Thermophysical and rheological properties of hybrid nanofluids: a review on recent studies

Hybrid nanofluids are gaining popularity due to better thermophysical properties than mono nanofluids. They also benefit from the fact that their properties can be changed by changing the type and mixture ratio of nanoparticles. The properties of mono nanofluids can be changed appreciably by varying several parameters such as nanoparticles concentration, nanoparticles diameter, nanoparticles shape, temperature, pH, surfactant, and ultrasonication time. In case of hybrid nanofluids, however, besides these parameters, nanoparticles mixture ratio and even relative diameter also affect the thermophysical and rheological properties. Recently, a good number of studies have been conducted on thermophysical and rheological properties of hybrid nanofluids. However, majority of these studies have focused on thermal conductivity, followed by viscosity and specific heat capacity. The aim of this review paper is to provide a detailed review on recently conducted studies on the thermophysical and rheological properties of hybrid nanofluids. Also, special emphasis has been placed to review the effect of nanoparticles mixture ratio on the aforementioned properties. Besides experimental determination, researchers have also relied on computational methods for modeling these properties. Therefore, several recently developed soft computing models (such as artificial neural networks, adaptive neuro-fuzzy inference system) and empirical correlations are also presented in this review paper. Lastly, in light of studies reviewed, recommendations for future work are also presented.