Thermal Conductivity Enhancement of Ternary Organic Heat Transfer Fluids Doped with Al₂O₃ Nanoparticles for Solar Thermal Energy Storage

Abstract

Thermal Energy Storage (TES) systems are essential for mitigating the intermittency of renewable energy, particularly in Concentrated Solar Power (CSP) applications. This study explores the enhancement of thermal conductivity in novel ternary organic-based TES fluids, composed of varying ratios of oregano oil, olive oil, and castor oil, doped with 5 wt% Al₂O₃ nanoparticles. Using differential scanning calorimetry (DSC), seven undoped formulations were characterized, followed by nanoparticle doping in three selected samples. Thermal conductivity was measured over the range of 300–400 K, yielding values from 0.2886 to 0.5233 W/m·K for undoped samples, with melting points between 333.48 K and 336.21 K. Upon doping, sample SO5 exhibited a 3.7% increase in thermal conductivity, whereas SO2 and SO7 showed decreases of 33.5% and 4.0%, respectively. These results highlight the critical influence of fluid composition, nanoparticle dispersion, and interfacial compatibility on TES performance. This work contributes to the development of cost-effective, high-efficiency TES fluids, offering new pathways for improving the sustainability and performance of CSP systems.