板式相变贮能换热器传热模型和热性能分析

建立了板式相变贮能换热器的无量纲传热模型。它对流体入口流量、入口温度随时间变化情况和需考虑入口效应及添加肋片的情况均适用。模型解和文献准稳态解吻合。作为算例,藉此模型从各时刻的流体温度、相变界面随空间的分布情况和相变蓄热比、相变传热效率、传热系数、完全相变截面位置随时间的变化情况六个角度分析了一板式相变贮能换热器的相变传热性能。该模型可为板式相变贮能换热器的结构优化设计和热性能分析提供帮助。     

内通传热流体的圆管外相变材料的无量纲储传热准则的研究

建立了分析内通传热流体的圆管外相变材料储,储热特性的理论模型,并提出分析瞬态相变层厚度分布,传热流体轴向温度分布及圆管相变材料储,传热量的新方法：温度－固液界面移动交替迭代法,通过理论分析和数值计算,得到确定上述参数的无量纲公式,公式与数据点的平均拟合精度分别为０．３％、１．６２％和２．５％。准则公式计算值与相同条件下的文献值吻合,验证了本文模型、方法和结果的正确性。所得的无量纲公式不局限于某一种     

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。     

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。     

蓄热式管壳换热器传热特性研究

针对热电联产机组供热期发电负荷受供热量限制,机组调峰能力下降、电力系统弃风弃光现象严重的问题,设计了一种新型蓄热式管壳换热器。利用相变材料蓄/放热过程中温度接近恒定、释放潜热量大等优点,选取石蜡为相变材料,换热器相变区作为换热单元,采用控制变量法,针对传热流体流速、相变材料导热系数及相变层厚度等关键因素,对换热单元的蓄/放热过程进行数值模拟。结果表明:提高传热流体流速可增强换热单元蓄热能力,缩短相变材料完全熔化时间,放热过程中为保证换热器输出端热量,应适当选取传热流体流速;使用复合材料提高相变材料导热系数能够增强换热单元的换热能力,在相同传热流体流速下使换热单元平均传热系数较纯石蜡工况提升2倍以上;增加相变层厚度在放热过程中可延长传热流体出口温度维持的时间。     

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。     

含相变材料双层玻璃窗光热分析模型

建立了含相变材料双层玻璃窗的光热传输模型,考虑相变材料和玻璃半透明特性,采用有限差分求解方程。在通过实验数据验证模型准确的基础上,分析了相变材料的融化温度对含相变材料双层玻璃窗光热性能的影响。结果显示:建立的模型可模拟相变材料双层玻璃窗的光热传输过程;随融化温度升高,含相变材料双层玻璃窗温度衰减因子则逐渐增大,相变材料融化时间延后,相变材料呈液态的时间变短,但温度滞后值、热流密度和太阳透射能则呈不规则变化。     

新型定形板状相变材料的蓄/放热特性

对填充了新型定形板状相变材料的蓄热槽的蓄／放热特性进行了数值计算分析和实验比较。根据数值计算，对影响蓄热槽蓄／放热特性的主要因素——相变材料的几何尺寸、相变材料的导热系数、流体流速、对流放热系数、相变材料填充率等的影响规律进行了分析研究，计算出了蓄热槽内温度分布随时间的变化；并在实验台上测试了蓄热槽初始温度、流人和流出蓄热槽流体温度、作为蓄热体的相变材料测点温度随时间的变化，计算结果与实验结果具有较好的一致性。     

相变微胶囊功能流体相变区间的影响因素和变化趋势分析

相变微胶囊功能流体所具有的相变区间是影响其强化传热效应和工程应用价值的主要因素。采用双流体数学模型通过数值模拟发现:在层流条件下,双流体模型能够很好地模拟颗粒相体积分数、管径和R e对相变区间的影响。功能流体的相变段长度和总吸热量都随着这三个因素的增大而显著增大。同时相变段长度还取决于入口温度和边界条件等因素。以直链烷烃为相变材料的功能流体在相变段的蓄热能力相近。但在同R e下,功能流体的相变段长度和总吸热量都随着囊芯材料相变温度的升高而减小。入口温度是影响相变材料熔化速度的重要因素。相变段的长度、总温升和总吸热量与流体入口过冷度都呈线性关系。在第一类边界条件下,相变段长度与壁面过热度呈指数为负的幂指数关系,而相变段总温升和总吸热量都随壁面过热度的增大而增大。     

板式石蜡储热器传热的数值模拟

在相变储热器中采用强化传热技术，克服相变材料的低导热性能，是目前国内外研究的热点。应用FLUENT软件数值模拟了翅片强化板式石蜡储热器的凝固传热过程，得到随时间变化的相界面位置、总凝固时间、壁面热流、翅片温度分布等，并进一步分析了翅片对不同长宽比叫的储热器的强化传热效果。模拟结果表明，只有当ω≥1时，翅片才能对储热器起到明显的强化传热作用，研究结果可为相变储热器的优化设计提供可靠的依据。     

正交各向异性相变材料的无网格法传热模型及应用

利用无网格迦辽金（EFG）法建立正交各向异性相变材料的传热计算模型,基于该模型编程完成各向异性材料太阳能相变蓄热水箱和管壳式相变蓄热单元的相变传热分析,并探讨热导率因子和材料方向角对复合材料相变传热特性的影响。研究表明：在相同节点布置下EFG法的温度场和相界面计算精度均高于有限元法,EFG法在动态相界面追踪方面具有明显优势。增大热导率因子并减小材料方向角可有效增强复合相变材料传热性能,加快相变速度,提高太阳能相变储能装置的蓄/放热效率。对于各向异性材料太阳能相变蓄热水箱和管壳式相变蓄热单元,热导率因子和材料方向角的合理取值范围分别为4~6和0°~15°。     

