Protic dialkylammonium-based ionic liquids as promising solid-solid phase change materials for thermal energy storage: Synthesis and thermo-physical characterization

Thermal behavior of phase change plates using tunnel lining GHEs for cool storage: Effect of pipe design parameters and PCM latent heat

Energy storage potential analysis of phase change material (PCM) energy storage units based on tunnel lining ground heat exchangers

What about greener phase change materials? A review on biobased phase change materials for thermal energy storage applications

Research on phase change material (PCM) for thermal energy storage is playing a significant role in energy management industry. However, some hurdles during the storage of energy have been perceived such as less thermal conductivity, leakage of PCM during phase transition, flammability, and insufficient mechanical properties. For overcoming such obstacle, researchers have been concentrating on composite PCM, where PCM is combined with metal or non-metal particles, fibrous materials, expanded or porous materials, and flame retardants. The main purpose of the current paper is to review the properties enhanced paraffin-based composite PCM. In the literature review, paraffin is selected as a thermal energy storage material, which is mixed with property-enhancing material to prepare composite. Structural and thermal properties of composite have been explored with the help of scanning electron microscope, X-ray diffractometer, transmission electron microscope, polarizing optical microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. Mechanical properties of the material are also portrayed using different testing techniques. Nevertheless, numerical methods have also been adopted for characterization of composite. It is found from the literature review that with incorporation of property-enhancing material, thermal conductivity, phase transition rate, and shape stability of PCM increased at the same time flammability, heat storage capacity, and mechanical properties reduced.

Organic Ionic Plastic Crystals (OIPCs) are increasingly drawing attention as a new type of solid-state electrolyte for lithium rechargeable batteries, because they can essentially relieve the safety concerns of the present commercial lithium batteries based on organic and flammable solvents and thus pave the way towards more robust energy storage solutions for electric vehicles and power grids. However, although significant progress has been made towards the realisation of practical OIPC-based solid electrolytes, the lack of thorough fundamental understanding of their properties, especially the nature of their ionic motion and transport and the effects of Li salt addition, has limited the development of prototype lithium cells using OIPC-based electrolytes. This PhD thesis therefore has three goals: 1) to obtain more insights into the fundamentals of the materials, especially their phase-dependent plastic crystal behaviour; 2) to under- stand the effects of the addition of Li ions on the structure and dynamics of OIPC matrices; 3) to demonstrate prototype Li cells with OIPC-based electrolytes operating at ambient temperature. For Goal 1, two recently synthesised phosphonium cation-based OIPCs, i. e. diethyl(methyl)(isobutyl)phosphonium hexafluorophosphate ([P1224][PF6]) and triethyl(methyl)phosphonium bis(fluorosulfonyl)imide ([P1222][FSI]) were investigated by a combination of analytical methods and theoretical simulations/calculations. The evolution of the motions of the cations and the anions in different phases of both plastic crystals was examined, and models proposed to explain the strongly phase-dependent ionic conductivities of these OIPCs. Cooperative motion of cations and anions was proposed for [P1222][FSI] at a particular temperature range, in which some unusual phase behaviour was observed. For Goal 2, molecular dynamics simulations of the effects of lithium salt addition to a model plastic crystal, tetramethylammonium dicyanamide ([N1111][DCA]) were performed. Cluster formation between Li ions and anions was found: Li-DCA clusters enhance the mobility of the ions that are not in the clusters. This is a somewhat surprising atomic-level explanation of how doped Li ions in the OIPC enhance its ion transport properties. For Goal 3, the electrochemical properties of triisobutyl(methyl) phosphonium bis(fluorosulfonyl) imide ([P1444][FSI]) were examined, and this plastic crystal was used to build prototypical Li metal cells. These cells showed, for the first time, practical cell performance (ca. 160 mA h g-1 discharge capacity achieved at 0.1 C) at ambient temperature. The main contributions of this thesis to the field are 1) proposing new models of the ionic motions of OIPCs with respect to their phase behaviour 2) showing the value of the combined analytical and theoretical methodology in studying OIPCs; 3) demonstrating promising Li cell performance with an OIPC-based electrolyte at ambient temperature.

Integrated power generation cycle (Kalina cycle) with auxiliary heater and PCM energy storage

Thermal conductivity enhancement of phase change materials for thermal energy storage: A review

An overview of recent literature on the micro- and nano-encapsulation of metallic phase-change materials (PCMs) is presented in this review to facilitate an understanding of the basic knowledge, selection criteria, and classification of commonly used PCMs for thermal energy storage (TES). Metals and alloys with high thermal conductivity can be used as PCMs for rapid heat storage in compact systems owing to their high volumetric TES density. The emerging application of metal PCMs in different fields such as solar thermal energy management, smart wearable devices with thermal comfort control, and cooling of electronic devices call for the need of micro- and nano-TES particles, which can be synthesised in different forms to satisfy specific requirements. As metals are easily oxidised, especially at the micro- and nano-level, encapsulation of metal-based PCM particles is important for sustainable use at high operating temperature in ambient conditions. Recent studies focusing on the encapsulation of metallic PCMs at the micro- and nano-level have been reviewed and classified in terms of the melting point of metal/alloy PCMs used and types of encapsulation materials, such as oxides, polymers, carbon, and metals. The current review is expected to provide an outlook on novel metal and alloy PCMs with function-directed structures and superior TES properties for a broad range of applications.

