•Review of organic phase change materials for thermal energy storage.•Review of the eutectic mixtures of organic PCMs.•Review of the techniques of PCM encapsulations and enhancing the thermal ...conductivity.•Applications of low and medium temperature organic PCMs are listed in detail.•Recommendations are made for future applications of organic PCMs.
Thermal energy storage as sensible or latent heat is an efficient way to conserve the waste heat and excess energy available such as solar radiation. Storage of latent heat using organic phase change materials (PCMs) offers greater energy storage density over a marginal melting and freezing temperature difference in comparison to inorganic materials. These favorable characteristics of organic PCMs make them suitable in a wide range of applications. These materials and their eutectic mixtures have been successfully tested and implemented in many domestic and commercial applications such as, building, electronic devices, refrigeration and air-conditioning, solar air/water heating, textiles, automobiles, food, and space industries.
This review focuses on three aspects: the materials, encapsulation and applications of organic PCMs, and provides an insight on the recent developments in applications of these materials. Organic PCMs have inherent characteristic of low thermal conductivity (0.15–0.35W/mK), hence, a larger surface area is required to enhance the heat transfer rate. Therefore, attention is also given to the thermal conductivity enhancement of the materials, which helps to keep the area of the system to a minimum. Besides, various available techniques for material characterization have also been discussed. It has been found that a wide range of the applications of organic PCMs in buildings and other low and medium temperature solar energy applications are in abundant use but these materials are not yet popular among space applications and virtual data storage media. In addition, it has also been observed that because of the low melting point of organic PCMs, they have not yet been explored for high temperature applications such as in power plants.
Phase‐change memory devices have found applications in in‐memory computing where the physical attributes of these devices are exploited to compute in places without the need to shuttle data between ...memory and processing units. However, nonidealities such as temporal variations in the electrical resistance have a detrimental impact on the achievable computational precision. To address this, a promising approach is projecting the phase configuration of phase change material onto some stable element within the device. Here, the projection mechanism in a prominent phase‐change memory device architecture, namely mushroom‐type phase‐change memory, is investigated. Using nanoscale projected Ge2Sb2Te5 devices, the key attributes of state‐dependent resistance, drift coefficients, and phase configurations are studied, and using them how these devices fundamentally work is understood.
Nonvolatile memory devices, which can both store and compute information are emerging building blocks for brain‐inspired and in‐memory computing. Here, the nuts and bolts of a “projected” mushroom type phase change computational device that can decouple the device's readout characteristics from the noisy properties of the phase change material are discussed.
The increasing growth of powerful and sophisticated electronic devices have an urgent need for excellent heat dissipation and electromagnetic interference shielding materials. However, few studies ...are focusing on one material with these properties. In this work, a novel hierarchically porous wood-derived carbon scaffold embedded phase change material was prepared via facile pyrolysis and vacuum infiltration process. Notably, the raw wood was pretreated by a delignification strategy, which makes great contributions to forming a hierarchically porous network and expanding the internal area after pyrolyzing. The results demonstrate that the honeycomb-like structure of the wood carbon scaffold was well maintained after calcination, which can provide a great number of channels for energy transmission and multi-reflection of electromagnetic waves. Moreover, the paraffin wax component as phase change material not only stores and releases numerous energies during the melting and solidification processes, but also endows the composite outstanding self-cleaning function. The present composite shows excellent energy storage property (the latent heat of 122.25 J/g) and satisfied electromagnetic interference shielding performance (average shielding effectiveness of 24.4 dB). Therefore, the synthesized porous wood carbon scaffold/paraffin wax composite has great potential in multifunctional, environmentally friendly thermal energy management and electromagnetic interference shielding applications.
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•A novel wood carbon scaffold/PW composite was prepared by facile delignifying, annealing and infiltrating processes.•The carbon based composite showed excellent thermal energy management performance.•The carbon based composite possessed high electromagnetic interference shielding effectiveness of 24.4 dB.•The multifunctional composite exhibited the merits of low-cost, environmental friendliness, and self-cleaning.
Phase‐change materials (PCMs) offer tremendous potential to store thermal energy during reversible phase transitions for state‐of‐the‐art applications. The practicality of these materials is ...adversely restricted by volume expansion, phase segregation, and leakage problems associated with conventional solid‐liquid PCMs. Solid–solid PCMs, as promising alternatives to solid–liquid PCMs, are gaining much attention toward practical thermal‐energy storage (TES) owing to their inimitable advantages such as solid‐state processing, negligible volume change during phase transition, no contamination, and long cyclic life. Herein, the aim is to provide a holistic analysis of solid–solid PCMs suitable for thermal‐energy harvesting, storage, and utilization. The developing strategies of solid–solid PCMs are presented and then the structure–property relationship is discussed, followed by potential applications. Finally, an outlook discussion with momentous challenges and future directions is presented. Hopefully, this review will provide a guideline to the scientific community to develop high‐performance solid–solid PCMs for advanced TES applications.
