夏季间歇运行工况下相变温度对相变回填地埋管换热器传热性能的影响

为探究相变温度对相变材料回填地埋管换热器传热性能的影响,建立管内流体换热、回填区域相变换热及土壤换热的三维耦合传热数值模型,利用焓-多孔介质模型对相变区域相变问题进行处理,研究夏季间歇运行工况下不同相变温度回填材料对埋管换热器传热性能的影响。结果表明:添加PCM,可有效提高换热量,短期内缓解埋管周围热积聚,利用相变温度18℃的PCM回填,单位井深换热量至少比普通材料回填提高49.54%;在间歇运行初期,换热量随相变温度的升高逐渐减小,低相变温度的PCM可明显改善埋管换热量,但随着时间的进行,较高相变温度PCM回填对换热器换热量的改善效果优于前期低相变温度。此外,在运行期间,不同相变温度的PCM表现出不同的熔化、凝固特性,当PCM的熔化、凝固过程交替进行时,可减缓土壤温度在运行期间内波动幅度。     

肋片增强式梯级相变储热系统放热特性的三维数值

梯级相变储热技术已被证明是解决相变材料导热性能差的重要方法。已有的关于梯级相变储热系统的数值研究通常是基于一维或二维数学模型完成的,大部分的研究聚焦于系统的储热过程。本工作设计了一种肋片增强型三管式梯级相变储能系统,并建立了三维数值模型。然后研究了系统放热过程中各级PCM的性能变化规律,探究了传热流体进口温度和PCM初始温度对系统放热速率的影响规律。结果表明,在放热过程中,各级PCM相变不会同时发生,受到储热材料的相变温度和潜热的影响最大。传热流体进口流速的增大会提高相变材料的放热速率,但随着流速的进一步增加,放热速率的提高程度明显减弱。相变材料的初始温度对显热放热过程具有一定的影响,但对于潜热放热阶段影响较小。     

不同结构组合式相变材料换热器性能分析

基于焓法建立可靠的相变传热模型,对采用单一相变材料的换热器及不同结构组合式相变材料换热器的相变传热过程进行数值分析.结果表明:组合式相变材料换热器的性能优于采用单一相变材料的换热器,特别是串联结构组合式相变材料换热器;不同结构组合式相变材料换热器中,流体不同入口速度对换热器性能对比具有较大影响;合理选择组合式相变材料各...     

复合相变储能材料的传热性能研究进展

总结近年来国内外相变储能材料的研究状况,包括相变储能材料的制备、传热性能、相变过程数值模拟和应用等,并对复合相变储能材料的传热性能研究方法的前景作了展望。     

纳米复合相变材料固液相变储能过程研究进展

对纳米复合相变材料固液相变储能过程的若干最新研究进行了回顾,从相变储能系统的动态性能和典型的凝固、熔化传热过程两方面总结了相关研究的进展,并重点评述了数值模拟研究中纳米复合相变材料有效热物性预测方法的适用性及其与实验结果之间的偏差,最后对纳米复合相变材料固液相变储能过程的未来发展和重点研究方向进行了展望。     

State-of-the-art development of numerical simulations of phase change materials based systems

相变储能材料是近年来热能储存领域研究的热点,绝大多数相变储能材料系统的相变过程是高度非线性变化的,难以求得解析解。本文分别介绍了基于Ansys-Fluent、Ansys、PCMexpress软件在建筑节能等不同领域对相变储能材料非线性相变过程进行数值分析和研究的发展现状,并展望了PCM数值分析的发展方向。首先通过综述指出了数值分析在PCM系统研究和应用中处理非线性相变问题的独特优势,这为PCM系统研究及应用过程中处理热量传递中瞬态相变及模拟工程应用提供了有效手段。随后对比分析了Fluent、Ansys、PCMexpress的模拟研究应用情况、各自特点,指出了其中存在的模型建立、初始条件、可靠性等问题。最后结合相变储能材料发展中存在封装及无机PCM系统过冷、相分离的问题,指出了PCM系统数值分析可能朝着建立合理模型、验证模拟结果、改进数值模拟软件、与实际问题结合、拓展应用领域等方向发展,以及其在PCM系统研究和应用中具有的广阔前景。     

