槽式太阳能集热与相变蓄热耦合模型(Ⅱ):性能优化

在采用两级组合相变蓄热材料的基础上,利用已建立的槽式太阳能集热单元和蓄热单元的1-2维混合模型,对组合相变材料蓄热性能进行优化研究。研究结果表明,受所选相变材料热物性的影响,随PCM1比例增大,蓄热速率减慢,总蓄热量增加;随传热流体质量流量增大,相变材料完全融化时间缩短,当质量流量大于0.5 kg/s后,质量流量对蓄热性能的影响减小;随相变材料初始温度升高,总蓄热量减小,熔化时间和达到最大蓄热量时间基本不变,对蓄热性能影响不大。     

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。     

泡沫铜强化石蜡相变蓄热特性的数值分析

通过构建泡沫金属内固液相变传热模型,对方腔蓄热单元中泡沫铜强化石蜡相变蓄热特性进行数值分析。数值模型采用考虑泡沫金属真实结构的等效导热系数通用模型,并兼顾石蜡在融化前后与金属骨架之间的热非平衡效应。通过求解模型得到方腔内石蜡固液界面演化规律与温度分布,进而对蓄热过程进行火用分析。结果表明:当前数值模型能较好地预测泡沫铜内固液相变传热;泡沫铜显著改善了石蜡相变的空间均匀性,减小了蓄热区温度梯度,使蓄热速率和火用效率得到有效提高。     

基于■理论的多级套管式相变蓄热系统优化

基于最小■耗散热阻原理,在考虑相变材料导热热阻以及非稳态传热过程的基础上,对多级套管式相变蓄热系统的融化温度进行了数值优化,获得了最优融化温度分布。在此基础上,研究了相变材料导热系数和传热管长度对最优融化温度、■耗散热阻和平均蓄热速率的影响。研究结果表明:与现有理论优化方法相比,提出的数值优化方法具有更好的适用性;优化后多级套管式相变蓄热系统可有效提高相变蓄热系统的平均蓄热速率,降低■耗散热阻;随着相变材料导热系数增大和传热管长度增加,多级套管式相变蓄热系统最优融化温度的温差愈加明显,其强化传热性能呈上升趋势。     

基于火积理论的多级套管式相变蓄热系统优化

本文基于最小火积耗散热阻原理,在考虑相变材料导热热阻以及非稳态传热过程的基础上,对多级套管式相变蓄热系统的融化温度进行了数值优化,获得了最优融化温度分布。在此基础上,研究了相变材料导热系数和传热管长度对最优融化温度、火积耗散热阻和平均蓄热速率的影响。研究结果表明,与现有理论优化方法相比,本文提出的数值优化方法具有更好的适用性;优化后多级套管式相变蓄热系统可有效提高相变蓄热系统的平均蓄热速率,降低火积耗散热阻;随着相变材料导热系数增大和传热管长度增加,多级套管式相变蓄热系统最优融化温度的温差愈加明显,其强化传热性能呈上升趋势。     

相变蓄热装置内部温度场的理论与实验研究

对螺旋盘管相变蓄热装置性能和相变材料 (PCM)的传热特性开展理论和试验研究,建立相变蓄热装置物理和数学模型,对蓄热温度场进行了数值模拟和实验测试。结果表明 ：自然对流换热对PCM的熔化过程影响很大,当考虑自然对流时,相变蓄热速率加快,相变分层现象明显;实验实测温度与模拟温度相近,说明所建立的模型适用于相变装置内部温度场的模拟。     

相变蓄热装置内温度场的模拟与实验研究

对螺旋盘管相变蓄热装置性能和相变材料(PCM)的传热特性开展模拟和实验研究,建立相变蓄热装置物理和数学模型,对蓄热温度场进行了数值模拟和实验测试。结果表明:自然对流换热对PCM的熔化过程影响很大,当考虑自然对流时,相变蓄热速率加快,相变分层现象明显;实验实测温度与模拟温度相近,说明所建立的模型适用于相变装置内部温度场的模拟。     

相变蓄热同心套管传热模型和性能分析

建立了一种简便的相变蓄热同心套管传热模型,用来求解相变材料在相变过程中流体温度和相变界面随时间和向位置的变化规律,模型中考虑了相变材料导热热阻和有效传热面积随时间和位置的变化,适用于流体入口温度和流量随时间变化的情况,计算值与有关文献值吻合,验证了模型的正确性。藉此模型对文献「７」中相变贮能换热器的储、放热性能进行了模拟分析。     

