Research progress on hybrid nanofluids for heat transfer process intensification

Owing to the rapid progress of science and technology, microelectronic devices characterized by high integration and exceptional performance have assumed crucial roles in various industrial fields such as aeronautics, astronautics, energy, medicine, and automobiles. As these devices constantly evolve, the issue of effective thermal management becomes increasingly of utmost importance, specifically in the case of high heat flux. Traditional cooling methods, such as air and liquid cooling, show notable disadvantages. They not only consume significant power but also present lower heat dissipation efficiency. These limitations considerably threaten the stability and reliability of microelectronic devices. Recently, numerous approaches to enhancing heat transfer have been proposed, encompassing both passive strategies, such as nanofluids, surface roughness, and heating element structures, and active techniques involving acoustic, electric, and magnetic fields. Among these approaches, the use of nanofluids stands out due to their inherent advantages, including cost-effectiveness, flexibility, and versatile applications. Aiming to address the low thermal conductivity of basic working fluids such as water, ethylene glycol, and mineral oil, researchers have developed a series of particulate forms including but not limited to silica dioxide (SiO₂), aluminum oxide (Al₂O₃), titanium dioxide (TiO₂), carbon nanotubes, copper (Cu), silver (Ag), silicon carbide (SiC), nanodiamond, zinc oxide (ZnO), magnesium oxide (MgO), and cupric oxide (CuO). These materials have led to nanofluids, which can be classified into mono nanofluids and hybrid nanofluids based on the particle composition. Hybrid nanofluids include at least two nanoparticle types. The unique advantages stemming from their mechanical and chemical stability, diverse structural configurations, and varied preparation techniques have significantly fascinated researchers. Currently, hybrid nanofluids present outstanding intensification performance across both single-phase and two-phase heat transfer processes. Some of them have superior performance to their mononanofluids due to the collaborative interplay of diverse nanoparticles. These characteristics enable hybrid nanofluids as promising candidates for diverse technological areas such as national defense, air-conditioner systems, semiconductors, mechanical manufacturing and materials. Combining hybrid nanofluids with heat transfer methodologies has also garnered considerable attention and is gradually evolving into a crucial direction for heat transfer improvement. In this study, we present a comprehensive overview of the research progress on enhancing the heat transfer process with hybrid nanofluids. First, the preparation techniques for hybrid nanofluids encompass both one-step and two-step methodologies, with a focus on emerging innovative approaches. Furthermore, the physical and chemical characteristics (including but not limited to stability, viscosity, and thermal performance) are reviewed. A detailed discussion of the principle of thermal enhancement is presented. Moreover, this review summarizes the applications of hybrid nanofluids in effectively managing heat within microelectronic devices, solar energy, and heat exchangers. Finally, we outline some challenges in this field and further directions for the advancements of hybrid nanofluids.