Challenges in hybrid nanofluids behavior in turbulent flow: Recent research and numerical comparison

Numerical and experimental researches on nanofluids have increased rapidly over the last few years. In spite of some inconsistent reports mainly due to the deficient understanding of the involved mechanisms nanofluids have developed as a favorable heat transfer fluid. Recently, hybrid nanofluids were defined as a new class of nanofluids with possible applications in almost all the fields of heat transfer. This is mainly because of the synergistic effect through which they provide promising properties of all of its constituents. The augmented thermal conductivity of nanofluids over the basic heat transfer fluids (e.g. water) is considered one of the driving factors for enhanced performance in heat transfer. Nevertheless, most of the studies are discussing the thermal conductivity and only few are about viscosity variation, while other properties are neglected. The idea of using hybrid nanofluids is to further improve the heat transfer characteristics of individual nanofluids and to beneficially combine different properties from oxides, carbon nanotubes, metals, composites etc. This review summarizes most of the recent research on the preparation, thermophysical properties, correlations and heat transfer characteristics of hybrid nanofluids and compares some fully and partially described hybrids. Review showed that proper characterization may make hybrid nanofluids a very promising new heat transfer fluid. However, a lot of research work is still needed in the field of preparation and stability, characterization, and applications to overcome the barriers in implementing these new fluids in real-life applications.