太阳盐/钢渣定型复合相变储热材料的制备与性能研究

全球范围内的能源短缺和环境污染问题迫使人们积极开发可再生新能源。储热技术是解决新能源不稳定性问题的关键技术。相变材料是重要的储热介质之一。熔盐相变材料因其储热密度高,可操作温度范围广的优势,成为储热材料领域研究的热点。为解决熔盐液相易泄漏、低导热和高成本的问题,选择钢渣为基体材料,制备了太阳盐/钢渣定型复合相变储热材料,并通过扫描电子显微镜(SEM),热重–差示扫描量热法(TG–DSC),闪射法导热仪(LFA)和X射线衍射仪(XRD)对复合材料的微观结构、热性能和化学相容性进行了测试与表征。结果表明,钢渣与熔盐质量比5:5的复合材料定型效果最优。复合材料结构紧密;钢渣与熔盐化学相容性良好;复合材料潜热为64.0 kJ/kg,100~500℃内储热密度为945 kJ/kg,热导率高达2.23 W/(m?K)。太阳盐/钢渣复合相变储热材料不仅有利于储热技术的大规模应用,而且为钢铁工业废弃物回收利用提供了良好的参考,对节约资源、保护环境以及提高经济效益具有重要的意义。     

Polymeric phase change composites for thermal energy storage

This article describes a group of thermal energy storage (TES) composites that combine TES and structural functionality. The composites are encapsulations of low melt temperature phase change materials (PCM) such as paraffin waxes in polymer matrices. Room temperature cured bisphenol‐A epoxy and styrene–ethylene–butylene–styrene (SEBS) polymers are chosen as matrix materials because of their excellent chemical and mechanical properties. The polymeric network structure in the composite encapsulates the PCMs, which transform from the solid to the liquid phase. The PCMs provide the energy storage function via the solid–liquid latent heat effect. The resulting composite exhibits dry‐phase transition in the sense that fluid motion of the PCM, when in the liquid phase, is inhibited by the structure of the polymer matrix. The polymer matrix is formulated to provide structural functionality. The latent heat, thermal conductivity and contact conductance, and structural moduli of composites having various PCM‐to‐matrix volume fractions are measured. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1240–1251, 2004     

Polar bear hair inspired ternary composite ceramic aerogel with excellent interfacial bonding and efficient infrared transmittance for thermal insulation

Highly porous, heat resisting ceramic aerogels are considered as promising materials for high-temperature insulation. However, the general structural characteristics of ceramic aerogel, such as poor mechanical strength and transparency to infrared radiation, pose a major obstacle to their practical application. In this paper, we report a general strategy to prepare hollow mullite fiber (HMF) structures by coaxial electrostatic spinning and grow TiO₂ nanorods (TiO₂/NAs) in situ on HMF. The ternary composite ceramic aerogel material was prepared by filling the pores of HMF-TiO₂/NAs with SiCN aerogel. The TiO₂/NAs increased the fiber/aerogel interfacial bonding of the composite (0.392 MPa, 30% strain) and improved the IR transmittance (∼0%, 1200 ℃) without sacrificing their low density and thermal conductivity. In addition, low thermal conductivity (0.041 W/(m·K), 1200 °C) and excellent high-temperature insulation properties allow the composite aerogel to meet the urgent need for lightweight, high-strength, high-temperature insulation systems for spacecraft.     

High thermal conductive shape-stabilized phase change materials based on water-borne polyurethane/boron nitride aerogel

Phase change materials (PCMs) applied in energy storage and temperature control system are important for energy conservation and environmental protection. In this work, structure-adjustable water-borne polyurethane (WPU)/boron nitride (BN) aerogels were synthesized via directional freeze-drying method, and used as supporting scaffolds to confine paraffin wax (PW) and obtain composite phase change materials. The three-dimensional (3D) porous thermal conductivity network of BN was derived by the in-situ ice crystal mound in aerogel, which endows the PW/WPU/BN composite PCM-2.5 with high thermal conductivity (0.96 W m^?1 K^?1) and high energy storage density (140.04 J/g). Shape-stabilized PCMs with high thermal conductivity and excellent electrical insulation prepared by the simple method have great potential for the thermal management of electronic products.     

