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。     

基于相变材料的储热器及其传热强化研究进展北大核心CSCD

相变储热是具有广阔应用前景的储能技术之一,具有储热密度大、相变温度稳定等优点,但相变材料的热导率低制约了相变储热技术的发展。提升相变材料的热导率和储热器件的传热速率是有效的解决途径。针对相变材料热导率强化研究进展有大量综述,而对于储热器件层面的传热强化的总结较少,本文回顾了近10年国内外在储热器及其传热强化研究方面的进展。为适应不同应用需求,不同类型的相变储热器应运而生,根据储热器的工作模式和结构可以分为管壳式、填充床式、板式、热管式4类,本文系统地介绍了4类储热器的工作原理、优缺点以及强化传热研究,主要比较了结构优化后的储热器与传统储热器的传热速率和储/放热性能,结果指出对储热器的内部结构进行改进及拓展外部结构等方法能有效增加储热容量和储/放热速率,对于提高系统相变储热能力具有积极作用,分析表明后续的研究应该明晰储热器内部多相耦合传热机制,增强储热器对动态工况适应能力,拓宽应用范围。     

储热用高温相变复合材料

采用陶瓷技术将碳酸盐共熔物储热介质与陶瓷基体复合在一起，制成一种新的高温相变复合材料。这种复合材料的致密度和高温相变潜热分别达到了理论值的９０％和７０％，使用温度可以达到８００℃。在３００￣８００℃温度范围内，储热量为７４３．２ｋＪ／ｋｇ。探讨了熔烧温度、保温时间、成形压力、原材料和添加剂的影响。系统的基本组成是Ｎａ２ＣＯ３＋ＢａＣｏ３＋ＭｇＯ。     

变速运动相变胶囊强化传热实验研究

为了研究变速运动对相变胶囊的强化传热效果,选用十六烷为相变材料,黄铜为壳制备圆柱形相变胶囊,利用曲柄摇杆往复装置实现变速运动并搭建实验平台;实验设计相变胶囊在蓄、放热过程中温度的变化范围为10～30℃,变速运动的方向为沿胶囊轴向或径向往复运动,振幅为6～12.5 mm,频率为1.55～3.78 Hz,通过测量均匀分布在胶囊内部轴线上8个测点的温度数据分析变速运动的方向、振幅和频率对胶囊蓄、放热效果的影响。实验结果表明：变速运动显著增强了相变胶囊的换热效果,在实验范围内,相比于静止状态,换热系数最大可增加35.6%;胶囊沿径向运动比沿轴向运动强化换热效果更好,沿径向运动时换热时间最多可缩短26.7%;不同工况下胶囊的放热时间均高于蓄热时间,增加振幅和频率可以有效提高蓄、放热效率且对蓄热过程的影响更加显著。     

组合式相变材料组分配比与储热性能研究

采用焓法对组合式相变材料(PCM)储热系统的相变过程进行了数值计算,分析了组合式相变材料中各个PCM组分质量分数的变化对系统储热性能的影响。结果表明,对于组合式相变材料储热系统,存在着最优组分配比,使得系统的储热性能达到最佳。     

相变储热研究进展及综述

清洁能源大多存在固有的间歇性和波动性,可能导致能源供应和能源消费之间的不平衡。储能是必不可少的,相变储能具有熔融凝固循环温度恒定,相对较高的能量密度,体积小,控制相对容易,安全可靠等优点。并针对相变材料的分类、相变储能系统强化传热技术、相变储能技术应用等方面进行了综述。     

潜热储能系统的传热及热力学优化研究

介绍了相变潜热储能系统的组成,特点及其传热和热力学优化研究。     

固—液相变蓄热强化传热的实验研究

石蜡是良好的盯变蓄热材料（ＰＣＭ）,没有相分离和过冷现象。本文描述了以石蜡为蓄热材料,对单盘管和双盘管蓄热器进行的蓄、放热实验研究。结果表明：在类似的实验条件下,双盘管蓄热器增加了７０％传热面积,可以将一个蓄／放热循环的时间减少到大约为单盘管蓄热器的１／３。     

偏心分形翅片管相变储热单元性能强化模拟北大核心CSCD

为了探索偏心分形翅片管对相变储热单元性能强化的作用机理,对偏心分形翅片管相变储热单元中石蜡的熔化展开了二维非稳态模拟研究。在考虑自然对流的情况下对比研究了偏心矩形翅片和偏心分形翅片两种储热单元的传热特性。并对偏心分形翅片结构进行了局部强化,选择矩形翅片、Y型翅片和分型翅片3种方案。结果表明,偏心分形翅片结构对自然对流的促进高于偏心矩形翅片结构且整体温度分布更均匀,这与分型翅片可以促进热量由点到面的扩散相符。在3种局部强化方案中,偏心分形翅片强化效果最佳,且整个过程的熔化速率都有提高,使熔化时间缩短了70%。这对管壳式相变蓄热器的性能提升提供了很好的理论指导,进一步扩展了其在储能领域的应用前景。     

Performance enhancement in latent heat thermal storage system: A review

Phase change material (PCM) based latent heat thermal storage (LHTS) systems offer a challenging option to be employed as an effective energy storage and retrieval device. The performance of LHTS systems is limited by the poor thermal conductivity of PCMs employed. Successful large-scale utilization of LHTS systems thus depends on the extent to which the performance can be improved. A great deal of work both experimental and theoretical on different performance enhancement techniques has been reported in the literature. This paper reviews the implementation of those techniques in different configurations of LHTS systems. The influence of enhancement techniques on the thermal response of the PCM in terms of phase change rate and amount of latent heat stored/retrieved has been addressed as a main aspect. Issues related to mathematical modeling of LHTS systems employing enhancement techniques are also discussed.     

