Recent progress in thermal energy storage materials

本文结合储热材料的分类、特点、应用及存在的问题对储热材料的最新研究进展进行了综述,主要包括有机相变储热材料、熔融盐类相变储热材料、合金相变储热材料及复合类储热材料。探讨了储热材料成分组成、制备工艺及性能特点,进一步介绍了其最新研究进展,并对储热材料的下一步研究进行了展望,提出开发高性能纳微复合结构储热材料是未来研究的重点。     

Recent progress and prospective of medium and high temperatures thermal energy storage materials

开发中高温储热材料及其制备方法是储热技术发展的关键之一.本文结合中高温储热材料的分类,特点,应用及存在的问题对中高温储热材料的研究进展进行了综述,主要包括显热储热材料,热化学储热材料以及潜热储热材料.探讨了复合结构储热材料及其制备工艺,进一步介绍了其最新研究进展,并对中高温储热材料的下一步研究进行了展望,提出开发高性能纳微复合结构储热材料是未来研究的重点.     

储热材料的研究进展及其应用

综述了储热材料的研究进展和实际应用.介绍了储热材料的分类以及各类材料的性能、储能机理和优缺点;介绍了一些新型的相变材料,并结合实例探讨了储热材料在太阳能利用、建筑节能等领域的应用;指出了储热材料的研究方向和未来的发展趋势.     

Design of three-dimensional interconnected porous hydroxyapatite ceramic-based composite phase change materials for thermal energy storage

In this article, three-dimensional connected porous hydroxyapatite ceramics (PHCs) were prepared by using the Pickering emulsion template, which possessing controlled pore structure simply by adjusting the solid content from 35 to 55 wt%. The polyethylene glycol (PEG) and PHCs were compounded by vacuum impregnation to acquire composite phase change materials (CPCMs) with admirable shape stability. The SEM and EDS images showed that PEG was successfully adsorbed in the pore, and the results of FT-IR, XRD, TGA, and thermal cycles test, demonstrated the CPCMs possessed satisfactory chemical stability, favorable thermal stability, and wonderful thermal reliability. The maximum package ratio obtained was 66 wt%, which was supported by the PHC sample prepared with a solid content of 40 wt%. Moreover, the phase transition temperature and latent heat during melting and solidification were 53.41°C and 117.5 J/g, 36.49°C and 111.1 J/g, respectively. Therefore, the prepared PCM composites had a controlled pore structure, stable chemical properties, high latent heat, and excellent thermal reliability, making it a reliable application of thermal energy storage.     

Encapsulated phase change materials for thermal energy storage: Experiments and simulation

In the present study, encapsulated phase change materials (PCMs) were used for the storage of thermal energy. Both experiments and simulation were performed to evaluate the characteristics of encapsulated PCMs. Tests were conducted in a packed bed to determine the performance of the encapsulated PCM. In the preparation of encapsulated PCMs, the coacervation technique was used. The performance of the encapsulated PCM was evaluated in terms of encapsulation ratio, hydrophilicity, and energy storage capacity. The experiments were designed, based on surface response method, to optimize the processing conditions. It was found that a higher coating to paraffin ratio led to a higher paraffin encapsulation ratio. The hydrophilicity value of encapsulated paraffin depended mainly on the ratio of paraffin to coating. The higher the ratio, the lower was its product hydrophilicity. When the paraffin to coating ratio was constant, the higher concentration of HCHO led to a lower hydrophilicity of the product. The encapsulated paraffin has shown large energy storage and release capacity (20–90 J g^?1) during its phase changes depending on different ratios of paraffin to coating. Thermal cyclic test showed that encapsulated paraffin kept its geometrical profile and energy storage capacity even after 1000 cycles of operation. In the experiments and simulation of fluid heating process in encapsulated PCM charged packed bed, results showed that Eulerian granular multiphase model in FLUENT 4.47 is suitable for simulation of such a system. Copyright © 2002 John Wiley & Sons, Ltd.     

