Spatiotemporal Utilization of Latent Heat in Erythritol-based Phase Change Materials as Solar Thermal Fuels

Solar thermal fuels (STFs) have been particularly concerned as sustainable future energy due to their impressive ability to store solar energy in chemical bonds and controllably release thermal energy. However, currently studied STFs mainly focus on molecule-based materials with high photochemical activity, toxicity, and compromised features, which greatly restricts their applications in practical scenarios of solar energy utilization. Herein, we present a novel erythritol-based composite phase change material (PCM) as a new type of STFs with an outstanding capability to store solar energy as latent heat in its stable supercooling state and release thermal energy as needed. This composite PCM with stored thermal energy can be maintained stably at room temperature and subsequently release latent heat as high as 224.9 J/g during the crystallization process triggered by thermal stimuli. Remarkably, solar energy can be converted into latent heat stored in the composite PCM over months. Through mechanical stimulations, the released latent heat can increase the temperature of the composite up to 91 °C. This work presents a new concept of using spatiotemporal storage and release of latent heat in PCMs for solar energy utilization, making it a potential candidate as STFs for developing future clean energy techniques.     

Application of PCM thermal energy storage system to reduce building energy consumption

The building sector is known to make a large contribution to total energy consumption and CO₂ emissions. Phase change materials (PCMs) have been considered for thermal energy storage (TES) in buildings. They can balance out the discrepancies between energy demand and energy supply, which are temporally out of phase. However, traditional PCMs need special latent storage devices or containers to encapsulate the PCM, in order to store and release the latent heat of the PCM. The proper design of TES systems using a PCM requires quantitative information and knowledge about the heat transfer and phase change processes in the PCM. In Korea, radiant floor heating systems, which have traditionally been used in residential buildings, consume approximately 55% of the total residential building energy consumption in heating. This article reviews the development of available latent heat thermal energy storage technologies and discusses PCM application methods for residential building using radiant floor heating systems with the goal of reducing energy consumption.     

Study on thermal properties of organic ester phase-change material embedded with silver nanoparticles

This study investigates the thermal properties of new silver nano-based organic ester (SNOE) phase-change material (PCM) in terms of latent heat capacity, thermal conductivity and heat storage and release capabilities experimentally. Spherical-shaped surface-functionalized crystalline silver nanoparticles (AgNP) prepared were embedded in mass proportions of 0.1 through 5.0 wt% into the pure (base) PCM. Experimental results reveal that dispersion of AgNP into PCM was effective, only physical and no chemical interaction between AgNP and PCM has been exhibited; thereby phase-change temperature of SNOE PCMs were acceptable. These are essential characteristics for SNOE PCMs which signified their thermal and chemical stability on long term. Test results suggest that while compared to pure PCM, degree of supercooling was reduced by 11.7–6.8 % for aforesaid mass proportions of AgNP, whereas latent heat capacities decreased by 7.88 % in freezing and 8.91 % in melting. The interdependencies between thermophysical properties in improving nucleation and growth rate of stable SNOE PCM crystals were signified and discussed. Thermal conductivity of SNOE PCMs were enhanced from 0.284 to 0.765 W m^?1 K^?1 which was expected to be a 10–67 % increase for the above mass loading of AgNP. Furthermore, for SNOE PCMs enhancement span in freezing and melting cycles was improved by 41 and 45.6 %, respectively. Similarly, cooling and melting times were reduced by 30.8 and 11.3 %, respectively. Embedded AgNP helps to achieve improved thermophysical and heat storage characteristics for SNOE PCMs, which in turn can be considered as a potential candidate for cool thermal energy storage applications.     

One-step synthesis of CuS-decorated MWCNTs/paraffin composite phase change materials and their light–heat conversion performance

Paraffin wax (PW) is a solid–liquid organic phase change material (PCM). However, the low thermal conductivity and poor light–heat conversion performance limit its feasibility in solar thermal storage applications. In this paper, CuS-decorated carboxyl multi-wall carbon nanotubes (MWCNTs)/PW light–heat conversion composite PCMs were prepared by one step. The structure and properties of the composite PCMs were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, differential scanning calorimeter, thermogravimetric analysis, coefficient of thermal conductivity, UV–visible–near infrared spectrometer and light–heat conversion testing. The results showed that the light–heat conversion performance of CuS–MWCNTs/PW composite PCMs were better than that of MWCNT/PW composite PCMs with the same mass fraction. Therefore, it is expected that this research will open up new avenues of study for the creation of advanced composite PCM with excellent light–heat conversion performance.     

