On the thermal conductivity and viscosity of bionanofluid with neem (Azadirachta indica) assisted zinc oxide nanoparticles

Abstract

Nanofluids which act as coolants in various thermal applications have been promising in accomplishing the primary objective of heat transfer. However, the impact of such fluids on flow lines in the form of enhanced friction factor through unacceptable viscosity rise is an issue to be addressed. On the other hand, these fluids are expected to deteriorate the environment when used or disposed. Hence this research focuses on preparing a bionanofluid and investigating on its primary properties, the thermal conductivity and viscosity. The bionanofluid is prepared by dispersing neem (azadirachta indica) assisted zinc oxide nanoparticles in a binary mixture of ethylene glycol-water (50:50 by volume), at volume concentrations of φ=0.05, 0.2 and 0.5%. To compare the properties of these bionanofluids, additional nanofluids were prepared by dispersing combustion derived pure zinc oxide at same volume concentration. By XRD analysis, the average crystallite size of neem assisted ZnO and pure ZnO was found to be 36 nm and 32 nm. Based on the SEM images, the particles were found to be much closely packed in bioparticles than combustion derived ones. The zeta potential of the nanofluids was found to be 30 mV at pH 6.5, at which the stability is deemed excellent. The thermal conductivity and viscosity of the nanofluids were measured under varying volume concentration and temperature ranging between 20oC and 50oC. Though the thermal conductivity of the conventional ZnO nanofluid is 3.8% higher than the ZnO bionanofluid, the viscosity is 2% lower for the latter than the former, which is highly expected from any nanofluid for an efficient thermal transport.