Numerical simulation of a multi-layer latent heat thermal energy storage system

A computational model for the prediction of the thermal behaviour of a compact multi-layer latent heat storage unit is presented. The model is based on the conservation equations of energy for the phase change material (PCM) and the heat transfer fluid (HTF). Electrical heat sources embedded inside the PCM are used for heat storage (melting) while the flow of an HTF is employed for heat recovery (solidification). Parametric studies are performed to assess the effect of various design parameters and operating conditions on the thermal behaviour of the unit. Results indicate that the average output heat load during the recovery period is strongly dependent on the minimum operating temperature, on the thermal diffusivity of the liquid phase, on the thickness of the PCM layer and on the HTF inlet mass flowrate and temperature. It is, on the other hand, nearly independent of the wall thermal diffusivity and thickness and of the maximum operating temperature. Correlations are proposed for the total energy stored and the output heat load as a function of the design parameters and the operating conditions. © 1998 John Wiley & Sons, Ltd.     

Enhancing the thermal response of latent heat storage systems

Latent heat storage systems especially those employing organic materials have been reported to exhibit a rather slow thermal response. This is mainly due to the relatively low thermal conductivities of organic latent heat materials. This paper reports experiments carried out to investigate methods of enhancing the thermal response of paraffin wax heat storage tubes by incorporation of aluminium thermal conductivity promoters of various designs into the body of the wax. Heating and cooling runs were carried out and phase change times determined. It was found that the phase change time reduced significantly by orders of up to 2·2 in energy storage (heating) and 4·2 in energy recovery (cooling). Internal fins performed much better than the star matrices and expanded aluminium performed better than promoters made from aluminium sheet metal in both storage and recovery of heat. © 1997 John Wiley & Sons, Ltd.     

The correlation between the number of fins and the discharge time for a finned heat pipe latent heat storage system

The concept of a solar energy heat pipe latent heat storage system is presented. In order to assure large charging and discharging rates, finned heat pipes are used to transfer heat to and from the phase-change material (paraffin in this case). The evolution of the solid - liquid interface is studied by considering the radial heat transfer (due to the heat pipe wall) and the angular one (due to the fin). Two mathematical models, corresponding to exponential, respectively polynomial functions describing the fin temperature profile are presented and the results are compared. The two models allow the evaluation of the discharge time of the storage unit for a certain number of fins for a single heat pipe. When the discharge time has a fixed value, the methods presented in the paper allow to conclude whether the number of fins is sufficiently large to assure the complete solidification of the phase-change material.     

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。     

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。     

内通流体套管式潜热蓄热器充放热过程的实验分析

通过建立与工业实际相似的加肋同心套管式潜热蓄热器模拟实验台，对潜热蓄热器内通流体时的充热、放热过程进行了实验研究。实验得出了流体的出口温度、充热量和放热量随时间的变化规律。     

Cascaded latent heat storage for parabolic trough solar power plants

The current revival of solar thermal electricity generating systems (SEGS) unveils the still existing need of economic thermal energy storages (TES) for the temperature range from 250 °C to 500 °C. The TES-benchmark for parabolic trough power plants is the direct two tank storage, as it was used at the SEGS I plant near Barstow (USA). With the introduction of expensive synthetic heat transfer oil, capable to increase the operating temperature from former 300 °C up to 400 °C, the direct storage technology became uneconomical. Cascaded latent heat storages (CLHS) are one possible TES alternative, which are marked by a minimum of necessary storage material. The use of a cascade of multiple phase change materials (PCM) shall ensure the optimal utilization of the storage material.This paper reports experimental and numerical results from the investigation of cascaded latent heat storages with alkali nitrate salts like NaNO₃, KNO₃ and others more. The experiments were conducted with vertical shell and tube type heat exchanger devices under realistic operation parameters. The experimental results were used for a numerical model to simulate different CLHS configurations. Dymola/Modelica was used to conduct the simulation. The outcome of this work shows on the one hand, that the design of CLHS for this temperature range is more complex than for the temperature range up to 100 °C. And on the other hand, the low heat conductivity of available PCM is an obstacle which must be overcome to make full use of this promising storage technology.     

HVAC领域相变贮能研究的现状与进展

总结了相变传热的特点及求解方法 ;相变墙板的研制以及使用效果方面的研究现状 ;相变在供暖、空调系统中的应用 ;相变贮能技术在HVAC中应用的诸多优势。提出了HVAC领域相变贮能技术今后的研究方向。     

Evaluating the performance of forced convection heat transfer enhancement

Two methods for assessing thermal performance were evaluated for four kinds of forced convective heat transfer augmentations. On method uses the first law of thermodynamics, i.e., the heat transfer improvement at (1) constant Reynolds number, (2) constant pressure loss, and (3) constant pumping power. The other method uses the second law of thermodynamics, i.e., the entropy generation. The first method restricts the effective region and the second method supplies the condition for achieving the minimum entropy generation rate. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(2): 142–154, 1998