Nano-enhanced phase change materials: Fundamentals and applications

Phase Change Materials (PCMs) enable thermal energy storage in the form of latent heat during phase transition. PCMs significantly improve the efficiency of solar power systems by storing excess energy, which can be used during peak demand. Likewise, they also contribute to reduced overall energy demand through passive thermal regulation. Nonetheless, thermal energy charging and discharging are restricted due to the low conducting nature of the energy storage medium. Various research investigations are being carried out to improve the thermal characteristics of PCMs through techniques such as a) dispersion of nanoparticles, b) inserting fins, and c) cascading PCMs. Among the techniques mentioned above, the dispersion of nanoparticles is reliable and economically viable. These materials are so-called nano-enhanced PCMs (NePCMs) that facilitate the charging and discharging processes of the thermal energy storage (TES) units owing to their improved thermo physical properties and long term stability. This paper presents a comprehensive review with implications and inferences on research conducted using nano-enhanced phase change materials (NePCMs) in recent years. Initially, the article discusses the highly preferred synthesis methods of NePCMs in addition to its morphological and thermophysical characterization techniques. Then, an acute focus on the impact of distinct dimensional nano additives like zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) on inclusion with PCMs are elaborately discussed. A deep discussion on emerging and hybrid nanoparticles dispersed PCMs with emphasis on a) the interaction mechanism of nanoparticle & phase change material (PCM) and b) influences on enhancing the thermophysical properties (melting point, thermal conductivity, latent heat capacity, thermal diffusivity, and thermal stability) of NePCMs are discussed. Indeed, including nanomaterials within the PCM matrix resulted in variations in thermal conductivity and heat storage enthalpy. With nanomaterial NePCM displayed 80–150 % increment in organic PCM as their proportion of nanomaterial inclusion is about 1–2 %, whereas for form and shape stable PCM enhancement of 700–900 % in thermal conductivity is noticed; however, there was a drop in heat storage enthalpy owing to the inclusion of nanomaterial in weight fraction of 5–20 %. Furthermore included in this review article are insights on significant advances, challenges, and outlooks for enhancing NePCMs in the field of advanced thermal applications. This review article is expected to have a particular reference value that would provide notable insight to readers to explore the fundamental properties of NePCM further. Additionally, as there is alarming interest in the field of TES late after the framework of sustainable development goals (SDG)s by the United Nations in 2015, this review article is anticipated to make a remarkable impact towards SDG 7-Affordable and Clean Energy, by providing technical insights towards enhancing the renewable energy sources assisted with TES.