A comprehensive review of preparation, characterization, properties and stability of hybrid nanofluids

Nanofluids are emerging as promising thermo fluids for heat transfer application. Nano fluids are two phase fluids of solid liquid mixture. The presence of solid nanoparticles in the base fluid increases significantly the effective thermal conductivity of the fluid and consequently enhances the heat transfer characteristics. Addition of single nanoparticle in base fluid, to improve the flow and heat transfer characteristics of the base fluid is a proven technology. In recent years, attention is focused on research studies involving impregnation of two or more nanoparticles in base fluids, called hybrid or composite nanofluids. Research studies on nanofluid containing composite nanoparticle showed better enhancement in thermal and rheological characteristics of base heat transfer fluid compared to mono nanoparticle based nanofluids. The research studies carried out on preparation, characterization, properties and stability of hybrid nanofluids are comprehensively reviewed in this paper. The models for properties such as thermal conductivity, viscosity, density, specific heat, friction factor and heat transfer coefficient of hybrid nanofluids are presented. The potential application and the challenges including stability methods and measures for hybrid nanofluids are discussed.