Improved effective thermal conductivity of sand bed in thermal energy storage systems

Thermal energy storage (TES) is becoming increasingly important in the modern energy landscape. As the global energy demand continues to rise and the integration of renewable energy becomes crucial, there is a growing need for sustainable and affordable ways to store energy. TES materials, such as sand, molten salts and heat transfer fluids, are a significant contributing factor to the cost-effective characteristics of TES systems. In recent advancements, sand has been viewed as a high-potential TES material for TES applications, attributed to its thermal resistance, widespread availability, safety, and affordability. However, the low thermal conductivity of sand remains a challenge for some TES applications. This study evaluates different correlations for effective thermal conductivity in a sand-based experimental study where the best correlation was adapted for a numerical simulation of the sand bed. The study further explores the use of discarded metallic chips to enhance the thermal conductivity of the sand. Our experiments assessed two integration techniques using three distinct metallic materials. It was found that the maximum heat rate could be achieved with 20 % (volumetric basis) of aluminium chips mixed in sand (1.7 times that of pure sand).