Carbon-ceramic hybrid nanofluids for automotive radiators: Current status, design considerations and future directions

In the contemporary automotive industry, thermal management is critical for optimizing engine operation and enhancing energy efficiency. In situations of increasing engine load, standard radiator coolants such as water and ethylene glycol have relatively low thermal conductivity and therefore cannot cool efficiently. Nanofluids have thus taken center stage as an alternative due to their improved thermophysical properties. Carbon-ceramic hybrid nanofluids, which combine the high thermal conductivity of carbon-based nanoparticles with the mechanical strength and stability of ceramic materials, have received significant attention. This paper presents a comprehensive review of carbon-ceramic hybrid nanofluids for automotive radiators. This review discusses the basic characteristics of popular nanoparticles, such as graphene, carbon nanotubes, silicon carbide, and aluminum oxide, and their interactions in the context of improving heat-transfer performance. It also discusses relative methods for preparation, dispersion stability, and the effects of variables such as nanoparticle concentration and base-fluid composition on thermal conductivity and convective heat-transfer properties. The literature shows that hybrid nanofluids can significantly increase thermal conductivity and overall heat transfer, with a study using graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) in coolant oil reporting an Overall Heat Transfer Coefficient (OHTC) enhancement of approximately 124% in the best-performing formulations reported to date. Although all these are encouraging developments, there are still some challenges, namely increased viscosity, pressure drops, nanoparticle agglomeration, and long-term stability issues, which can impede the practical application of nanoparticles in commercial radiator systems. This review, therefore, highlights the design factors, economic viability, and system-level effects of incorporating hybrid nanofluids into automotive cooling systems. Lastly, future research directions are outlined, including the need to test under real-world conditions, improve nanoparticle stability, and explore carbon-ceramic hybrid nanofluids for next-generation thermal management systems, e.g., electric-vehicle battery cooling systems.