•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.
•A mathematical model of the packed-bed TES with PCM capsules is established.•The PCM-TES is utilized in CSP system which is coupled with S-CO2 Brayton cycle.•Influence of melting temperature on ...performances of the cascaded PCM-TES is studied.•The thermal performances of the non-, two-, and three-cascaded PCM-TES systems are compared.•A design method for maximizing effective utilization rate of PCM is proposed.
In the concentrating solar power (CSP), the thermal energy storage system (TES) is under the constraint of the outlet threshold temperatures. Therefore optimizing the distribution of phase change materials (PCM) with different melting temperature is an effective way to improve the performance of PCM-TES. In the study, a mathematical model of the packed-bed TES system with PCM capsules is established, and the PCM-TES is under the constraint of the outlet threshold temperatures in charging and discharging processes. Based on the model, the effects of the melting temperature on the performances of the non-cascaded, two-cascaded, and three-cascaded PCM-TES are studied. The results are concluded as follows. (1) For the non-cascaded PCM-TES, the effective utilization rate of the PCM is greatly affected by the melting temperature. The maximum utilization rate is only about 40%. (2) For the two or three cascaded PCM-TES, the effective utilization rates of PCM can be greatly improved by choosing a reasonable melting temperature. (3) A design criterion of melting temperature is proposed with the goal of the maximum effective utilization rate for cascaded PCM-TES under the constraint of outlet threshold temperature in CSP. Using this proposed criterion, the effective utilization rate can reach 84%, which is about twice as high as that in non-cascaded PCM-TES. The results of optimizing the distribution of PCMs with different melting temperatures can be beneficial for the various application of the PCM-TES system which is under the constraint of outlet threshold temperature.
•A novel cooling system coupling nano emulsion and composite PCM is presented.•Effects of inlet coolant temperature and melting point are numerically studied.•The optimal operating condition for the ...hybrid cooling system is obtained.•Cooling strategy is optimized to enhance the cooling efficiency of PCM.•Tmax and ΔTmax are restrained below 48 °C and 4 °C with low power consumption.
To improve the working performance of lithium-ion batteries under long-term charge–discharge cycles, a delayed cooling system coupling composite phase change material (CPCM) and nano phase change material emulsion (NPCME) is proposed and numerically studied. In this study, optimisation of the dissipate structure was first conducted to obtain the optimal design. Subsequently, the cooling performance of a hybrid battery thermal management system (BTMS) coupling the CPCM and NPCME was comprehensively investigated. The effects of operating conditions such as inlet temperature, CPCM melting point, and NPCME melting point on the cooling performance were separately studied, and the optimal operating conditions were obtained. Finally, the thermal behaviour of the delayed cooling system was studied both in a single charge/discharge operation and continuous charge/discharge cycles. Simulation results indicated that the NPCME/CPCM system offers better cooling performance than the conventional Water/CPCM system, and the NPCME/CPCM cooling system can restrain the target ΔTmax at lower flow rates than Water/CPCM cooling. Compared with the existing hybrid cooling system, power consumption can be significantly reduced without sacrificing the cooling performance. The temperature and temperature difference of the battery pack were below 48 °C and 4 °C in three charge–discharge cycles, respectively, with a CPCM utilisation of 90 vol% and a working time of liquid cooling less than one-quarter of the cycle process.
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.
•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 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.
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.
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.
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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