An holistic analysis on the recent developments of solid‐state phase‐change materials (PCMs) for innovative thermal‐energy storage (TES) applications. The phase‐transition fundamentals of solid‐to‐solid (S–S) PCMs are introduced and discussed, developing strategies and molecular engineering design toward potential applications. The current challenges and future research directions on S–S PCMs in TES applications are also proposed.
A 2D map is created for solid‐state materials based on a quantum‐mechanical description of electron sharing and electron transfer. This map intuitively identifies the fundamental nature of ionic, ...metallic, and covalent bonding in a range of elements and binary compounds; furthermore, it highlights a distinct region for a mechanism recently termed “metavalent” bonding. Then, it is shown how this materials map can be extended in the third dimension by including physical properties of application interest. Finally, it is shown how the map coordinates yield new insight into the nature of the Peierls distortion in phase‐change materials and thermoelectrics. These findings and conceptual approaches provide a novel avenue to tailor material properties.
A 2D map, based on quantum‐mechanical indicators for electron sharing and transfer, intuitively classifies the fundamental bonding mechanisms in solid‐state materials. It also confirms metavalent bonding as one of the fundamental mechanisms. Extending this map in the third dimension makes it possible to include properties of application interest, and it can therefore open up a new route for computational materials design.
•The heat transfer of NEPCM-water suspension in a parallel microchannel investigated.•The presence of NECPM-particles improves heat transfer by up to 70%.•Using NEPCMs could improve the index of ...performance by up to 45%.•NEPCM particles at high Reynolds numbers reduced the heat transfer rate.
In the present experimental study, Nano-Encapsulated Phase Change Material (NEPCM) nanoparticles with particle sizes in the range of 250–350 nm are synthesized. The core of nanoparticles is made of eicosane and can undergo liquid-solid phase change by absorbing/releasing latent heat. The eicosane core of the NEPCM particles is enclosed in a formaldehyde shell, and the particles are suspended in the water as the base fluid. The synthesized NEPCM-water suspension is employed as the working-fluid for heat removal from a microchannel heatsink. The heatsink is made of red-copper, and it consists of eight rectangular microchannels with an aspect ratio of 1.5 and a hydraulic diameter of 1.2 mm. Under the heatsink, a heating plate is embedded, which produces a uniform heat flux. The working-fluid, NEPCM-water, enters the microchannel and absorbs the heat from the microchannel walls in the form of sensible and latent heat. The impact of the nanoparticle's concentration, the heating-power, and the flow rate is investigated on the channel wall temperature, Nusselt number, convection ratio, performance index, and coefficient of performance. The results show that the presence of NECPM-particles improves heat transfer and the index of performance up to 70% and 45%, respectively. The observed enhancement of heat transfer is particularly notable at low Reynolds numbers. However, at the high Reynolds numbers, the presence of NECPM particles may reduce the convection ratio and performance index, which is mainly due to the increase of the viscosity and reduction of the sensible heat of the working-fluid in the presence of NEPCM nanoparticles.
Phase change materials (PCMs) possess very high heat storage capacity and are capable of maintaining a constant temperature during phase change, which makes them most prominent candidates for solar ...energy storage systems, heating, and cooling systems. The low thermal conductivity of PCM results in slow heat transfer and low heat storage and release rate, which is a major drawback for their practical applications. This review focuses on the enhancement of thermal conductivity by the introduction of highly thermally conductive metallic and carbon-based nanoparticles, metallic foams, expanded graphite and encapsulation of PCM. Carbon-based nanoparticles including carbon fiber, carbon nanotubes, and graphene show better performance than metal-based nanoparticles due to lower density and better dispersion. The thermal conductivity of the composite phase change material (CPCM) depends on the shape, size, aspect ratio and concentration of nanoparticles. The thermal conductivity of CPCM increases by increasing concentration and aspect ratio of the additive. Metallic foam and expanded graphite possess high thermal conductivity and good thermo-physical properties and also prevent leakage of PCM during phase change. The porosity of foam has a huge impact on thermal conductivity than pore size. Encapsulated PCM has well-enhanced thermal conductivity and long-lifetime due to the high thermal conductive shell which also protects the PCM from direct contact with the environment.