Latent heat nano composite building materials

Heat storage for heating and cooling of buildings reduces the conventional energy consumption with a direct impact on CO₂ emissions. The goal of this study was to find the physico-chemical fundamentals for tailoring phase change material (PCM)-epoxy composites as building materials depending on phase change temperature and latent heat using the optimal geometry for each application. Thus, some nano-composite materials were prepared by mixing a PCM with large latent heats with epoxy resin and Al powder. Some polyethylene glycols of different molecular weights (1000, 1500, and 2000) were used as PCMs. Subsequently these PCM-epoxy composites were thermo-physically characterized by DSC measurements and found to be suitable for building applications due to their large latent heat, appropriate phase change temperature and good performance stability. Moreover these cross-linked three dimensional structures are able to reduce the space and costs for encapsulation.     

高结构稳定性、低泄漏率三维铜@石墨烯复合相变材料的制备

由于能源消费需求的持续增长和传统化学燃料的日益枯竭,对可再生能源的需求日益迫切。以地热能、太阳能为代表的可再生能源脱颖而出。然而,这些能源的应用易受到天气、季节、地点和时间的影响,具有不稳定性、随机性、波动性和间歇性。储能技术是解决上述问题的有效途径,它可以在需要的时候储存或释放能量。在各种储能技术可选材料中,相变材料(PCMs)是智能热能管理和便携式热能领域的有力候选者。大多数相变材料都存在导热系数低、环境污染、熔点泄漏等问题,因此有必要将相变材料封装到支撑骨架材料中。事实上,支撑材料在应用中仍面临着一些重大挑战。首先,骨架材料应能抵抗相变材料在相变过程中的体积变化,即具有良好的结构稳定性。其次,还应具有较高的导热系数和较低的泄漏率。石墨烯气凝胶(GA)已被证明是提高相变材料形状稳定性的有效支撑骨架,但相变引起的泄漏和网络结构的脆性是制约其应用的关键问题。在此,我们提出了一种双脉冲电镀的强化策略,用于制备铜@石墨烯气凝胶(Cu@GA)作为相变储能骨架材料。这一结构设计中,石墨烯气凝胶上的石墨烯片层上均匀地镀上了铜层,且不同片之间被铜镀层所连接。这种铜增强石墨烯气凝胶网络结构赋予复合材料良好的导热性和坚固的骨架稳定性,有利于增强相变换热和抑制相变过程中的泄漏。此外,通过真空浸渍法将十八胺(ODA)封装在Cu@GA骨架中,获得了结构稳定性高、泄漏率低的复合相变材料(Cu@GA/ODA),保证了ODA在Cu@GA骨架材料中的均匀分散和填充。通过比较复合相变材料的重量变化,研究了不同骨架对复合相变材料泄漏率的影响。优化后的复合相变材料(CPCM)Cu@GA/ODA经20次储热、放热循环后,泄漏率降低至19.82% (w,质量分数),而GA/ODA和GOA/ODA为骨架的复合相变材料的泄漏率分别为80.31% (w)和72.99% (w)。为了探讨这种影响的原因,用扫描电子显微镜(SEM)观察了循环后骨架的形貌。铜/石墨烯气凝胶(Cu@GA)骨架材料没有明显的收缩或坍塌,仍可以保持完整的三维网络结构,而氧化石墨烯气凝胶(GOA)和石墨烯气凝胶(GA)的骨架材料三维结构不复存在,且在氧化石墨烯/石墨烯片能够观察到明显的裂隙。铜涂层可以提高骨架的微观结构稳定性,有利于提高结构稳定性,降低复合材料的泄漏率。同时,该研究为构建理想的金属增强石墨烯气凝胶复合骨架材料铺平了新的道路,该复合材料具有优异的综合性能,可用于未来的相变储能、多孔微波吸收和储能应用。     

Emerging Applications of Phase‐Change Materials (PCMs): Teaching an Old Dog New Tricks

The nebulous term phase‐change material (PCM) simply refers to any substance that has a large heat of fusion and a sharp melting point. PCMs have been used for many years in commercial applications, mainly for heat management purposes. However, these fascinating materials have recently been rediscovered and applied to a broad range of technologies, such as smart drug delivery, information storage, barcoding, and detection. With the hope of kindling interest in this incredibly versatile range of materials, this Review presents an array of aspects related to the compositions, preparations, and emerging applications of PCMs.     