Heat transfer behaviour of thermal energy storage components using composite phase change materials

对基于复合相变材料储热单元的储热性能进行了研究。建立了复合材料和储热单元体内部的二维传热模型,考察了复合材料物性和结构尺寸及传热流体操作条件（流体流速）对单元体储热性能的影响,对比了两种不同结构单元体的储热性能,并搭建实验平台进行了实验对比研究。对比结果表明,模型结果与实验结果趋于一致,验证了模型的准确性。复合材料物性和结构尺寸及传热流体操作条件对单元体储热性能有较大的影响。相比较单管储热单元体,同心管储热单元体有着更优的储热特性,在相同的操作条件下,同心管储热单元体的储热、放热时间较单管储热单元体分别减少10%和15%。     

Microencapsulation of a eutectic PCM using in situ polymerization technique for thermal energy storage

In the present work, microencapsulated phase change material (M-PCM) has been synthesized with eutectic mixture (75% SA + 25% CA) as core and melamine formaldehyde (MF) as shell using in situ polymerization. Advanced instrumental techniques like field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), particle size analyzer (PSA), thermogravimetric/differential thermal analysis (TG/DTA), differential scanning calorimetry (DSC), and thermal conductivity analyzer (TCi) were used to characterize the synthesized M-PCM, and impact of effective parameters like pH and agitator speed on the encapsulation process was also elucidated. Results obtained reveal that at the optimized pH (3.2) and agitator speed (1500 rpm) M-PCM possess smooth surface morphology, spherical in shape with particle size of 10.41 μm. Based on FT-IR analysis, it was observed that the synthesized M-PCM was uniformly encapsulated by MF resin with eutectic mixture in the core. The encapsulation process results in the improvement of the thermal stability of eutectic mixture, it increases from 202.5 to 212.3°C, and the encapsulation efficiency of the M-PCM is found to be 85.3%. The melting point and latent heat of fusion of M-PCM were found to be 34.5°C and 103.9 kJ/kg, respectively.     

相变储能建筑材料的研究进展

相变储能建筑材料是相变材料与建材基体复合制备的一种新型储能建筑材料。本文分析了相变材料的筛选和改进方法及其封装技术的研究现状,介绍了相变材料与建材基体复合工艺,系统阐述了相变储能建筑材料的作用机理和应用现状,并指出了相变储能建筑材料在实际应用中存在的一些问题,最后展望了相变储能建筑材料的发展前景。     

节能的地下含水层蓄热(冷)器

分析了地下含水层蓄热（冷）的特点，阐述了使用含水层蓄热（冷）的系统节能和环保的重要意义，介绍了一些欧洲应用实例。     

Review on solar thermal energy storage technologies and their geometrical configurations

Because of the unstable and intermittent nature of solar energy availability, a thermal energy storage system is required to integrate with the collectors to store thermal energy and retrieve it whenever it is required. Thermal energy storage not only eliminates the discrepancy between energy supply and demand but also increases the performance and reliability of energy systems and plays a crucial role in energy conservation. Under this paper, different thermal energy storage methods, heat transfer enhancement techniques, storage materials, heat transfer fluids, and geometrical configurations are discussed. A comparative assessment of various thermal energy storage methods is also presented. Sensible heat storage involves storing thermal energy within the storage medium by increasing temperature without undergoing any phase transformation, whereas latent heat storage involves storing thermal energy within the material during the transition phase. Combined thermal energy storage is the novel approach to store thermal energy by combining both sensible and latent storage. Based on the literature review, it was found that most of the researchers carried out their work on sensible and latent storage systems with the different storage media and heat transfer fluids. Limited work on a combined sensible-latent heat thermal energy storage system with different storage materials and heat transfer fluids was carried out so far. Further, combined sensible and latent heat storage systems are reported to have a promising approach, as it reduces the cost and increases the energy storage with a stabilized outflow of temperature from the system. The studies discussed and presented in this paper may be helpful to carry out further research in this area.     

Verification of hydrothermal stability of adsorbent materials for thermal energy storage

This paper presents an experimental protocol for the cycling stability of adsorbent materials for thermal energy storage (TES) applications under hydrothermal conditions. Two different aging conditions were identified, namely, cycle and shelf test. The former one mimicking the cycling between desorption and adsorption conditions, while the latter one keeping a constant temperature for long time under constant water vapor pressure. A flexible experimental setup was then designed and realized to contemporarily perform both aging condition under selectable operating conditions. The protocol defines different characterization methods to compare the fresh and the aged samples. The measurement of the water vapor adsorption equilibrium isobars represents the main parameter to directly highlight possible degradation phenomena. Subsequently, X‐ray diffraction patterns (XRD), nitrogen physisorption, and scanning electron microscopy coupled to energy dispersive x‐ray (SEM–EDX), are used to evaluate structural, textural, morphological, and elemental composition variation that can help in identifying the causes of possible degradation. The proposed protocol was employed to validate the stability of a commercial adsorbent, AQSOA Z02, that proved a quite stable behavior both under cycle and shelf investigated conditions.     