Form-Stabilized Polyethylene Glycol/Palygorskite Composite Phase Change Material: Thermal Energy Storage Properties,Cycling Stability,and Thermal Durability

In this work, polyethylene glycol (PEG) as a phase change material (PCM) was incorporated with palygorskite (Pal) clay to develop a novel form-stable composite PCM (F-SCPCM). The Pal/PEG(40 wt%) composite was defined as F-SCPCM and characterized using SEM/EDS, FT-IR, XRD, DSC, and TGA techniques. The DSC results revealed that the F-SCPCM has a melting temperature of 32.5°C and latent heat capacity of 64.3 J/g for thermal energy storage (TES) applications. Thermal cycling test showed that the F-SCPCM had good cycling thermal/chemical stability after 500 cycles. The TGA data proved that that both cycled and non-cycled F-SCPCMs had considerable high thermal durability. Consequently, the created F-SCPCM could be considered as an additive material for production of green construction components with TES capability. POLYM. ENG. SCI., 60:909–916, 2020. © 2020 Society of Plastics Engineers     

Preparation and thermal energy storage properties of poly(n‐butyl methacrylate)/fatty acids composites as form‐stable phase change materials

This work is focused on the preparation, characterization, and determination of thermal energy storage properties of poly(n‐butyl methacrylate) (PnBMA)/fatty acid composites as form‐stable phase change material (PCM). In the composite materials, the fatty acids act as latent heat storage material whereas PnBMA serves as supporting material, which prevents the leakage of the melted fatty acids. The maximum encapsulation ratio for all fatty acids was found to be 40 wt%. The composites that do not allow PCM leakage in melted state were identified as form‐stable PCMs. The compatibility of fatty acids with PnBMA is investigated by optical microscopy (OM) and Fourier Transform Infrared (FT‐IR) spectroscopy. Thermal properties and thermal reliability of the form‐stable composite PCMs were determined using differential scanning calorimetry (DSC). DSC analysis revealed that the form‐stable composite PCMs had melting temperatures between 29.62°C and 53.73°C and latent heat values between 67.23 J/g and 87.34 J/g. Thermal stability of the composite PCMs was studied by thermal gravimetric (TG) analysis and the results indicated that the form‐stable PCMs had good thermal stability. In addition, thermal cycling test showed that the composite PCMs had good thermal reliability with respect to the changes in their thermal properties after accelerated 5,000 thermal cycling. On the basis of all results, it was also concluded that the prepared form‐stable composite PCMs had important potential for many thermal energy storage applications such as solar space heating of buildings by using wallboard, plasterboard or floors integrated with PCM. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

基于多孔支撑体的形状稳定复合相变储能材料的研究进展

固-液相变材料（PCMs）是热能储存（TES）技术发展的关键因素,然而一些固有的问题如泄漏和热导率低等严重制约了相变材料的性能。因此,选择合适的方法构建形状稳定的复合相变材料（FSCPCMs）,并有效地提高其热导率是实现相变材料实用化的重要前提。多孔载体封装相变材料为构建具有高储能密度和优异热传输性能的定形复合相变材料提供了一条有效的途径。本文对不同FSCPCMs的制备、结构热学性能、应用等方面进行了综述,详细总结和讨论了孔径和几何形状、表面改性、作用力、组成等因素对FSCPCMs相变行为的影响。重点介绍了具有高热导率、高负载率和高潜热的新型多孔复合相变材料的设计和应用。最后,基于理论、数值和实验方法,展望了FSCPCMs在约束结构中的相变和多尺度传热方面未来的研究方向及其在能源转换方面的商业化应用。     

Preparation and performance study of cordierite/mullite composite ceramics for solar thermal energy storage

