蓄冷球凝固的FLUENT数值模拟研究

利用计算流体力学软件FLUENT凝固／熔化模型对一种相变材料蓄冷球的凝固过程进行数值模拟研究,得到了在第一类边界条件下蓄冷球凝固过程的温度场分布,相界面移动规律,并分析了凝固时间与壁面温度和球径的关系。本文所得到的结论对相变问题的数值模拟以及相变蓄能装置的设计具有重要的参考价值。     

蓄能互联热泵系统相变装置熔化与凝固过程特性分析

介绍了一种新型的蓄能互联热泵系统。利用数值模拟的方法对填充石蜡C17的球型蓄热单元的熔化与凝固过程进行研究,分析了球壁温度、相变单元尺寸和相变材料初始温度三种影响因素对熔化过程和球壁温度对凝固过程的影响。通过对两个过程对比发现相变单元尺寸对相变过程影响最大,在相同温差条件下完全熔化时间少于完全凝固时间,熔化过程中始终存在的石蜡-壁面与液相石蜡-固相石蜡之间的对流换热过程增加了熔化速率。     

蓄冷球在流场中凝固过程的数值模拟

通过CFD软件模拟了单个共晶盐蓄冷球在蓄冷槽中的凝固过程.在整个充冷过程中蓄冷球表面与外围载冷剂流场换热直至完全凝固.模拟中发现,由于整个流场的流速较低,蓄冷球凝固初始阶段球表面的自然对流对流场的影响不可忽视,同样也影响球体本身的热通量.模拟结果表明蓄冷球在负向流动流场中所需的凝固时间小于正向的凝固时间.     

相变蓄冷装置内传热及相变特性研究

建立了三种不同蓄冷球球径堆叠方式的相变蓄冷装置模型,对其进行了数值模拟以研究其内部传热及相变特性。结果表明：随着流速的提高、蓄冷球直径的减小,蓄冷结束后三种方案中装置内蓄冷球的凝固率提升显著;双球径方案与单球径方案装置内蓄冷球凝固率随时间变化的规律在蓄冷过程初段相类似,但两方案中相同球径部分蓄冷球相变结束,双球径方案中发生相变的蓄冷球由大直径转变为小直径时,其凝固率随时间变化的速度逐渐超过单球径方案。该研究可为相变蓄冷装置的实际设计及性能优化提供参考     

加快推进抽水蓄能行业标准体系建设

抽水蓄能是新型电力系统的重要组成部分,在"双碳"目标下,抽水蓄能的发展迎来了黄金期,随着国家相关配套政策的落地,抽水蓄能行业将出现井喷式发展,探索适应新形势下的抽水蓄能行业标准体系建设势在必行.本文详细阐述了抽水蓄能行业标准化建设现状及对新型电力系统的关键作用,并对建立完备的抽水蓄能标准体系提出建议,最后通过展望为学者研判该研究的发展趋势提供参考.     

新能源的开发与热泵技术的应用

从开发新能源的角度出发,叙述了热泵技术原理及其蓄能的意义。对一般商业用电、常规中央空调用电与蓄能中央空调的用电在24h之内的分布状况进行了比较分析,得出了实行峰谷电价,蓄能才有意义;不搞蓄能,不能完全使用低谷电价;蓄能可以削峰填谷,减少装机容量,节省费用45％以上的结论。     

变速抽水蓄能发电电动机电磁设计与试验研究

根据变速抽水蓄能发电电动机的运行原理、等效电路以及功率传输特性,对10MW变速抽水蓄能发电电动机进行了电磁设计,确定了10MW变速抽水蓄能发电电动机的主要结构尺寸;建立了变速抽水蓄能发电电动机二维电磁场的数学方程和物理模型,对变速抽水蓄能发电电动机电磁场数学方程进行了计算,分析了变速抽水蓄能电机在发电机工况下亚同步速时磁力线和气隙磁密的分布情况,确定了在发电机工况下亚同步速时定子电压波形和定子电流波形,研究了定子铁芯损耗和转子铁芯损耗的分布规律;根据电磁设计参数加工制造了10MW变速抽水蓄能发电电动机样机,搭建试验测试平台,将试验测试结果和计算结果进行对比,验证了电磁设计方案的可行性和计算结果的准确性,为更大容量变速抽水蓄能电机的研究奠定了基础.     

能量地下蓄存及其传热效能分析

储能技术是实现能源可再生化和高效利用的一种有效途径,提高其综合利用率和实现能源的实时补充。着重论述地下蓄能技术发展状况和面临的研究问题,并通过实验和模拟计算,对蓄能的传热作用进行了分析和探讨,指出蓄能改变地下蓄能体的能位,并表现为蓄能体温度和分布的变化,这种变化随时间而改变。建议进一步开展完善地下蓄能理论研究,推动中国地下蓄能技术的发展。     