Review on storage materials and thermal performance enhancement techniques for high temperature phase change thermal storage systems

Designing a cost-effective phase change thermal storage system involves two challenging aspects: one is to select a suitable storage material and the other is to increase the heat transfer between the storage material and the heat transfer fluid as the performance of the system is limited by the poor thermal conductivity of the latent heat storage material. When used for storing energy in concentrated solar thermal power plants, the solar field operation temperature will determine the PCM melting temperature selection. This paper reviews concentrated solar thermal power plants that are currently operating and under construction. It also reviews phase change materials with melting temperatures above 300 °C, which potentially can be used as energy storage media in these plants. In addition, various techniques employed to enhance the thermal performance of high temperature phase change thermal storage systems have been reviewed and discussed. This review aims to provide the necessary information for further research in the development of cost-effective high temperature phase change thermal storage systems.     

Using demolition wastes from urban regeneration as sensible thermal energy storage material

Efficient use of solar energy in industrial applications calls for a cost‐effective thermal energy storage (TES) system. Packed bed is a viable technology for high‐temperature TES applications. The packing material acting as the TES material has to be sustainable with favorable thermal properties and compatible with the heat transfer fluid. Demolition wastes—leftovers from urban regeneration projects—in many countries are a big burden economically and environmentally. This paper aims to investigate the potential of using demolition wastes as sensible thermal energy storage (STES) material in packed bed column for industrial solar applications below 300°C. STES material samples have been prepared using binding additives with demolition waste dust. Chemical composition, mechanical strength, and thermal analysis tests have been carried out to determine suitability of STES samples. The DSC results showed that new STES samples had average specific heat capacity of 1000 to 1460 J/kg C in temperature range of 100°C to 500°C. The samples were thermally stable until 750°C under TGA analysis. These results showed that demolition wastes are potential low‐cost sensible heat storage material for applications up to 750°C. Furthermore, valorization of demolition wastes as sensible heat storage material is a sustainable approach in reducing fossil fuel consumption of high‐temperature industrial applications and avoiding the use of natural resources as packing material.     

Experimental research on thermal characteristics of PCM thermal energy storage units

To explore thermal management integration in electric vehicles (EVs), a phase change materials (PCMs) thermal energy storage unit using flat tubes and corrugated fins is designed. The investigation focuses on the thermal characteristics of the PCM unit, such as the temperature variation, heat capacity, and heat transfer time, etc. Meanwhile, the heat storage and release process will be influenced by different inlet temperature, liquid flow rate, melting point of the PCM, and the combination order of the units. Under the same inlet temperature and flow rate condition, the PCM unit with higher melting point enters the latent heat storage stage slowly and enters the phase change melting release stage quickly. Furthermore, the heat storage and release rates increase with increasing liquid flow rates, but the effects are diminishing in the middle and later periods. The multiple PCM units with different melting temperatures are cascaded to help recycle low-grade heat energy with different temperature classes and exhibit well heat storage and release rates.     

Development and characterization of form-stable porous TiO2/tetradecanoic acid based composite PCM with long-term stability as solar thermal energy storage material

The present study focused on the preparation of form-stable composites of 1-tetradecanoic acid (TDA)/titanium dioxide (TiO₂) powder via a facile impregnation method. The use of powdered TiO₂ as porous material and thermal conductivity enhancer for TDA is a novel attempt. The morphological, chemical, and crystalline properties of form-stable composite PCMs (Fs-CPCMs), containing different amounts of TiO₂, were characterized using field emission scanning electron microscope, Fourier transform infrared spectroscopy, and X-ray diffraction techniques. The finding supports that the produced composites were chemically and structurally stable. The latent heat storage (LHS) properties of composites were obtained from differential scanning calorimeter instrument, and the findings revealed that the Fs-CPCM with 50 mass% TDA has a melting temperature of 52.04°C and a considerably good LHS capacity of 97.75 J/g. The thermal conductivity of TDA was increased remarkably by the addition of TiO₂ micro particles. The results obtained from thermogravimetric analysis and thermal cycling test exhibited that the Fs-CPCM, containing 50 mass% TiO₂, possesses great thermal degradation durability, cycling chemical stability, and thermal reliability. This composite PCM can be very well used for passive thermal management of electronic devices, automotive components, photovoltaic thermal hybrid designs, solar air/water heating systems, etc.     

