A critical review on synthesis and application aspect of venturing the thermophysical properties of hybrid nanofluid for enhanced heat transfer processes

Recently, nanofluids (NFs) have gathered significant attention among researchers due to their varied properties, which can be made per the requirements. NFs, created by infusing nanoparticles into a base-fluid, enhance their fundamental properties. A hybrid nanofluid (HNF) is a nanofluid (NF) containing different types of nanoparticles, and it is being studied for its customizable properties. Recently, researchers delved into the applications regarding HNFs, particularly in cases relating to heat transfer (HT). This study analyzes HNFs' preparation methods and thermophysical properties, giving more importance to their applications in HT, including heat- exchange, solar thermal, and cooling systems. Considering stability, the two-step synthesis method is preferred over the single-step method. Multiple research efforts have led to the development of a fluid that possesses superior HT capabilities compared to the base-fluid. However, while bettering HT, an increase in volume concentration (VC) also raised challenges such as increased viscosity and pressure drop, particularly in porous media, necessitating additional pumping power. The use of turbulators and other configurations, along with HNF in systems like parabolic trough solar collectors (PTSCs), enhances solar thermal systems (STSs) by improving their HT capabilities. An advantageous use of EG-based multiwalled carbon nanotubes (MWCNTs) NF in solar collectors (SCs) is their ability to increase thermal efficiency and decrease carbon dioxide emissions, making them an attractive choice for use in SCs. Researchers face significant challenges in determining the ideal composition and concentration of nanoparticles in HNFs to attain optimal HT without causing excessive viscosity that could impede practical usability. Specifically, this study examines the distinctive thermophysical characteristics of HNFs that substantially improve their efficacy in HT applications.