Convective heat transfer studies in a circular tube with swirl promoters using neem assisted zno nanofluids

Abstract

Nanofluids are used as coolants in many thermal applications and they have been a promising technology in achieving the primary objective in heat transfer. However, the impact of such fluids on flow lines has an improvement in the friction factor by raising the viscosity to an acceptable limit and this issue is to be foccused. Moreover, these fluids deteriorate the environment while using or when disposed of. Therefore, this research work focuses on the preparation of a bionanofluid, investigation of its properties and hence evaluating the convective performance through flow experiments. The bionanofluid was prepared by combining neem (Azadirachta Indica) assisted zinc oxide nanoparticles with a binary mixture of ethylene glycol-water in the ratio of 1:1 by volume, at different volume concentrations (and#61542;) such as 0.05%, 0.2%, and 0.6%. Further, to compare the properties of these bionanofluids, additional nanofluids were prepared by dispersing combustion-derived pure zinc oxide at the same volume concentration. By using the X-Ray Diffraction (XRD) analysis, the average crystallite size of the neem assisted ZnO and pure ZnO was found to be 36 nm and 32 nm respectively. Furthermore, based on the Scanning Electron Microscopy (SEM) images, the nanoparticles were found to be closely packed in bioparticles than the combustion derived ones. The zeta potential of the nanofluids was found to be 30 mV at pH 6.5, at which the stability was found to be very high. Moreover, the thermal conductivity and the viscosity of the nanofluids were measured under different volume concentrations and temperatures in the range from 20oC to 50oC. The average enhancement in the density, viscosity, specific heat and thermal conductivity of pure ZnO based nanofluids are 4.7%, 7%, 1.1% and 4.3%, whereas for neem assisted ZnO the values are 5.2%, 4.1%, 1.4% and 3.2%. Though the thermal conductivity of nanofluids with neem assisted ZnO is marginally lower than that of pure ZnO, the density, specific heat and viscosity values are in such a way tha