相变材料应用于墙体的数值传热研究

分析相变材料的特点和相变墙体传热理论研究与应用现状,指出相变墙体材料的研制方向。对不同构造相变墙体建立了传热理论模型,采用显热容法运用数值模拟方法模拟了在周期性变化的室外边界条件下,相变储能墙体内的传热过程及墙体内表面的温度变化。计算结果表明:储能墙体中的相变材料层是影响墙体传热的重要因素之一。     

多级并联相变管壳式换热器传热性能分析

在管壳式换热器中并联填充多级相变材料或填充单相变材料,比较两种传热装置的传热性能,分析相变材料在两种换热器的换热过程中的熔化特性、换热速率。结果显示：对于相变材料三级并联填充的换热器,相变材料完全熔化时间沿换热内管（热工质流体）轴心往外逐渐增加;在所有相变材料均完成相变之前,其三级并联相变材料的熔融前沿呈曲线状;相变材料三级并联填充的换热器的最高换热速率是单相变材料填充的1.03倍;热工质流体入口温度不变时,增加热工质流体流量可以在一定限度上增加相变材料三级并联填充的换热器的换热效率;但热工质流体流量过大会在一定限度上降低相变材料三级并联填充的换热器的换热效率。     

高温相变蓄热的研究进展

从如下两个方面总结了高温相变蓄热的研究现状：①在高温相变材料(PCM)方面，重点介绍了高温相变材料的一些重要性能及其测量，高温相变材料的封装，高温复合相变材料及高温相变材料的应用；②在传热分析方面，主要介绍了相变过程的数值模拟和相变蓄热系统(LTES)的热力学优化。     

管内流体流动管外PCM发生相变的贮能系统热性能研究

建立了分析空调贮能系统中管内流体流动管外PCM发生相变的相变的贮能器热性能的数学模型，并进行了数值计算。其中，把传热流体看作是沿轴向的—维无粘流动，对PCM相变过程的求解用显热容法。计算结果与文献中的计算结果吻合较好。所得结论对该类贮能系统的设计和性能优化有一定指导作用。     

Estimation of storage costs for large hydrogen storage facilities

The paper presents an economic evaluation of alternative hydrogen storage methods (pressurized gas, metal hydride and cryogenic storage) for large stationary (utility-scale) applications. The presentation of cost calculation clarifies the importance and influence of a set of relevant parameters depending on the charging-discharging schedule, the relation of the capacity to power level etc. The results presented define the useful range of application for each storage method, whereas the corresponding cost composition (power related capital costs, capacity-related capital costs, energy costs) is analysed and discussed.     

A storage tank for vehicular storage of liquid hydrogen

This article outlines a concept for a new method of fabricating cryogenic liquid hydrogen storge tanks with emphasis on the application of liquid hydrogen as an automotive fuel. It includes a recapitulation of the properties of hydrogen and gasoline for reference, a discussion of automotive fuel utilisation rates, a thermal analysis of the liquid hydrogen boil-off rate for a reference storage container and the new concept tank. In addition, an analysis of the tank concept and its method of assembly line fabrication are provided. The conclusions reached are that this fabrication concept would provide a liquid hydrogen storage tank of improved thermal performance, that the tank could be potentially less expensive to build than current technology tanks, and that the tank would be suitable for automotive containment of liquid hydrogen.     

The United States of storage [electric energy storage]

The collaboration between the states and the DOE's Energy Storage Research Program is proving to be an outstanding success. The selected projects show a good portfolio of advanced energy storage media: a ZnBr flow battery, the NaS battery, supercapacitors, and flywheels. The applications are equally varied: mitigation of substation congestion, grid frequency control, load management, and stabilization of a microgrid. The goal of these partnerships with the states is to demonstrate electric energy storage as a technically viable, cost-effective, and broadly applicable option for increasing the reliability of the electricity system and for electric energy management.     

Large-scale compressed hydrogen storage as part of renewable electricity storage systems

Storing energy in the form of hydrogen is a promising green alternative. Thus, there is a high interest to analyze the status quo of the different storage options. This paper focuses on the large-scale compressed hydrogen storage options with respect to three categories: storage vessels, geological storage, and other underground storage alternatives. In this study, we investigated a wide variety of compressed hydrogen storage technologies, discussing in fair detail their theory of operation, potential, and challenges. The analysis confirms that a techno-economic chain analysis is required to evaluate the viability of one storage option over another for a case by case. Some of the discussed technologies are immature; however, this does not rule out these technologies; rather, it portrays the research opportunities in the field and the foreseen potential of these technologies. Furthermore, we see that hydrogen would have a significant role in balancing intermittent renewable electricity production.     