Evaluation of PCM/diatomite composites using exfoliated graphite nanoplatelets (xGnP) to improve thermal properties

This paper deals with the thermal performances of shape-stabilized phase change materials (SSPCM) for energy saving in various fields. This study enhanced thermal properties of SSPCM using exfoliated graphite nanoplatelets (xGnP). SSPCM, which contains the xGnP, was prepared by mixing and melting techniques for high dispersibility, thermal conductivity, and latent heat storage. In the experiment, we used hexadecane, octadecane, and paraffin as phase change materials (PCMs), and they have 254.7, 247.6, and 144.6 J g^?1 of latent heat capacity, and melting points of 20.84, 30.4, and 57.09 °C, respectively. The characteristics of SSPCMs were determined using SEM, DSC, FTIR, TG, TCi, and Energy simulation. SEM morphology showed homogenous dispersion of PCM and xGnP in the porous diatomite. DSC analysis results showed the latent heat capacity of SSPCM and SSPCM/xGnP composites, and TG analysis results showed the thermal reliability of the samples. Also, we checked the thermal conductivity of the SSPCM that contains xGnP, by TCi analysis.     

Thermodynamic insights into n-alkanes phase change materials for thermal energy storage

n-Alkanes have been widely used as phase change materials (PCMs) for thermal energy storage applications because of their exceptional phase transition performance, high chemical stability, long term cyclic stability and non-toxicity. However, the thermodynamic properties, especially heat capacity, of n-alkanes have rarely been comprehensively investigated in a wide temperature range, which would be insufficient for design and utilization of n-alkanes-based thermal energy storage techniques. In this study, the thermal properties of n-alkanes (C₁₈H₃₈-C₂₂H₄₆), such as thermal stability, thermal conductivity, phase transition temperature and enthalpy were systematically studied by different thermal analysis and calorimetry methods, and compared with previous results. Thermodynamic property of these n-alkanes was studied in a wide temperature range from 1.9 K to 370 K using a combined relaxation (Physical Property Measurement System, PPMS), differential scanning and adiabatic calorimetry method, and the corresponding thermodynamic functions, such as entropy and enthalpy, were calculated based on the heat capacity curve fitting. Most importantly, the heat capacities and related thermodynamic functions of n-heneicosane and n-docosane were reported for the first time in this work, as far as we know. This research work would provide accurate and reliable thermodynamic properties for further study of n-alkanes-based PCMs for thermal energy storage applications.     

The investigation of thermal conductivity and energy storage properties of graphite/paraffin composites

Phase change materials (PCM) have been extensively scrutinized for their widely application in thermal energy storage (TES). Paraffin was considered to be one of the most prospective PCMs with perfect properties. However, lower thermal conductivity hinders the further application. In this letter, we experimentally investigate the thermal conductivity and energy storage of composites consisting of paraffin and micron-size graphite flakes (MSGFs). The results strongly suggested that the thermal conductivity enhances enormously with increasing the mass fraction of the MSGFs. The formation of heat flow network is the key factor for high thermal conductivity in this case. Meanwhile, compared to that of the thermal conductivity, the latent heat capacity, the melting temperature, and the freezing temperature of the composites present negligible change with increasing the concentration of the MSGFs. The paraffin-based composites have great potential for energy storage application with optimal fraction of the MSGFs.     

相变蓄热材料研究进展

相变蓄热材料(恒温潜热热能储存材料)是目前最热门的功能材料之一。它在发生相变时储存、放出的热量能够帮助所在系统进行能量的储存,同时可以一定程度上缓解双方在时间、强度及地点上的不匹配程度。相变蓄热材料优点突出,其中包括在使用过程中自身温度变化较小、有很好的稳定性、储热能力较强等。此类材料对环境友好,响应了国家近年来节能环保的政策,同时也可以极大地优化所在系统的运行效率。本文综述了近年来几类相变蓄热材料的种类、特点及国内外学者应对于不同缺陷做出的改进及其应用于行业的研究现状,并对未来的发展进行了探讨与展望。     

Effect of phase change materials on the hydration reaction and kinetic of PCM-mortars

The phase change materials are considered an attractive way to reduce energy consumption thanks to their heat storage capacity. Their incorporation in the construction materials allows the energy to be an integral part of the building structure. Even though PCMs have shown their reliability from a thermal point of view, some drawbacks linked to their use were emphasized such as the loss of the compressive strength of the PCM-material. This paper attempts to provide an explanation by the investigation of the hydration kinetic of PCM-mortars. The semi-adiabatic Langavant test was adapted to this case. The numerical diffuse element method was used for the computation of the heat flux, which is a compulsory step for the determination of the hydration degree. The results showed a lower heat released by the PCM mortars compared to a control mortar as well as a delay in the hydration progress with the addition of PCMs.     

