A Review of Hybrid Nanofluids: Emerging Trends and their Role in Enhancing Parabolic Trough Concentrators Performance

The article examines how hybrid nanofluids can significantly improve the efficiency of PTC used in solar thermal energy applications. The aim is to evaluate recent advancements in hybrid nanofluids, focusing on their thermophysical properties and their impact on PTC efficiency. The objective is to provide a comprehensive analysis of thermal, optical, and rheological characteristics, identify research gaps, and propose future directions for optimizing PTC performance. By incorporating a mixture of different nanoparticles into a single base fluid, hybrid nanofluids achieve enhanced thermal properties and more efficient heat transfer than single-particle nanofluids, achieving thermal efficiency improvements of up to 2.8% in PTCs and 197% in solar collectors. Notably, Al₂O₃/water nanofluid at 3% concentration increased thermal efficiency by 28%, from 40.8% to 52.4%. The novelty lies in integrating nanoparticle functionalization, surfactant-assisted stabilization, and passive techniques like turbulators to enhance stability and exergy efficiency. Challenges such as long-term stability, viscosity-related pressure drops, and scalability are addressed, offering insights for sustainable solar energy harnessing and green hydrogen production.