Paraffin wax is widely recognized as a promising phase change material (PCM) for latent heat thermal energy storage (LHTES) systems due to its high latent heat, chemical stability, and low cost. However, its inherently low thermal conductivity limits the charging and discharging rates. To overcome this limitation, nanomaterials such as graphene, with ultra-high thermal conductivity, large surface area, and excellent mechanical strength, have been integrated with paraffin wax. This paper reviews in detail the application of graphene–paraffin wax nanocomposites. Various studies have reported conductivity enhancements with minimal reduction in latent heat, demonstrating graphene’s superiority over conventional fillers. Emphasis is placed on experimental investigations, characterization techniques, and real-world applications in renewable energy, electronics cooling, and building materials. graphene–paraffin nanocomposites represent a transformative approach toward efficient thermal energy storage systems. Paraffin wax-based phase change materials (PCMs) are widely used in latent heat thermal energy storage (LHTES) due to their high energy density and chemical stability. Recent advancements demonstrate that incorporating graphene, a two-dimensional nanomaterial with ultra-high thermal conductivity and large surface area, significantly improves the heat transfer capability of paraffin wax while preserving its latent heat capacity. This paper reviews the role of graphene as a thermal conductivity enhancer in paraffin PCMs, with applications in solar thermal systems, building integration, industrial safety equipment, and electronics cooling.

Material selection and production conditions are imperative for determining the functional performances of composite materials. Phase-change composites obtained from phase-change materials (PCMs) and supporting matrices exhibit high thermal energy storage density. They are used to overcome the intermittency issues of wind and solar energy, as well as to reduce waste heat dissipation to the environment. However, the large-scale utilization of composite and pristine materials has severe drawbacks, primarily stemming from the complex fabrication routes of the encapsulating agents, leakage, and inadequate thermal stability. In this study, biochar-based phase-change composites were fabricated using vacuum infiltration techniques, and the effects of biomass feedstock and pyrolysis temperature on the performance of the composite were elucidated using different types of biowastes and temperatures. This approach has several advantages, including facile production techniques, low-cost carbon sources, and environmental friendliness. The PCM adsorption ratio of biochars derived from rice husk (RH) and Miscanthus straw linearly correlated with the pyrolysis temperature (550–700 °C), while RH700 resulted in a composite with a high enthalpy per unit mass of hexadecane (HXD) in RH700/HXD (250.9 J g−1) owing to the high surface area of RH700 (74.66 m2 g−1). The crystalline temperature increased slightly from 10.7 °C in RH550/HXD to 10.9 °C in RH700/HXD, suggesting improved molecular motion and crystal growth of HXD. Wheat straw biomass pyrolyzed at a low temperature (550 °C), displaying a reduced surface area at 700 °C (7.35 m2 g−1) and exhibiting the lowest energy storage density. The latent heat efficiency reached 99.5–100%, where RH700/HXD exhibited 100% efficiency. The composites demonstrated strong leakage resistance at high heating temperatures (60 °C, above the melting temperature of HXD), good chemical compatibility between the biochar and HXD, and high durability after 500 thermal cycles. Therefore, the extent of PCM loading and energy storage density improvements primarily depends on the pyrolysis conditions, feedstock used, and pore size distribution of the biochar samples. This research provides insights into the fabrication of phase-change composites and optimization of the carbonization process of different biomasses used for thermal management applications, such as building energy savings.Graphical

A 3D resolved-geometry model for unstructured and structured packed bed encapsulated phase change material system

Recent development on heat transfer and various applications of phase-change materials

Due to the intermittent nature of solar energy availability, storing sun’s energy in the form of latent thermal energy of a phase change material (PCM) is an effective technique that is widely used in energy storage and load management applications. In a Latent Thermal Energy Storage System (LTES), a heat transfer fluid (HTF) exchanges energy with a PCM. The advantages of an LTES include its isothermal operation and high energy storage density. However, the low thermal conductivity of PCM poses a significant disadvantage due to reduction in the rate at which the PCM can be melted (charging) or solidified (discharging). This paper explores an approach to reducing the thermal resistance of PCM in a LTES through embedded heat pipes. A heat pipe is a passive heat transfer device that efficiently transfers large amount of energy between the PCM and HTF thus indirectly amplifying the effective thermal conductivity of PCM. A transient computational analysis of a shell and tube LTES embedded with heat pipes is performed for charging to determine the position of melt front and energy stored as a function of time. The influence of the number and orientation of heat pipes and design configuration of the system is analyzed to identify configurations that lead to improved effectiveness.

The integration of thermal energy storage systems (TES) in waste-heat recovery applications shows great potential for energy efficiency improvement. In this study, a 2D mathematical model is formulated to analyze the performance of a two-tank thermochemical heat storage system using metal hydrides pair (Mg2Ni/LaNi5), for high-temperature waste heat recovery. Moreover, the system integrates a phase change material (PCM) to store and restore the heat of reaction of LaNi5. The effects of key properties of the PCM on the dynamics of the heat storage system were analyzed. Then, the TES was optimized using a genetic algorithm-based multi-objective optimization tool (NSGA-II), to maximize the power density, the energy density and storage efficiency simultaneously. The results indicate that the melting point Tm and the effective thermal conductivity of the PCM greatly affect the energy storage density and power output. For the range of melting point Tm = 30–50 °C used in this study, it was shown that a PCM with Tm = 47–49 °C leads to a maximum heat storage performance. Indeed, at that melting point narrow range, the thermodynamic driving force of reaction between metal hydrides during the heat charging and discharging processes is almost equal. The increase in the effective thermal conductivity by the addition of graphite brings about a tradeoff between increasing power output and decreasing the energy storage density. Finally, the hysteresis behavior (the difference between the melting and freezing point) only negatively impacts energy storage and power density during the heat discharging process by up to 9%. This study paves the way for the selection of PCMs for such combined thermochemical-latent heat storage systems.

Influence of PCM thermal conductivity and HTF velocity during solidification of PCM through the free cooling concept – A parametric study