Experimental study on the convective heat transfer characteristics of MWCNT/Fe3O4 hybrid nanofluid

Abstract

The forced convective heat transfer is the key of heat transfer processes affected by the flow of working fluid. In this study, the convective heat transfer coefficient and friction factor of MWCNT, Fe3O4, and MWCNT/Fe3O4 hybrid nanofluids was investigated experimentally in a heating circular pipe at different Reynolds numbers (1000, 1200, 1400 and 1600). The weight concentrations of 0.025wt%, 0.05wt%, 0.1wt% and 0.2wt% was used in the MWCNT, Fe3O4, and MWCNT/Fe3O4 hybrid nanofluids, and mass mixing ratio of the MWCNT/Fe3O4 hybrid nanofluid was fixed by 1:1 between MWCNT and Fe3O4 nanoparticles. This study is to introduce the basic concept of convective heat transfer, nano-sized nanoparticles, and main problematic prediction of convective heat transfer. First, previous studies reviewed and summarized in the first part. In the second, synthesis method of Fe3O4 nanoparticle, the preparation method of hybrid nanofluid, measurement techniques of thermal conductivities of nanofluids, convective heat transfer experimental setup, and method are presented. In the third, considering all these mentioned elements, enhancement of convective heat transfer coefficient, Nusselt numbers, pressure drop, and friction factors in MWCNT, Fe3O4, and MWCNT/Fe3O4 hybrid nanofluids were comprehensively analyzed. Generally, the convective heat transfer coefficient increases with the Reynolds number and weight concentration of nanofluids, so these phenomenon was verified in this study. The convective heat transfer coefficient of MWCNT/Fe3O4 hybrid nanofluid was ranged from 1914.3 to 1988.4 W/m2K, which was 6%-12.4% higher than that of the base fluid. The maximum improvement in the convective heat transfer coefficient was presented at 0.1wt% MWCNT/Fe3O4 hybrid nanofluid and Reynolds number of 1600, which was 12.4% higher than that of base fluid. The convective heat transfer coefficient of MWCNT/Fe3O4 hybrid nanofluid was 1914.3 W/m2K, 1958.5 W/m2K, and 1988.4 W/m2K, respectively, at weight concentrations of 0.025wt%, 0.05wt%, and 0.2wt%, which were 6%, 8.5%, and 10.1% increased one compared to those of the base fluid. The Fe3O4 nanocomposite synthesized by using the co-precipitation method, which has a magnetic property and has a high potential to improve its thermal properties by adding high thermal conductivity material of MWCNT nanoparticles to Fe3O4 nanofluid. The adding of Fe3O4 nanoparticles into the base fluid can reduce the thermal conductivity of Fe3O4 nanofluid. It may increase the viscosity of the high concentration of nanofluids, which increases the viscous of the layer, therefore the friction factor increases. The MWCNT/Fe3O4 hybrid nanofluid are more effective in the increase the convective heat transfer coefficient compared to single MWCNT and Fe3O4 nanofluids.