Solidification Enhancement of Thermal Energy Storage Systems Using CuO–Ethylene Glycol Nano-Enhanced Phase Change Materials: A Comprehensive Review

Abstract

Latent heat thermal energy storage (LHTES) with phase change materials (PCMs) has high energy density and near-isothermal operation; however, the low thermal conductivity of PCM is a big challenge. This review article explores the nano-enhanced phase change materials (NePCMs) with copper oxide–ethylene glycol (CuO–EG) and copper oxide–water–ethylene glycol (CuO–water–EG) and evaluates their use to enhance the solidification process in cold thermal energy storage (TES) systems. The review critically synthesizes pertinent literature on the preparation routes, dispersion stability, thermophysical properties, heat transfer mechanisms, TES configurations, hybrid strategies, numerical modeling, applications, and challenges. The results presented in the reviewed works demonstrate that CuO addition can enhance the thermal conductivity by 5–35% and decrease the solidification time by 5–25% when low to moderate CuO loading, which is usually 1–3 wt.%, is used, providing a balance of heat transfer enhancement and storage performance. But a high level of CuO concentration can lead to high viscosity, agglomeration, and settling, and low latent heat of capacity. However, for a scalable, reliable, and efficient cold TES operation and application in real systems, optimized formulation, long-term cyclic validation, and application-specific TES design are required.