000 as compared to base fluid data. The empirical correlations were proposed for the estimation of Nusselt number and friction factor to match well with the experimental data. (C) 2014 Elsevier Ltd. All rights reserved.