Preparation, Characterization, Stability and Thermophysical Properties of Bio, Non-Bio (Metallic and Non-Metallic) and Hybrids Nanofluids: A Review

Traditional heat transfer base fluids, such as ethylene glycol, ethanol, kerosene, oil, methanol, water etc. are normally used to enhance the heat transfer performance in many industrial applications. These traditional heat transfer fluids have many limitations. One of the limitations is the poor thermophysical properties of each of the base fluids and this results in a lower heat transfer rate in Thermal Engineering systems. Nanofluids are considered a new generation heat transfer fluid with higher thermal conductivity. Nanofluids have enhanced thermophysical properties compared to single-phase traditional heat transfer fluids. This paper highlights detailed reviews of the various methods of preparation, characterization, stability and thermophysical properties of bio, non-bio and hybrids nanofluids. Thermophysical properties such as density, viscosity, thermal conductivity and specific heat capacity from different works of literature were summarized, discussed and presented. There are many different parameters to be considered while investigating the thermophysical properties of nanofluids. Density and specific heat capacity are strongly dependent on the material type while the viscosity and thermal conductivity are highly affected by temperature and concentration. The most influential parameters on thermophysical properties of nanofluids are material type and temperature. The majority of the literature revealed that bio nanofluids have low viscosity values and hybrids have high thermal conductivity values. The novelty of this review paper is the presentation of the various methods of synthesizing, characterization, stability and factors affecting the thermophysical properties of metallic, non-metallic and hybrid nanofluids.