A review on assessment of thermal conductivity enhancement strategies for phase change materials

The increasing global energy demand and the crucial need for efficient thermal management highlight the importance of thermal energy storage (TES). Latent heat storage (LHTS) using phase change materials (PCMs) is a promising TES technology, offering high energy density and near-constant temperature operation for diverse applications like solar thermal, buildings, and battery thermal management. It supports global initiatives such as SDG-7 (affordable and clean energy) and SDG-13 (climate action) for more sustainable future. However, the widespread use of pure PCMs is significantly limited by their inherently low thermal conductivity, which hinders charging/discharging efficiency and thermal response. Therefore, this review critically discusses strategies currently employed to enhance the thermal conductivity of PCMs, with particular attention to the use of nanoparticles (forming nano-PCMs or NePCMs) and their synergy with other enhancement techniques. It examines the effects of these strategies on key thermophysical properties, performance in different applications, identifies unresolved issues, and discusses future development prospects. Major findings indicate that incorporating highly conductive nanoparticles like carbon-based materials leads to significant thermal conductivity improvements, with optimized loading. However, challenges persist, including potential reductions in latent heat capacity, increased viscosity suppressing natural convection, high cost, and critical issues like nanoparticle aggregation and separation during thermal cycling that compromise stability. Overcoming these limitations through methods like nanoparticle surface modifications, often combined with structural modifications and encapsulation, is crucial for realizing the substantial potential of PCMs in future thermal management systems.