组合相变材料储热系统的储热速率研究

建立了组合式柱内封装相变材料熔化－固化循环相变储热系统的物理模型,用有限差分法进行了数值模拟求解。结果表明,与采用单一相变材料的传统储热系统相比,在给定相变材料组合方式和传热流体进口温度条件下,传热流体流量存在最佳值;选用三种石蜡作用相变材料和水作传热流体的模拟计算结果表明,相变速率可提高１５％￣２５％左右。     

太阳能热发电储热材料研究进展

综述了太阳能热发电储热材料研究进展.分别介绍了浇注料、混凝土储热材料、液态显热储热、硝酸盐叠层相变储热、金属相变储热和氨热化学反应储热材料,分析了它们各自的优缺点,并展望了太阳能热发电储热材料的发展前景.     

高温复合相变材料储热电暖器的储热性能CSCD

本文研究了基于高温复合相变材料的相变储热电暖器,对其储热性能、内部流场和温度分布及温度调控机制进行了实验和模拟研究,并与镁砖显热电暖器的储热性能进行对比。结果表明这类相变储热电暖器的储热平均温度高、平均温差小、出风口温度高,整体性能要优于镁砖显热电暖器。相同体积下两种电暖器储热量相当,但相变储热电暖器的重量可减轻1.6倍;在相同储热时间和储热温度下,同等重量的相变储热电暖器较镁砖电暖器可多储热68%。结果也展示了这类储热电暖器温度控制测点选择的重要性,当选取距离加热单元10 mm处的测点作为温度调控点时,电暖器内的平均温度和储热砖体的最高温度均能满足安全要求,而且加热单元电源在谷电8 h储热过程中只需启停两次。     

含碳二元系相变储热材料储热性能分析选择北大核心CSCD

相变储热技术与聚光太阳能发电技术相结合可以提高太阳能的利用率,减缓化石燃料燃烧带来的环境压力。本文通过分析相变储热材料的选择标准,对筛选出具有研究价值的含碳二元系相变储热材料的性能特别是热物理性能进行分析。研究发现,硅、硼、铝、铬、铁单质材料与碳元素形成的二元化合物或固溶体具有较高的熔点,形成的含碳二元系相变储热材料在高温相变储热领域应用前景广阔。在含碳二元系相变储热材料中,Fe-C二元合金可满足高温相变储热系统1100~1500℃的相变储热要求,当合金为含碳4.3%的Fe-C共晶成分时,Fe-C二元合金的相变潜热理论值为611 kJ/kg,热导率约为(40±16)W/(m·K),相变温度为1148℃,具有相对其他合金成分更为优异的综合储热性能可用于聚光太阳能热发电系统储热。     

列管式相变储热单元的优化模拟CSCD

列管式换热器具有结构牢固、传热面积大、材料使用适应性强等优点,是相变储热领域应用较为广泛的一种换热器。但由于大部分相变材料热导率偏低,导致换热器的换热性能较差,因此提高相变储热器的储热效率,是目前国内外研究的热点。本工作对列管式相变储热单元进行了二维非稳态模拟优化,研究了换热器结构、翅片数目及中心距3种参数对储热性能的影响,并探讨了熔化过程中相变材料的温度和液相率变化趋势。研究结果表明,与圆形换热器结构相比,正方形换热器储热性能更优;相比于无翅片的储热换热器,添加翅片后储热性能得到显著提升,相变材料熔化时间缩短66％;对中心距而言,在一定范围内,随中心距减小进出口降压增大,但储热性能相应提高。     

相变储热研究进展(2)组合相变材料储热与应用潜力

本文从两个方面总结了相变储热（ＬＴＥＳ）的研究现状：①ＬＴＥＳ在太空太阳能动力（ＤＢＰ）发电系统和建筑物围护结构中的应用;②组合相变材料储热系统的研究历程和最新进展。     

储热技术研究进展与展望

储热技术在解决可再生能源间歇性问题和提高能源利用效率等方面发挥着重要作用。本文针对储热技术的研究进展,分别从材料、装置、系统、政策干预等方面进行了综述。针对储热材料的性能提升,本文对构建复合型储热材料的配方研究、材料特性的微观模拟研究,及其相关的制备技术进行了总结。此外,随着高温熔融盐储热材料在光热发电系统中的广泛应用,本文对其产生的高温腐蚀行为与腐蚀防护技术进行了概述。储热装置方面,本文重点介绍了板式、填充床式和管壳式储热单元的强化传热方法。储热系统与应用方面,本文对基于相变储热和热管理、热化学储热、液态空气储能的应用研究进行了概述。最后,储热技术的发展离不开适当的政策干预,因此本文对不同国家针对储热技术制定的相关政策进行了报道。     

组合相变材料储热的实验研究

分析了在同一储热系统中采用两种或两种以上相变材料的特点,介绍了用于组合相变材料储热研究的实验装置,给出了四种相变材料水平柱状储热单元储热系统的初步测试结果,并对其进行了讨论。     