Thermal Performance of a Phase Change Material‐Based Latent Heat Thermal Storage Unit

An experimental analysis is presented to establish the thermal performance of a latent heat thermal storage (LHTS) unit. Paraffin is used as the phase change material (PCM) on the shell side of the shell and tube‐type LHTS unit while water is used as the heat transfer fluid (HTF) flowing through the inner tube. The fluid inlet temperature and the mass flow rate of HTF are varied and the temperature distribution of paraffin in the shell side is measured along the radial and axial direction during melting and solidification process. The total melting time is established for different mass flow rates and fluid inlet temperature of HTF. The motion of the solid–liquid interface of the PCM with time along axial and radial direction of the test unit is critically evaluated. The experimental results indicate that the melting front moves from top to bottom along the axial direction while the solidification front moves only in the radial direction. The total melting time of PCM increases as the mass flow rate and inlet temperature of HTF decreases. A correlation is proposed for the dimensionless melting time in terms of Reynolds number and Stefan number of HTF. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21120     

水平管壳式相变蓄热装置的强化传热研究

基于焓法模型对水平管壳式相变蓄热装置热性能的增强进行研究,首先分析蓄热过程中传统管壳式装置内材料的传热及流动机理;然后引入椭圆元素并对比椭圆内管及外壳的强化传热效果;最后对热源温度、相变材料导热系数及初始温度对装置热性能的作用规律进行探讨。结果显示,椭圆外壳的强化传热效果优于内管,同等条件下,长短轴之比为2的椭圆外壳可使蓄热时间缩短53.5%。热源温度升高,椭圆外壳的强化传热效果进一步增强,相变材料的导热系数及初始温度对装置热性能的影响较小。     

Numerical and experimental investigation for heat transfer in triplex concentric tube with phase change material for thermal energy storage

This paper addresses a numerical and experimental investigation of a thermal energy storage unit involving phase change process dominated by heat conduction. The thermal energy storage unit involves a triplex concentric tube with phase change material (PCM) filling in the middle channel, with hot heat transfer fluid (HHTF) flowing outer channel during charging process and cold heat transfer fluid (CHTF) flowing inner channel during discharging process. A simple numerical method according to conversation of energy, called temperature & thermal resistance iteration method has been developed for the analysis of PCM solidification and melting in the triplex concentric tube. To test the physical validity of the numerical results, an experimental apparatus has been designed and built by which the effect of the inlet temperature and the flow rate of heat transfer fluid (HTF, including HHTF and CHTF) on the thermal energy storage has been studied. Comparison between the numerical predictions and the experimental data shows good agreement. Graphical results including fluid temperature and interface of solid and liquid phase of PCM versus time and axial position, time-wise variation of energy stored/released by the system were presented and discussed.     

壳管式相变储能换热器性能研究与场协同效应分析

建立壳管式相变储能换热器仿真模型,利用Fluent软件对蓄能、释能工况分别进行模拟。从温度场、速度场、固液交界面3个方面分析逐时换热强度的变化原因;探讨在蓄热过程中热源管壁温、热管口径规格对传热效率的影响。研究结果表明:蓄热工况下管间热扰及自然对流作用明显,10000 s时液相分数达到95%。放热工况以导热为主,60000 s时相变材料仅凝固了75%。从场协同效应分析,采用小尺寸热源管能缩短时间,但单位面积换热强度有明显下降。换热温差≤20℃时,其强化效果开始衰弱。     

Experimental and numerical investigation of thermal energy storage with a finned tube

A latent heat thermal energy storage system using a phase change material (PCM) is an efficient way of storing or releasing a large amount of heat during melting or solidification. It has been determined that the shell‐and‐tube type heat exchanger is the most promising device as a latent heat system that requires high efficiency for a minimum volume. In this type of heat exchanger, the PCM fills the annular shell space around the finned tube while the heat transfer fluid flows within the tube. One of the methods used for increasing the rate of energy storage is to increase the heat transfer surface area by employing finned surfaces. In this study, energy storage by phase change around a radially finned tube is investigated numerically and experimentally. The solution of the system consists of the solving governing equations for the heat transfer fluid (HTF), pipe wall and phase change material. Numerical simulations are performed to investigate the effect of several fin parameters (fin spacing and fin diameter) and flow parameter (Re number and inlet temperature of HTF) and compare with experimental results. The effect of each variable on energy storage and amount of solidification are presented graphically. Copyright © 2005 John Wiley & Sons, Ltd.     

Heat transfer enhancement in medium temperature thermal energy storage system using a multitube heat transfer array

An experimental energy storage system has been designed using an horizontal shell and tube heat exchanger incorporating a medium temperature phase change material (PCM) with a melting point of 117.7 °C. Two experimental configurations consisting of a control unit with one heat transfer tube and a multitube unit with four heat transfer tubes were studied. The thermal characteristics in the systems have been analysed using isothermal contour plots and temperature time curves. Temperature gradients along the three directions of the shell and tube systems; axial, radial and angular directions have been analysed and compared. The phase change in the multitube system was dominated by the effect of convective heat transfer compared to conductive heat transfer in the control system. The temperature gradient in the PCM during phase change was greatest in the radial direction for both the control and multitube systems. The temperature gradients recorded in the axial direction for the control and multitube systems during the change of phase were respectively 2.5 and 3.5% that of the radial direction, indicating essentially a two-dimensional heat transfer in the PCM. The onset of natural convection through the formation of multiple convective cells in the multitube system significantly altered the shape of the solid liquid interface fluid flow and indicates the requirement for an in-depth study of multitube arrangements.