Melting of PCM in a thermal energy storage unit: Numerical investigation and effect of nanoparticle enhancement

The present paper describes the analysis of the melting process in a single vertical shell‐and‐tube latent heat thermal energy storage (LHTES), unit and it is directed at understanding the thermal performance of the system. The study is realized using a computational fluid‐dynamic (CFD) model that takes into account of the phase‐change phenomenon by means of the enthalpy method. Fluid flow is fully resolved in the liquid phase‐change material (PCM) in order to elucidate the role of natural convection. The unsteady evolution of the melting front and the velocity and temperature fields is detailed. Temperature profiles are analyzed and compared with experimental data available in the literature. Other relevant quantities are also monitored, including energy stored and heat flux exchanged between PCM and HTF. The results demonstrate that natural convection within PCM and inlet HTF temperature significantly affects the phase‐change process. Thermal enhancement through the dispersion of highly conductive nanoparticles in the base PCM is considered in the second part of the paper. Thermal behavior of the LHTES unit charged with nano‐enhanced PCM is numerically analyzed and compared with the original system configuration. Due to increase of thermal conductivity, augmented thermal performance is observed: melting time is reduced of 15% when nano‐enhanced PCM with particle volume fraction of 4% is adopted. Similar improvements of the heat transfer rate are also detected. Copyright © 2012 John Wiley & Sons, Ltd.     

Emulsification of thermal energy storage materials in an immiscible fluid

The problems of thermal energy storage are of major importance in the development of intermittent energy sources and the efficient usage of conventional energy supplies. Utilization of latent heat materials for thermal energy storage has been plagued by the build-up of solids on cooling surfaces and the resulting low heat transfer rates. A novel system has been investigated in order to alleviate these difficulties. Small droplets of latent heat material were suspended in an immiscible heat transfer fluid to form an emulsion. The generation of stable emulsions is an empirical art, for which the selection of surface-active agents and the method of mixing play the key roles. A total of 42 latent heat storage emulsion samples were prepared using a diphenyl compound as the organic phase. Most of the samples were prepared using a high speed mixing apparatus. Several emulsified blends exhibited favourable prolonged storage and cycling behaviour. Estimates based on apparent viscosity measurements indicated that high rates of heat transfer could be obtained with this system. Assuming turbulent flow conditions and 60 per cent salt loading, a value for the mean film coefficient of heat transfer was calculated to be about 1045 J/m² s °C. The concept offers potentially large heat exchanger cost reductions, while retaining 60 per cent of the volume savings attainable in latent heat systems.     

Corrosion of metal containers for use in PCM energy storage

In recent years, thermal energy storage (TES) systems using phase change materials (PCM) have been widely studied and developed to be applied as solar energy storage units for residential heating and cooling. These systems performance is based on the latent heat due to PCM phase change, a high energy density that can be stored or released depending on the needs. PCM are normally encapsulated in containers, hence the compatibility of the container material with the PCM has to be considered in order to design a resistant container. Therefore, the main aim of this paper is to study the corrosion effects when putting in contact five selected metals (aluminium, copper, carbon steel, stainless steel 304 and stainless steel 316) with four different PCM (one inorganic mixture, one ester and two fatty acid eutectics) to be used in comfort building applications. Results showed corrosion on aluminium specimens. Hence caution must be taken when selecting it as an inorganic salt container. Despite copper has a corrosion rate range of 6–10 mg/cm² yr in the two fatty acid formulations tested, it could be used as container. Stainless steel 316 and stainless steel 304 showed great corrosion resistance (0–1 mg/cm² yr) and its use would totally be recommended with any of the studied PCM.     

Form-stable phase change materials for thermal energy storage

The present paper considers the state of investigations and developments in form-stable phase change materials for thermal energy storage. Paraffins, fatty acids and their blends, polyethylene glycol are widely used as latent heat storage component in developing form-stable materials while high-density polyethylene (HDPE), styrene-butadiene-styrene (SBS) triblock copolymer, Eudragit S, Eudragit E, poly (vynil chloride) (PVC), poly (vynil alcohol) (PVA) and polyurethane block copolymer serve as structure supporting component. A set of organic and metallo-organic materials with high transition heat in solid-solid state is considered as perspective for-stable materials to store thermal energy. Another perspective class of form-stable materials are the materials on the basis of such porous materials as expanded perlite and vermiculite impregnated with phase change heat storage materials. The technology of producing new form-stable ultrafine heat storage fibers is developed. It opens availability to produce the clothers with improved heat storage ability for extremely cold regions. The perspective fields of application of form-stable materials are discussed. The further directions of investigations and developments are considered.     

节能建筑用蓄热材料的释热性能实验研究

相变材料在发生相变的过程中吸收或者释放热量，在太阳能利用、建筑节能和空调采暖方面有着广阔的应用前景。通过实验研究了可用于节能建筑的相变材料——硫酸钠水合盐体系相变材料的释热性能，研究了不同增稠剂和成核剂对其放热性能的影响，对节能建筑用相变建材的研究有参考价值。