Noble Nanofluids and Their Hybrids for Heat Transfer Enrichment: A Review and Future Prospects Coverage

The novel class of fluids known by nanofluids is composed of colloidal suspensions of solid nanoparticles dispersed in a base fluid. When the solid nanoparticles are made of noble metals they can be named as noble metals nanofluids or noble nanofluids for short. This review attempts to offer a comprehensive survey along with a critical analysis of the noble metals nanofluids and their hybrids. Hence, the nanofluids having gold, silver, palladium, platinum, iridium, among others, nanoparticles are overviewed, giving emphasis to their superior thermophysical characteristics, stability, synthesis easiness, and potential applications. This work summarizes the published research findings about the noble metal nanofluids including the synthesis methods, heat transfer underlying mechanisms, and their performance evaluation in heat transfer and thermal energy storage purposes. This work intends also to provide practical insights in applications like Concentrated Solar Power systems, transformers, heat exchangers and heat pipes, cooling of electronics, among others. Also, it is highlighted the impact of the different formulations, temperature and pH values, and surfactants in the thermal conductivity, specific heat, and viscosity of these nanofluids. Besides, the interactions between the metal nanostructures and the base fluid molecules as viscosity and thermal conductivity determiners are discussed. Finally, the limitations, challenges, and prospects of the noble nanofluids are addressed such as their scalability and investment cost in large-scale applications.