Wearable devices and systems demand multifunctional units with intelligent and integrative functions. Smart fibers with response to external stimuli, such as electrical, thermal, and photonic ...signals, etc., as well as offering energy storage/conversion are essential units for wearable electronics, but still remain great challenges. Herein, flexible, strong, and self‐cleaning graphene‐aerogel composite fibers, with tunable functions of thermal conversion and storage under multistimuli, are fabricated. The fibers made from porous graphene aerogel/organic phase‐change materials coated with hydrophobic fluorocarbon resin render a wide range of phase transition temperature and enthalpy (0–186 J g−1). The strong and compliant fibers are twisted into yarn and woven into fabrics, showing a self‐clean superhydrophobic surface and excellent multiple responsive properties to external stimuli (electron/photon/thermal) together with reversible energy storage and conversion. Such aerogel‐directed smart fibers promise for broad applications in the next‐generation of wearable systems.
A variety of multiresponsive smart fibers with a wide range of tunable phase transition temperatures and enthalpy are produced through impregnation of different types of organic phase‐change materials into graphene aerogel fibers and finished by coating a fluorocarbon resin layer, showing a self‐cleaning superhydrophobic surface and excellent multiple‐responsive properties to external stimuli (electron/photon/thermal) together with reversible energy storage and conversion.
This experimental study covers the chemical, physical, thermal characterization and application of novel nanocomposite phase change materials (NCPCMs) dispersed by TiO2, Al2O3, and CuO nanoparticles ...for thermal management systems. A commercial-grade of paraffin, namely RT-35HC, was considered as a phase change material (PCM). The mono and hybrid NCPCMs were synthesized at a constant weight concentration of 1.0 wt.%. In the first phase, various characterization techniques were used to explore the thermophysical properties and chemical interaction of mono and hybrid NCPCMs. In the second phase, the thermal cooling performance was investigated by filling the prepared NCPCMs in a heat sink at various input power levels. The results showed the uniform dispersion of TiO2, Al2O3, and CuO nanoparticles onto the surface of both mono and hybrid NCPCMs without altering the chemical structure of RT-35HC. The optimum latent-heat of fusion and highest thermal conductivity of 228.46 J/g and 0.328 W/m K were obtained, respectively, of Al2O3+CuO dispersed hybrid NCPCM compared to pure RT-35HC. In comparison of RT-35HC, the increasing trend in specific heat capacity was observed of NCPCMs and 36.47% enhancement was obtained for hybrid NCPCM in solid-phase. The reduction in heat sink base temperature was achieved of 3.67%, 6.13%, 13.95% and 8.23% for NCPCMTiO2, NCPCMAl2O3, NCPCMCuO and NCPCMAl2O3+CuO, respectively, compared to RT-35HC. Further, no phase segregation, less subcooling, smaller phase transition temperature, higher chemical and thermal stability were observed with hybrid NCPCMs which can be used potentially for thermal management of electronic devices, Li-ion batteries and photovoltaic (PV) modules systems.
•Synthesized the nanocomposite PCMs by dispersing TiO2, Al2O3 and CuO nanoparticles.•Characterized the physical, chemical, and thermal properties.•Hybrid of Al2O3+CuO showed the 53.7% higher thermal conductivity enhancement.•Improved thermal and chemical stability were observed in nanocomposite PCMs.•Better cooling performance was observed with hybrid Al2O3+CuO nanocomposite PCM.
Two-dimensional transition-metal carbides/carbonitrides (MXenes) have demonstrated wide application prospect in energy conversion and storage, mostly in the form of electrochemical energy storage. ...Compared with the conversion between chemical energy and electrical energy, an energy conversion process initiated by solar energy and driven by the physical change of energy materials will be a sustainable and environmentally friendly strategy. Therefore, a high-performance MXene aerogel-based phase change material for solar energy conversion and thermal energy storage is constructed. MXene nanosheets with an extinction coefficient of 25.67 L/(g.cm) at 808 nm demonstrate excellent light absorption performance, which can spontaneously convert the solar energy into thermal energy. The polyethylene glycol (PEG) possessing high affinity with MXene acts the medium for thermal energy storage and release in the process of fusion and solidification. The MXene@PEG aerogels are lightweight, with a density about 30 mg/cm3. The MXene skeleton is introduced as supporting materials to keep the shape of MXene@PEG aerogel stable during the phase change process. The MXene nanosheets improve the thermal stability of PEG, the thermal decomposition temperatures can be increased by 40 °C. The actual fusion and solidification enthalpies of MXene@PEG aerogels can reach 167.72 and 141.51 J/g, respectively. The photothermal storage efficiency of MXene@PEG aerogels reaches a relatively high value of 92.5%. This work provides a new type of scaffold for lightweight and shape-stable photothermal carrier and paves the way for the application of non-graphene 2D materials toward solar energy utilization.
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•A brand new concept of MXene aerogel-based phase change materials for solar energy conversion has been established.•The MXene aerogel-based phase change materials are lightweight and shape-stable.•The photothermal storage efficiency of Mxene@PEG aerogels reaches 92.5%.
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