螺旋盘管式相变储热单元储热性能

以石蜡作为相变材料,制作了内通流体螺旋盘管结构的相变储热单元。在对储热单元储热过程进行传热分析的基础上,利用实验手段对储热单元在不同工况下的储热性能进行了研究。通过对其储热过程中相变材料相变过程的分析,提出储热器设计的优化方案。利用实验数据得到其准则关联式,为其在工程中的应用提供了依据。     

套管式相变储热单元储热换热性能的研究

基于石蜡相变材料,对同心套管式相变储热单元的融化过程进行了二维非稳态数值研究。在考虑自然对流的前提下,对比了内传热管和外传热管储热单元的换热特性,得到了相变材料的温度场分布、流线图和相变界面位置随时间的变化规律,并研究了史蒂芬数、瑞利数对储热换热性能的影响。结果表明,在融化相同体积相变材料前提下,外传热管储热单元可以缩短60.7%的融化时间,换热特性明显优于内传热管式储热单元,这对与变储热装置的优化设计提供参考依据。     

Experimental study on charging processes of a cylindrical heat storage capsule employing multiple‐phase‐change materials

This paper mainly deals with the charging processes of a cylindrical heat storage capsule filled with stearic acid, sliced paraffin and lauric acid as phase‐change materials (PCMs). Experimental results demonstrate that, compared to the capsule with a single PCM, the charging rate of the capsule employing three PCMs is enhanced obviously. Copyright © 2001 John Wiley & Sons, Ltd.     

相变蓄热供热装置热性能试验研究与系统经济性分析

为分析相变蓄热装置在充热和放热过程中的热性能,设计并搭建一套相变蓄热供热装置中试实验系统,研究主要运行参数对相变蓄热装置热性能的影响;在此基础上,结合项目案例,对相变蓄热供热系统经济性进行分析。结果表明：相变材料(Phase Change Material, PCM)凝固过程中的传热主要受相变介质内部导热控制;而在其熔化过程中自然对流对传热起重要控制作用;蓄热装置充热速率快于放热速率。提高传热流体流量有助于增强PCM中的热传递,缩短充/放热时间,但蓄热装置内PCM温度分布均匀性有所降低;为降低系统能耗,提高储放热效率,优先选用小流量进行充/放热。该相变蓄热供热项目的动态投资回收期为3.55年,具有良好的经济性。研究结果可对相变蓄热供热系统的设计及应用推广提供参考依据。     

Experimental study of the phase change and energy characteristics inside a cylindrical latent heat energy storage system: Part 2 simultaneous charging and discharging

The time mismatch between energy availability and energy demand with solar domestic hot water (SDHW) systems is often solved using energy storage. Energy storage systems typically employ water for thermal energy storage, however, water storage takes up considerable space and weight due to the large volumes required under certain conditions. A latent heat energy storage system (LHESS) may provide a valuable solution to the space and weight issue, while also correcting the energy mismatch by storing energy in phase change materials (PCMs) when it is available, dispensing energy when it is in demand, and acting as a heat exchanger when there is supply and demand simultaneously. PCMs are advantageous as energy storage materials due to their high energy density which reduces the space requirements for energy storage. However, heat transfer problems arise due to the inherently low thermal conductivity of PCMs. Simultaneous charging and discharging has not been addressed in literature making questionable the ability of a LHESS to operate as a heat exchanger during the mode of operation. The main objective of this research is to study the heat transfer processes and phase change behavior of a PCM during simultaneous charging and discharging of a LHESS.In Part 2 of this paper, experiments are performed using a vertical cylindrical LHESS which is charged and discharged simultaneously to replicate latent heat energy storage paired with a SDHW system with simultaneous energy supply and demand. Dodecanoic acid is used as the PCM. Experimental results for simultaneous operations are presented, under various scenarios and flow rates for both the hot and cold heat transfer fluids. The ability of the system to directly transfer heat between the hot and cold heat transfer fluids is studied, and the results found during consecutive, or separate, charging and discharging, presented in Part 1 of this paper, are compared to the results found during simultaneous charging and discharging. It was found that natural convection in the melted PCM clearly provides an advantage towards direct heat exchange between the hot and cold heat transfer fluid; while the low thermal conductivity of solid PCM provides a barrier to this direct energy exchange.     

球形单元储热装置蓄热特性的分析与优化

为提高太阳能利用率，设计一套相变蓄热装置，研究球形相变单元蓄热影响因素，保持相变材料（PCM）总质量维持在较小浮动范围内，对比不同直径、孔隙率、层间距，探究整个装置的蓄热性能。实验与模拟结果表明：同等条件下，相变球直径越小，蓄热时间越短。而考虑到加工制造难度及成本，直径为46或50 mm的蓄热球是最优选择；孔隙率、入口温度和入口流量对整体蓄热时间影响较大；相反，改变蓄热球层间距对蓄热时间的影响较小。     

Review of thermal energy storage for air conditioning systems

Thermal energy storage is very important to eradicate the discrepancy between energy supply and energy demand and to improve the energy efficiency of solar energy systems. Latent heat thermal energy storage (LHTES) is more useful than sensible energy storage due to the high storage capacity per unit volume/mass at nearly constant temperatures. This review presents the previous works on thermal energy storage used for air conditioning systems and the application of phase change materials (PCMs) in different parts of the air conditioning networks, air distribution network, chilled water network, microencapsulated slurries, thermal power and heat rejection of the absorption cooling. Recently, researchers studied the heat transfer enhancement of the thermal energy storage with PCMs because most phase change materials have low thermal conductivity, which causes a long time for charging and discharging process. It is expected that the design of latent heat thermal energy storage will reduce the cost and the volume of air conditioning systems and networks.     