Thermal performance and flammability of phase change material for medium and elevated temperatures for textile application

Thermal energy storage and insulation have potential applications in many fields such as incorporating phase change material (PCM) in textile materials for insulation in medium and elevated temperatures when the high heat flux 80–84 kW m^?2 results from flashover conditions in a firefighting environment. The feasibility of four selected PCMs is considered in this research. The lack of guidance of hazards of sugar alcohols as a potential PCM is analyzed from molecular structure point of view. The results showed that isomerism of PCMs has a tremendous influence on the flash point of PCMs and hence flammability. Differential scanning calorimeter thermal performance showed that the four candidate PCMs have a remarkable melting temperature and enthalpy of fusion. Different heating rates were observed (1.11, 0.43, and 0.095 %) in the melting temperatures: at 50, 20, and 5 °C·min^?1, respectively. Smaller heating rates are preferable for accurate data. PCMs also undergo degradation due to the high-temperature exposure. Although dulcitol and d-mannitol have the same molecular formula, dulcitol requires higher temperature for degradation than does d-mannitol, and this difference is around 26.08 K. The analysis of results showed that the position of functional group has tremendous influence on the thermal performance. Salt hydrates have a multistep thermal degradation and the lowest loss of mass compared with sugar alcohols. This is because salt hydrates have higher intermolecular forces, which make them undergo high thermal endothermic and exothermic processes.     

聚乙二醇/二醋酸纤维素相变材料的组成与储能性能间的关系

以刚性的二醋酸纤维素 (CDA)链为骨架 ,接枝上聚乙二醇 (PEG)柔性链段 ,可得到一种具有固固相变性能的网状储能材料 .利用该材料的PEG支链从结晶态到无定形态间的相转变 ,可以实现储能和释能的目的 .具体研究了PEG的百分含量及PEG的分子量对材料储能性能的影响 .研究结果表明 ,通过改变PEG的百分含量与PEG的分子量 ,可以得到不同相变焓和不同相变温度的材料     

A Review on Polymeric-Based Phase Change Material for Thermo-Regulating Fabric Application

Abstract

Phase Changing Materials (PCM) portrays proficiency to liberate perceptible amount of latent heat on the course of phase transformation between liquid-solid or solid-liquid, thereby creating momentary warmth or cooling effect. PCM has been utilized in garments for introducing thermoregulating effect to diminish thermal discomfort of clothing. Assimilation of thermal energy by PCM causes delay in upsurge of microclimate temperature and results in substantial diminution of moisture release from skin thereby leading to inhibition of heat stress conditions and enhancement of thermo-physiological wearing comfort. Simultaneously, the insulating characteristic of such garment can also avert wearer from certain pivotal corollaries like hypothermia or heat syncope, keeping the individual in consolation owing to their automatic acclimatizing attribute in accordance with body and ecological temperature. As the assimilation of PCM into various textile materials have been extensively studied by researchers, an attempt has been made to explicate the recent existing literatures that have successfully integrated and implemented PCM in textile, concentrating on characteristics of PCMs integrated into fibers, and fabrics for potential industrial applications. Finally, various methodologies like coating, spinning & lamination being utilized for applying PCMs onto textiles for developing thermoregulated clothing have been discussed & concludes with challenges & future prospects.     

Crystallisation, melting, recrystallisation and polymorphism of n-eicosane for application as a phase change material

Phase change materials (PCM) provide thermoregulation originating from the latent heat exchanged during melting or crystallisation. Linear hydrocarbons have weak interactions, but high symmetry, providing an effective quantity of latent heat over the most acceptable temperature range for applications. The ability to both melt and crystallise over a narrow range is made complex by nucleation, polymorphism and the kinetic nature of these changes. Differential scanning calorimetry (DSC), optical microscopy and temperature modulated DSC (TMDSC) was used to study the melting of n-eicosane. This PCM has a low degree of supercooling and conversion to the most stable crystalline state (triclinic) that occurs rapidly from a metastable phase (rotator) state on cooling. TMDSC revealed a small, yet similar degree of thermodynamic reversibility in the melting of each of the crystalline phases.     