The employment of solar energy in recent years has reached a remarkable edge. It has become even more popular as the cost of fossil fuel continues to rise. Energy storage system improves an adjustability and marketability of solar thermal and allowing it to produce electricity in demand. This study attempted to prepare cordierite/mullite composite ceramics used as solar thermal storage material from calcined bauxite, talcum, soda feldspar, potassium feldspar, quartz, and mullite. The thermal physical performances were evaluated and characterized by XRD, SEM, EPMA, and EDS. It was found that the optimum sintering temperature was 1280°C for preparing, and the corresponding water adsorption was 11.25%, apparent porosity was 23.59%, bulk density was 2.10 mg·cm^?3, bending strength was 88.52 MPa. The residual bending strength of specimen sintered at 1280°C after thermal shock of 30 times decreased to be 57 MPa that was 36% lower than that before. The thermal conductivity of samples sintered at 1280°C was tested to be 2.20 W·(m·K)^?1 (26°C), and after wrapped a PCM (phase change materials) of K₂SO₄, the thermal storage density was 933 kJ·kg^?1 with the temperature difference (ΔT) ranged in 0‐800°C. The prepared cordierite/mullite composite ceramic was proved to be a promising material for solar thermal energy storage.     

Preparation of erythritol–graphite foam phase change composite with enhanced thermal conductivity for thermal energy storage applications

Three-dimensional interconnected graphite composite foam as a heat conductive matrix was fabricated by using low cost polymeric precursors and polyurethane (PU) foam as carbon source and sacrificial macroporous template, respectively. Erythritol–graphite foam as a stable composite phase change material (PCM) was obtained by incipient wetness impregnation method. The thermophysical properties such as thermal diffusivity, specific heat, thermal conductivity and latent heat of the erythritol–graphite composite foam were measured. From the results, it was found that the thermal conductivity of the erythritol–graphite composite foam (3.77 W/mK) was enhanced 5 times as compared with that of pristine erythritol (0.72 W/mK). This enhancement can significantly reduce the charging and discharging times of the PCM storage system. There is no chemical reaction between erythritol and graphite as confirmed by X-ray diffractometer (XRD). The PCM/foam composite has a melting point of 118 °C and latent heat of 251 J/g which corresponds to the mass percentage (75 wt.%) of the erythritol within the composite foam. The obtained results confirmed the feasibility of using erythritol–graphite foam as a new phase change composite for thermal energy storage (TES) applications, thus it can contribute to the efficient utilization and recovery of solar heat or industrial waste heat.     

癸酸-石蜡/石墨烯气凝胶定形相变材料的制备及热物性分析

随着碳中和理念的逐步推进,调整能源供应政策,倡导低碳生活,可推动全社会的绿色发展,采用相变材料(PCMs)储存和释放热量,能够有效地利用可再生能源,可减少化石燃料带来的CO₂释放问题。本文利用石墨烯气凝胶作为相变材料的载体,分别采用不同比例的癸酸/石蜡进行有机相耦合,制备了一系列高封装率、低渗漏率的石墨烯定形相变材料。研究发现当石墨烯气凝胶定形相变材料中癸酸/石蜡为7∶3时,相变焓达到202.91J/g。经过200次循环后复合材料的相变潜热变化量在4.25%以内,渗漏率仅为3.20%。采用DSC、TG、XRD、SEM对材料进行微观结构分析说明,石墨烯气凝胶改善了相变介质的形状稳定性,有效地阻止了相变过程中耦合的有机相泄漏,使材料储放热稳定,增强了导热作用,具有良好的应用前景。     