The value of thermal radiation in assessing the charge/discharge rate of high‐grade thermal energy storage using encapsulated phase change materials (PCMs)

The charge/discharge rate of a spherical phase change material (PCM) capsule was assessed in consideration of phase change phenomenon and the combined effect of thermal radiation and heat convection in the charging/discharging processes. The heat transfer model was developed based on a single PCM capsule. The equivalent heat flux was evaluated by using the thermal resistance method. In consideration of the thermal radiation, the equivalent charge/discharge rate was improved, and the temperature rising of the PCM was actually much faster in the charging/discharging processes. It was indicated that the influence of the thermal radiation became more significant for PCM capsules under a small Re number (constant air velocity) and for high‐grade thermal energy storage. The analytical results showed that the highest heat flux contributed by cold thermal radiation occupied 30% and 62% of that by heat convection for PCM capsules with radius of 10 and 40 mm, respectively. This illustrated the crucial value of thermal radiation on the charge/discharge rate of PCM capsules with a large radius. However, for smaller size PCM capsules, the equivalent heat flux was larger under the same fluid flow velocity, and it decreased more promptly with time, because the heat convection that played the dominant role in charge/discharge processes was sensitively affected by the radius of the PCM capsules. Copyright © 2016 John Wiley & Sons, Ltd.     

A review on thermal energy storage systems in solar air heaters

The drying needs of agricultural, industrial process heat requirements and for space heating, solar energy is one of the prime sources which is renewable and pollution free. As the solar energy is inconsistent and nature dependent, more often there is a mismatch between the solar thermal energy availability and requirement. This drawback could be addressed to an extent with the help of thermal energy storage systems combined with solar air heaters. This review article focuses on solar air heaters with integrated and separate thermal energy storage systems as well as greenhouses with thermal storage units. A comprehensive study was carried out in solar thermal storage units consisting of sensible heat storage materials and latent heat storage materials. As the phase change heat storage materials offer many advantages over the sensible heat storage materials, the researchers are more interested in this system. The charging and discharging characteristics of thermal storage materials with various operational parameters have been reported. All the possible solar air heater applications with storage units have also been discussed.     

Numerical analysis of latent heat thermal energy storage using encapsulated phase change material for solar thermal power plant

Thermal energy storage improves the load stability and efficiency of solar thermal power plants by reducing fluctuations and intermittency inherent to solar radiation. This paper presents a numerical study on the transient response of packed bed latent heat thermal energy storage system in removing fluctuations in the heat transfer fluid (HTF) temperature during the charging and discharging period. The packed bed consisting of spherical shaped encapsulated phase change materials (PCMs) is integrated in an organic Rankine cycle-based solar thermal power plant for electricity generation. A comprehensive numerical model is developed using flow equations for HTF and two-temperature non-equilibrium energy equation for heat transfer, coupled with enthalpy method to account for phase change in PCM. Systematic parametric studies are performed to understand the effect of mass flow rate, inlet charging system, storage system dimension and encapsulation of the shell diameter on the dynamic behaviour of the storage system. The overall effectiveness and transient temperature difference in HTF temperature in a cycle are computed for different geometrical and operational parameters to evaluate the system performance. It is found that the ability of the latent heat thermal energy storage system to store and release energy is significantly improved by increasing mass flow rate and inlet charging temperature. The transient variation in the HTF temperature can be effectively reduced by decreasing porosity.     

相变微胶囊悬浮液传热特性实验研究

相变微胶囊(microencapsulated phase change material,MPCM)在建筑节能领域应用广泛,为研究其传热特性,搭建了以水为换热流体(heat transfer fluid,HTF),微胶囊悬浮液为储能介质的潜热储能(latent thermal energy storage,LTES)系统。在实验过程中,通过改变换热流体的进口初始温度以及搅拌器的搅拌速率,获得了MPCM悬浮液的温度变化规律并计算了MPCM悬浮液的平均充放冷速率。实验结果表明:在充冷过程中,MPCM相变时温度变化速率减缓,相变温度区间较大,而在放冷过程中,MPCM相变时温度保持恒定,相变温度区间较小;未搅拌时,MPCM悬浮液中温度梯度较大,传热能力较差;搅拌时,MPCM悬浮液混合均匀,其温度梯度很小,传热能力较强;增加搅拌器的搅拌速率及水与相变微胶囊悬浮液的温差均可以提高MPCM的充放冷速率。