Preparation,characterization, and thermal properties of microPCMs containing <Emphasis Type="Italic">n</Emphasis>-dodecanol by using different types of styrene-maleic anhydride as emulsifier

Microcapsules containing polar phase change material (PCM) n-dodecanol were synthesized by in situ polymerization using melamine-formaldehyde resin as shell and styrene-maleic anhydride copolymer (SMA) as emulsifier. The effects of polarity of PCM and types and amounts of SMA emulsifier on the properties of microencapsulated PCMs (microPCMs) were studied and characterized by using Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and laser particle diameter analyzer. The results show that thermal properties of microPCMs are affected greatly by the types and amounts of SMA. Anionic SMA emulsifier is suitable for the encapsulation of n-dodecanol. The polarity of PCM leads to the higher adding amount of SMA emulsifier. When mass ratio of emulsifier to n-dodecanol is 4.8%, the phase change latent heat and encapsulation efficiency reach to the maximum value of 187.5 J/g and 93.1%, respectively. Irregular spherical microPCMs with mean diameter of 30.6 μm and phase change temperature of 21.5 °C are obtained and can be used for energy storage.     

Preparation and thermal properties of palmitic acid/polyaniline/copper nanowires form-stable phase change materials

Form-stable phase change materials (PCMs) with high thermal conductivity are essential for thermal energy storage systems, which in turn are indispensible in solar thermal energy applications and efficient use of energy. In this paper, a new palmitic acid (PA)/polyaniline (PANI) form-stable PCMs were prepared by surface polymerization. The highest loading of PA in the form-stable PCMs was 80 mass% with the phase change enthalpy (ΔH _melting) of 175 J g^?1. Copper nanowires (Cu NWs) were introduced to the form-stable PCM by mixing the Cu NWs with PA and ethanol prior to the emulsifying of PA in surfactant solution. The Cu NWs would remain intact in case the ethanol was eliminated before the PA/Cu NWs mixture was mixed with surfactant solution. Otherwise, the Cu NWs would be partially oxidized under the attack of ethanol and ammonium persulfate. The ΔH _melting of the form-stable PCMs containing Cu NWs decreased linearly with the increasing of Cu NWs loading. The ΔH _melting of the form-stable PCMs doped with 11.2 mass% Cu NWs was 149 J g^?1. The thermal conductivity of the form-stable PCMs could be effectively improved by Cu NWs. By adding 11.2 mass% Cu NWs, the thermal conductivity of the form-stable PCM could attain 0.455 W m^?1 K^?1.     

Form-stable electrospun nanofibrous mats as a potential phase change material

A series of Poly vinyl butyral–Poly (acrylic acid) (PVB-PAA) based form-stable phase change materials (PCMs) have been prepared for the use of thermal energy storage applications. Six types of formulations containing five different fatty alcohols were prepared by adding PVB to PAA. Using electrospinning to fabricate nanofibrous mats, our aim was to investigate their properties as form-stable PCMs. Fatty alcohols, 1-Tetradecanol, 1-Hexadecanol, 1-Octadecanol, 1-Eicosanol and 1-Docosanol, were added separately to base formulation. The structural characterization tests were performed by ATR-FTIR spectroscopy. Morphological tests were conducted using Scanning Electron Microscope (SEM). Thermal performances and phase change behaviors were tested by thermogravimetric analysis system (TGA) and differential scanning calorimetry (DSC). The heating cycle phase change enthalpy is measured between 223 and 241?J/g, and the freezing cycle phase change enthalpy is found between 215 and 239?J/g. The main decomposition PVB-PAA based PCMs started at 220?°C. This study suggested that PVB-PAA based PCMs possess well phase change properties and they were found to have an applicable temperature range. With the presented results these materials promise a great potential in thermal energy storage applications.     

换热器与相变材料的兼容性研究进展

相变材料是一类以潜热实现能量存储释放的储能材料,由于其在相变温度附近具有很大的储热密度,相变材料可以被用于建筑控温、太阳能热发电和高温传热蓄热等应用中。 换热器是相变储能设备的重要组成部分,可以将热量在供需两端进行传递和转移,保障需求一方的使用,随着相变材料研究的不断深入及其工程应用的广泛普及,换热器已在众多相变储能项目中发挥了重要的枢纽作用。 为了保证换热器的使用性能,需要对换热器在相变材料中的防腐蚀性进行全面的分析。 本文总结了大量国内外的文献,分析不同成分的相变材料对换热器材料的腐蚀性,为换热器材料的选择提供了参考。