Increment of specific heat capacity of solar salt with SiO2 nanoparticles

Thermal energy storage (TES) is extremely important in concentrated solar power (CSP) plants since it represents the main difference and advantage of CSP plants with respect to other renewable energy sources such as wind, photovoltaic, etc. CSP represents a low-carbon emission renewable source of energy, and TES allows CSP plants to have energy availability and dispatchability using available industrial technologies. Molten salts are used in CSP plants as a TES material because of their high operational temperature and stability of up to 500°C. Their main drawbacks are their relative poor thermal properties and energy storage density. A simple cost-effective way to improve thermal properties of fluids is to dope them with nanoparticles, thus obtaining the so-called salt-based nanofluids. In this work, solar salt used in CSP plants (60% NaNO₃ + 40% KNO₃) was doped with silica nanoparticles at different solid mass concentrations (from 0.5% to 2%). Specific heat was measured by means of differential scanning calorimetry (DSC). A maximum increase of 25.03% was found at an optimal concentration of 1 wt.% of nanoparticles. The size distribution of nanoparticle clusters present in the salt at each concentration was evaluated by means of scanning electron microscopy (SEM) and image processing, as well as by means of dynamic light scattering (DLS). The cluster size and the specific surface available depended on the solid content, and a relationship between the specific heat increment and the available particle surface area was obtained. It was proved that the mechanism involved in the specific heat increment is based on a surface phenomenon. Stability of samples was tested for several thermal cycles and thermogravimetric analysis at high temperature was carried out, the samples being stable.

PACS

65.: Thermal properties of condensed matter; 65.20.-w: Thermal properties of liquids; 65.20.Jk: Studies of thermodynamic properties of specific liquids     

泡沫金属强化石蜡相变蓄热过程可视化实验

相变材料的低热导率是限制潜热蓄热广泛应用的重要原因。将相变材料石蜡真空条件下注入到泡沫金属铜内制备泡沫金属铜-石蜡复合相变材料,通过铜的高热导率及高孔隙材料的大面体比来强化相变换热过程。采用DSC示差扫描量热法对石蜡进行热物性测量获得准确的石蜡相变温度及相变潜热。以管壳式相变蓄热结构为对象,提取对称结构进行可视化设计,对比纯石蜡及泡沫金属铜-石蜡复合材料在相同运行条件下的相变过程,追踪二者熔化过程的相界面位置随时间的演化过程并布置热电偶准确测量材料内部的温度分布。结果显示加入泡沫金属后的复合材料的内部温差明显减小,温度分布均匀,蓄热热通量显著增大,有效缩短相变时间并缓解了自然对流造成的顶部过热和底部不熔化现象。     

Discontinuous carbon fiber/polyamide composites with microencapsulated paraffin for thermal energy storage

This work focuses on the development of multifunctional thermoplastic composites with thermal energy storage capability. A polyamide 12 (PA12) matrix was filled with a phase change material (PCM), constituted by paraffin microcapsules (T_melt = 43 °C), and reinforced with carbon fibers (CFs) of two different lengths (chopped/CF “long”[CFL] and milled/CF “short” [CFS]). DSC tests showed that the melting/crystallization enthalpy values increase with the PCM weight fraction up to 60 J/g. The enthalpy was 41–94% of the expected value and decreased with an increase in the fiber content, because the capsules were damaged by the increasing viscosity and shear stresses during compounding. Long CFs increased the elastic modulus (+316%), tensile strength (+26%), and thermal conductivity (+54%) with respect to neat PA12. Thermal imaging tests evidenced a slower cooling for the samples containing PCM, and once again the CFS-containing samples outperformed those with CFL, due to the higher effective PCM content. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47408.     

Shape-stable phenolic/polyethylene glycol phase change material: kinetics study and improvements in thermal properties of nanocomposites