外压内吸薄壁弹性矩形阵列管相变蓄热装置放热研究

针对由于相变材料导热系数较低且易与受热面相剥离而造成相变蓄热装置放热功率不能满足工程实际需要的现象,设计了外压内吸薄壁弹性矩形阵列管相变蓄热装置。在外部正压和内部负压的共同作用下,采用薄壁弹性矩形阵列管可以解决相变材料与受热面相剥离的问题,同时提高了蓄热装置受热面的紧凑性。搭建相变蓄热实验台并测试蓄热装置在不同流体温度、不同流体流量和不同相变材料工作温度下的放热性能。研究结果表明:矩形管外侧流体流量越大,其传热系数和热功率越大,并且随着放热过程的持续进行,这两个参数的下降速率越小;相变蓄热装置的传热系数随着剩余热功率的下降而迅速降低,当剩余热功率占最大热功率的70%~80%时,传热系数下降速率出现转折,此后下降速率有所减小,当剩余热功率占最大热功率低于20%时,相变蓄热装置的放热过程基本结束;相变材料起始温度和相变蓄热装置进口流体温度的差值以及矩形管外侧流体流量变化时,蓄热装置的传热系数相差不大。     

壳管式相变蓄热器传热效率研究

设计了一套定量测试不同工况下壳管式相变蓄热器传热效率装置。采用壳管式相变储热,石蜡填充入壳管间,管内通入冷、热载流体,模拟吸热放热过程。测试发现:相同入口条件下,单位时间传热量随入口水温增加呈线性增加;管内载流体流量加大有助于提高传热水平,15~60 L/h流量内单位时间传热量增速随流量增加放缓;不同材质传热管单位时间传热量变化并不明显,表明管道热阻在相变蓄热器总热阻中所占份额较小;相同工况下的蓄热过程,热载流体由下向上流动传热形式明显优于由上向下管排形式;尝试在封装相变材料中添加金属网状结构,强化相变材料内部热传导速率,对比发现相同工况下相变材料中添加金属网状结构,可提高10%~15%左右传热量。     

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.     

Optimising PCM thermal storage systems for maximum energy storage effectiveness

A new performance parameter for PCM thermal storage systems, the energy storage effectiveness, is defined. This parameter can be used to optimise the design of any PCM thermal storage system to maximise the use of the thermal storage media. The paper presents results of a parametric study using an experimentally validated numerical model for PCM encapsulated in plates. The results are used to calculate the energy storage effectiveness which is ultimately used to optimise the useful energy that can be stored in the PCM thermal storage system. The energy storage effectiveness is also used to compare the useable storage capacity of the PCM relative to a sensible energy storage system.     

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.     

Segmented thermal storage

Standard methods of charging solar thermal energy into rock bed storage for space heating tend to reduce stratification because of decreasing collector temperatures in the afternoon. This creates inaccessible regions of higher temperature rocks and may reduce the amount of energy within the bed. Stratification of the segmented bed has the advantages of supplying the highest temperature air to the dwelling and the lowest temperature air to the collector. A method of preserving the stratification by segmenting the storage bed was numerically studied. Discharging was not studied.Segmenting a standard rock bed and routing the flow to segments cooler than the inlet air during charging was shown to preserve stratification throughout the bed. The simulated segmented bed contained 1% less maximum energy than an otherwise identical standard bed for an approximated solar day. This was a consequence of the segment control temperature locations.     

Latent heat storage

The investigations of materials presumably suitable as storage media for latent heat indicate that water, some salt hydrates and eutectic mixtures of water and salt hydrates possess extreme heats of fusion. Their melting points, ranging from about -50° to + 130°C, fit well for storing low grade heat in residential energy systems. Detailed experimental investigations on a large number of these media show, however, that only a few of them satisfy the quality requirments for practical application in storage units. Flexible flat-plate storage containers especially developed for selected salt hydrates which expand on melting also show satisfactory performance over long periods of operation. In the case of water and selected water-salt hydrate eutectics the volume increases on solidification, and the expansion of solid storage material, being very inhomgeneous, breaks even flexible containers after only a few storage cycles. This ruinous local expansion can be avoided, however, by adding a small amount of special, lower melting salt hydrate eutectics which homogenize the crystallization and solidification of the storage medium.     

蓄冷蓄热技术

简要介绍了蓄冷蓄热技术的应用与发展现状，归纳了蓄冷蓄热空调系统的原理和技术特点，提出了中央空调系统（包括采暖）采用蓄冷蓄热技术的诸多优势、宏观（社会）效益和微观（用户）效益以及对电网“移峰填谷”的重要作用；并例举出常州市金禧园生活小区蓄能中央空调系统运行情况的工程实例。     

Combined thermal storage

In this study a combination of the two basic storages, the water storage and the bed storage, is examined. Formulas and limitations of the combined storage process, for a specific geometrical shape, are presented and the exploitation of the thermal losses of the water storage is attempted.