Analysis of the current energy storage market and energy storage economy

储能在未来电网以及可再生能源的应用中将起到至关重要的作用.它的应用范围涉及发电,传输,分配乃至终端用户.本文简要分析并总结了储能市场的经济性,重点阐述了储能应用的主要瓶颈问题----成本.通过分析与计算,确定了储能产品的目标成本,并且以历史上光伏产业规模效应的经验曲线为基础分析了能够降低储能成本的可行途径.储能应用市场将为传统能源结构带来根本性的变化,给社会经济带来巨大的福利,它的应用势在必行.但是,要实现储能的大规模应用还有诸多艰巨的任务与挑战,其中最重要的是要降低储能系统的成本,而实现这个目标需要多方面的共同努力.     

Effect of storage thermal behavior in seasonal storage solar heating systems

An analytical methodology has been developed to investigate the effects of storage operational strategies (or, equivalently, stratification) on the performance of a seasonal storage solar heating system with a water storage. The method is based on a relative comparison between a thermally stratified and well-mixed storage system representing probable extreme outcomes of the subsystem-to-storage loop control strategies. The effects are incorporated into a set of performance reduction factors that describe maximum changes in the solar collector yield, storage losses and solar fraction due to storage operational mode. The study indicates that the storage thermal behavior could in the worst case affect the yearly solar fraction by a factor of 2, but most likely a maximum value from 1.35 to 1.6 could be expected.     

Comparative study of internal storage and external storage absorption cooling systems

This work presents a comparative study of the performance of absorption cooling systems with internal storage and with external storage. A full dynamic simulation model including the solar collector field, the absorption heat pump system and the building loads has been performed. The first system is composed by four heat pumps that store energy in the form of crystallized salts so that no external storage capacity is required. The second one is a conventional system composed of one liquid absorption pump and external storage in a water tank. Many batteries of simulations have been done to evaluate the performance of these cooling machines when varying solar field surface, solar collector’s efficiency curve and the storage capacity of the systems. Two different indices have been calculated to analyze the response of both systems: Solar Fraction and Primary Energy Ratio. The comparison between both absorption chillers indicates that in order to reach similar values of storage energy, conventional system has a greater room requirement than four units with internal storage working in parallel, requiring an external water tank of at least 15 m³.     

Impact of refueling parameters on storage density of compressed hydrogen storage Tank

Hydrogen fuel cell vehicle (HFCV) is one of the key contributors to sustainable development of the society. For commercial deployment and market acceptability of fuel cell vehicles, efficient storage of hydrogen with an optimum refueling is one of the important challenge. Compressed hydrogen storage in Type IV tanks is a mature and promising technology for on-board application. The fast refueling of the storage tank without overheating and overfilling is an essential requirement defined by SAE J2601. In this regard, station parameters such as hydrogen supply temperature, filling rate and vehicle tank parameters such as filling time strongly influences the storage capacity of the tank, affecting driving range of the fuel cell vehicle. This paper investigates the impact of these parameters on storage density of the tank defined in terms of state of charge. For this, refueling simulation based on SAE J2601 protocol has been performed using computational fluid dynamic approach to investigate the influence of station parameters on storage density of the tank. Further, the root cause analysis was carried out to investigate the contribution of station and vehicle tank parameters for enhancing the storage density of the tank. Finally, the regression model based on these refueling parameters was developed to predict the density attained at different filling conditions. The results confirmed the strong contribution of pressure, filling time, supply temperature and least contribution of temperature, filling rates in enhancing the storage density of the tank. The results can provide new insight into refueling behavior of the Type IV tank for fuel cell vehicle.     

氢存储技术

日益严峻的能源危机和环境污染，使得发展清洁的可再生能源成为各个国家的重要议题。氢能源以其可再生性和良好的环保效应成为未来最具发展潜力的能源载体。氢的储存是发展氢能技术的难点之一。文章介绍了高压、液化、金属氢化物和碳质吸附等储氢技术的研究现状，并对储氢技术的发展趋势进行了讨论。