A wide range of heat transfer systems require efficient heat transfer management from source to sink and vice versa. Over the last decade, graphene nanoparticles, matrix nanofluids have been one of the most investigated nanoparticles for a wide range of engineering applications. Graphene-based nanoparticles have several advantages over other nanoparticles: high stability, high thermal conductivity, low erosion and corrosion, and higher carrier mobility. Graphene-based nanofluids have found applications such as heat transfer, defect sensor, anti-infection therapy, energy harvesting systems, biomedical and cosmetics. With advancement of technology, more compact and efficient cooling media are needed to ensure efficiency and reliability of engineering systems and devices. This research study reports an overview of experimental and numerical investigations of graphene nanometer-sized particles with different base host fluids for major engineering applications of energy transfer systems and further thermophysical properties of graphene nanofluids.

In this paper, the fundamental overview of theoretical and practical aspects of thermodynamics analysis for mainly used fuel cells (FCs) are presented. The FC converts the chemical energy of fuel (normally hydrogen) directly into electrical energy resulting heat and liquid water as a waste products. In first part, governing equation of mass, energy, entropy and exergy are presented according to first law of thermodynamics (FLT) and second law of thermodynamics (SLT), more specifically energy and exergy analysis are covered for fuel cell system. Basic criteria of energy and exergy analysis of flowing and non-flowing system, energy and exergy efficiencies, analysis procedure and models of reference environment are discussed in detail. In the second part, electrochemical reactions and thermodynamics modeling of proton exchange membrane or polymer electrolyte membrane fuel cell (PEMFC), solid oxide fuel cell (SOFC), and molten carbonate fuel cell (MCFC) are presented.

Summary With advancement in technology—nanotechnology, various thermal energy storage (TES) materials have been invented and modified with promising thermal transport properties. Solid‐liquid phase change materials (PCMs) have been extensively used as TES materials for various energy applications due to their highly favourable thermal properties. The class of PCMs, organic phase change materials (OPCMs), has more potential and advantages over inorganic phase change materials (IPCMs), having high phase change enthalpy. However, OPCMs possess low thermal conductivity as well as density and suffer leakage during the melting phase. The encapsulation technologies (ie, micro and nano) of PCMs, with organic and inorganic materials, have a tendency to enhance the thermal conductivity, effective heat transfer, and leakage issues as TES materials. The encapsulation of PCMs involves several technologies to develop at both micro and nano levels, called micro‐encapsulated PCMs (micro‐PCM) and nano‐encapsulated PCMs (nano‐PCM), respectively. This study covers a wide range of preparation methods, thermal and morphological characteristics, stability, applications, and future perspective of micro‐/nano‐PCMs as TES materials. The potential applications, such as solar‐to‐thermal and electrical‐to‐thermal conversions, thermal management, building, textile, foam, medical industry of micro‐ and nano‐PCMs, are reviewed critically. Finally, this review paper highlights the emerging future research paths of micro‐/nano‐PCMs for thermal energy storage.

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