Enhancing thermal conductivity of novel ternary nitrate salt mixtures for thermal energy storage (TES) fluid

Abstract

Efficient thermal energy storage (TES) is crucial for concentrated solar power (CSP) plants, necessitating the exploration of advanced heat transfer fluids with enhanced thermal conductivity. Conventional binary nitrate salt mixtures have limitations in thermal performance, prompting research into ternary mixtures and nanoparticle additives. This study investigates novel ternary nitrate salt mixtures comprising potassium nitrate (KNO₃), lithium nitrate (LiNO₃), and magnesium nitrate hexahydrate (Mg(NO₃)₂·6 H₂O) as high-performance TES fluids during the during the heat absorption phase. Seven different salt compositions were synthesized and characterized using the laser flash technique to evaluate their thermal conductivity over 100–400°C. Results revealed a significant influence of composition on thermal conductivity, with maximum values during melting ranging from 0.0777 W/m·K to 0.7373 W/m·K. Melting points varied from 335 K to 340.39 K, demonstrating tailorability through compositional adjustments. Furthermore, incorporation of 0.5 wt% aluminum oxide (Al₂O₃) nanoparticles resulted in substantial thermal conductivity enhancements, with the most significant increase observed in TSF10 (from 0.0777 W/m·K to 0.491 W/m·K). These improvements are attributed to enhanced phonon transport, increased surface area, and Brownian motion facilitated by Al₂O₃ nanoparticles. The study provides a comprehensive cost analysis, including raw material costs, and discusses the potential efficiency gains for CSP applications. The findings contribute to the development of high-performance and cost-effective TES fluids, advancing the efficiency and viability of sustainable energy generation.