Storage, transformation, and absorption of energy play effective roles in application and performance of heat and thermal energy beneficiary. Phase change materials (PCMs) are substances with high heat of fusion which can be utilized to design thermal protective and thermal energy storage systems. However, PCM leakage in phase changing process is a well-known disadvantage of the PCM containing systems. One of the approaches to avoid PCM leakage is to prepare shape-stabilized PCM in polymeric composites. In this study, polyethylene glycol (PEG), as a PCM, was shape-stabilized with low leakage in the novolac colloidal structure with no solvent and through a sol–gel in situ polymerization process. Supercooling is a negative associate phenomenon in these systems, which may occur due to the low rate of nucleation and nucleation growth. Nanoclay was used to avoid supercooling of PEG. PEG supercooling significantly decreased when 2.5 wt% of nanoclay was incorporated. This is due to the role of nanoclay particles as the crystal nuclei. The sol–gel polymerization kinetics of novolac resin in the presence of nanoclay and molten PEG was also studied using the Kamal–Sourour model. Results showed that 85 wt% of PEG was preserved with leakage less than 3.5 wt% by shape stabilization encapsulated with colloidal structure of the phenolic resin. Nanoclay improved the thermal properties of the system and reduced the supercooling about 20%. Moreover, based on Kamal–Sourour model, polymerization kinetics could suggest a lower novolac curing rate in the presence of molten PEG and nanoclay.     

Superhydrophobic,heat-resistant alumina-methylsilsesquioxane hybrid aerogels with enhanced thermal insulating performance in high humidity

Heat-resistant alumina aerogels serve as prospective thermal insulating materials in the high-temperature fields, whereas the inherent hydrophilicity and thermal coarsening restrict their thermal insulating application. In this study, superhydrophobic, heat-resistant alumina-methylsilsesquioxane hybrid aerogels (AlMSAs) were prepared via in-situ sol-gel method combined with supercritical drying to overcome the aforesaid obstacles. The transformation from hydrophilicity to hydrophobicity is achieved by regulating the molar ratio of methyltriethoxysilane. The aerogel exhibits homogenous superhydrophobicity with contact angle reaching up to 152.6° when the molar ratio of Al to Si is 2 (AlMSA2). AlMSAs show superior heat resistance up to 1300 °C, suffering no α-Al₂O₃ transition and minor grain growth. Quartz fiber reinforced alumina-based aerogel composite (QFAlMSA2) is prepared to study the thermal insulating performance in practical application. The thermal conductivity of QFAlMSA2 reversibly increases by 5.0% subject to 90% relative humidity (36 °C) for one month due to the superhydrophobicity. QFAlMSA2 exhibits a low thermal conductivity of 0.0542 W/(m·K) after being calcined at 1200 °C and a moderate temperature of 113 °C when exposed to a butane flame for 30 min. This study offers meaningful insights into developing alumina-based aerogel materials for high-moisture and high-temperature thermal insulations.     

泡沫铜/石蜡复合相变储能材料的储放热过程及数值模拟

作为储热和热管理技术的重要材料之一,相变储能材料通常具有储热密度较大、相变温度变化较小的优势,但其热导率较低,热传递效率较差。本文将泡沫铜用于石蜡相变储能材料的传热强化,通过测定相变储能材料储放热过程的温度变化,考察了添加泡沫铜对相变储能材料储放热速率和温度均匀性的影响,且在实验基础上对储能材料的放热过程进行建模并求解,得到温度云图,为实际应用提供理论依据。结果表明,添加泡沫铜后,石蜡的相变储热和放热时间分别缩短了16.67%和14.71%;储放热过程复合材料中心层与外层中心点的最大温差分别降低了91.5%和87.5%;建立放热过程相变储能材料温度随时间变化的模型,对比实际值和模型预测值,得到相关系数及标准误差分别为0.99℃和0.13℃,证明该模型准确度较高,可有效预测相变储能材料的温度变化情况。     

壳管式潜热蓄能系统换热特性

针对目前石蜡潜热蓄能系统效率低下的特点,构建了石蜡/膨胀石墨混合相变材料的潜热蓄能系统,研究了其蓄/放热特性,并与纯石蜡相变材料系统进行了对比分析,讨论了不同换热流体流量下的蓄/放热过程的时间周期。用焓法处理相变区域,对该潜热蓄能系统的整体蓄热过程进行数值模拟。研究结果表明,对于石蜡／膨胀石墨复合相变材料,其导热性能较纯石蜡有很大提高,但由于添加了膨胀石墨而减弱了蓄热中石蜡的对流换热。流量提高对蓄/放热速率有明显的改善。焓法模型能全面反映蓄能系统的换热与流动特性,数值计算的结果与实验数据吻合较好。     

Low molecular weight paraffin,as phase change material,in physical and micro-structural changes of novel LLDPE/LDPE/paraffin composite pellets and films

Latent heat storage system by phase change materials is an effective method to achieve high density energy storage. A novel composite pellet consisted of a blend of linear low density polyethylene and low density polyethylene (LLDPE/LDPE) with low molecular weight paraffin (a phase change material, at 25 and 50 wt%) has been developed and coated by calcium silicate to prevent paraffin leakage. Three-layer coextruded films containing the paraffin composites as the middle layer have been prepared from each group for application as plastic film cover to control undesirable temperature variations during the storage of agricultural crops. The Melt Flow Index and thermal properties of the pellets as well as the quantity of paraffin leakage were studied. Thermal/morphological and permeation properties of the coextruded films have been investigated. The results showed that the LLDPE/LDPE polymer matrix provided an appropriate structural morphology for low molecular weight paraffin (n < 18) entrapment with good miscibility and low paraffin leakage (< 5%). Based on differential scanning calorimetry (DSC) thermographs, this type of paraffin may promote the compatibility between linear and low-density polyethylene. A dispersion-type morphology was observed in the micrograph of LLDPE/LDPE film, where the sizes of the spherical micro-domains were reduced as evident in the microscopic images of the paraffin-containing composite films. At storage temperatures below the phase change temperature (T < 25 °C), the oxygen permeability was substantially decreased because of the combined effects of paraffin crystallites and calcium silicate.     

Expanded Vermiculite/Paraffin Composite as a Solar Thermal Energy Storage Material

A solar thermal energy storage material was prepared from expanded vermiculite (EVM) and paraffin by vacuum impregnation. Samples were characterized by thermogravimetric and differential scanning calorimetry (TG‐DSC), X‐ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), scanning electron microscopy (SEM), petrographic analysis, and thermal conductivity measurements. The results indicated that EVM existed as a phlogopite structure in the EVM/paraffin composite. The composite latent heat was 137.6 J/g at the freezing temperature of 52.5°C and 135.5 J/g at the melting temperature of 48.0°C, when the paraffin content was 67%. The phlogopite structure of EVM benefited paraffin heat transfer because the composite exhibited a thermal conductivity of 0.545 W·(m·K)^?1 higher than that of paraffin. Morphology and structural changes of EVM during composite preparation were investigated. The composite exhibited excellent thermal stability and has potential application in solar thermal energy storage and solar heating.     

Corrosion behavior of metallic alloys in molten chloride salts for thermal energy storage in concentrated solar power plants: A review

Recently, more and more attention is paid on applications of molten chlorides in concentrated solar power (CSP) plants as high-temperature thermal energy storage (TES) and heat transfer fluid (HTF) materials due to their high thermal stability limits and low prices, compared to the commercial TES/HTF materials in CSP-nitrate salt mixtures. A higher TES/HTF operating temperature leads to higher efficiency of thermal to electrical energy conversion of the power block in CSP, however causes additional challenges, particularly increased corrosiveness of metallic alloys used as containers and structural materials. Thus, it is essential to study corrosion behaviors and mechanisms of metallic alloys in molten chlorides at operating temperatures (500–800 °C) for realizing the commercial application of molten chlorides in CSP. The results of studies on hot corrosion of metallic alloys in molten chlorides are reviewed to understand their corrosion behaviors and mechanisms under various conditions (e.g., temperature, atmosphere). Emphasis has also been given on salt purification to reduce corrosive impurities in molten chlorides and development of electrochemical techniques to in-situ monitor corrosive impurities in molten chlorides, in order to efficiently control corrosion rates of metallic alloys in molten chlorides to meet the requirements of industrial applications.