海水抽水蓄能技术发展现状及应用前景CSCD

抽水蓄能技术是目前广泛应用的大规模储能技术之一,传统抽水蓄能技术需要特殊的地理条件建造两个水库,投资成本高、破坏生态环境,并且对淡水资源依赖严重。海水抽水蓄能技术利用海洋作为上水库或下水库,水位变幅小,减少了水库建设及其投资成本,解决了传统抽水蓄能电站对淡水资源的利用问题以及环境破坏问题,对于临海和淡水资源缺乏的岛国和城市具有非常广阔的发展前景。本文介绍了海水抽水蓄能系统的工作原理,全面分析了海水抽水蓄能系统的研究进展和应用情况,总结了开发海水抽水蓄能系统存在的技术与应用问题,并对其应用前景与发展潜力进行了展望,提出海水抽水蓄能系统与可再生能源的耦合将是其近期主要的发展方向。     

新型蓄能空调系统全年电力负荷转移率研究

以采用溴化锂溶液的新型蓄能空调系统为研究对象,采用数值模拟的方法对蓄能空调系统在分量蓄能策略下整个空调季节的工作情况进行模拟,得出蓄能空调系统在整个空调季节内电力负荷转移率的大小以及蓄能空调系统工作性能及参数的变化规律.     

Approximate analytical model for PCM solidification in a rectangular finned container with convective cooling boundaries

Thermal energy storage units that utilize latent heat storage materials have received increased attention in the recent years because of their relatively large heat storage capacities and isothermal behavior during charging and discharging. In this study, an analytical approach is presented for the prediction of temperature during the solidification in a two-dimensional rectangular latent heat storage using a phase change material (PCM) with internal plate fins. The basic energy equation is formulated accounting for the presence of a heat thermal fluid (HTF) on the walls. A two-dimensional numerical model is developed based on the enthalpy method to predict the distribution temperature of the fin and solid–liquid interface in storage. Results from the analytical solution and numerical model show a good agreement. The developed analytical model estimates satisfactorily the solidification time of PCM in storage, which is useful in the design of PCM-based thermal energy storages and cooling systems.     

Role of metal foam in solidification performance for a latent heat storage unit

The current latent heat storage (LHS) units are usually poor in energy charging and discharging efficiency. Given this, a two dimensional (2D) numerical model of the energy discharging process is presented and comprehensively analyzed to predict the role of metal foam in the solidification performance of LHS units. In the model, the fractal geometry reconstructed by the fractal Brownian motion is utilized for the pore characterization of the metal foam. The proposed model is validated through a melting experiment in copper foams from the reference. The temperature dynamic response and the solidification front evolution in metal foam are analyzed and compared to those in a corresponding cavity. The roles of the fractal dimension and porosity in the solidification behaviors are quantitatively analyzed. The results report that the presence of metal foam enhances the solidification performance. For the main goal of maximizing the latent storage, the appropriate porosity of an LHS unit is dependent on the duration time for the heat discharging process in the real application of thermal energy storage. Even if the porosity is the same, the fractal dimension also affects the solidification performance. A decrease in the fractal dimension (lower degree of disorder for pore distribution) provides greater access to heat flow through the phase change material-foam composite and thus leads to improvement in the interstitial heat transfer, which in turn accelerates the rate of heat release. The fractal dimension is expected to be less than 1.5 for superior solidification performance.     

三套管式相变蓄热器强化传热研究

基于三套管式相变蓄热器的特点,提出应用T字形翅片来强化相变蓄热器的传热性能。研究结果表明:添加翅片可有效地降低蓄热器中相变材料的凝固和融化时间,直翅片和T字形翅片的混合强化结构能使凝固过程比未强化结构节省74%的时间,使融化过程节省60%的时间。因此直翅片和T字形翅片的混合使用可以达到进一步强化传热的目的。     

Characterization of metals and salts‐based thermal energy storage materials using energy balance method

Thermal energy storage technologies minimize the imbalance between energy production and demand. In this context, latent heat storage materials are of great importance as they have a higher density of energy storage as compared with the sensible heat storage materials. The present study involves the characterization of energy storage materials using an energy balance cooling curve analysis method. The method estimates the convective heat transfer coefficient in the solidification range to characterize the phase change materials for applications in energy storage. The method is more beneficial than the Computer Aided Cooling Curve analysis methods as it eliminates baseline calculations and the associated fitting errors. Metals (Sn) and salts (KNO₃ and NaNO ₃) were used in the present work. Phase change characteristics like the rate of cooling, liquidus and solidus temperatures, time for solidification, and enthalpy of phase change were estimated for both metals and salts. It was observed that the energy balance cooling curve analysis method worked very well for metals but not well suited for low conductivity salts. Salts could not be characterized since the thermal gradient existing within the salt sample was not considered in this method.     

Energy storage and solidification of paraffin phase change material embedded with graphite nanofibers

Phase change materials (PCMs) are known to be excellent candidates for thermal energy storage in transient applications. However, enhancement of the thermal conductivity of a paraffin-based PCM is required for effective performance, particularly during solidification where diffusion is the dominant heat transfer mode. This study experimentally examines the effect that graphite nanofibers (GNFs), aspect ratio and power density have on both thermal storage and solidification time of a PCM which is embedded between two sets of aluminum fins. Additionally, a figure of merit is introduced in order to quantify the effectiveness of each of these three parameters with respect to solidification time. GNF enhancement was shown to reduce the maximum temperature in the thermal containment unit (TCU) by 48%. It was also found that for aspect ratios of 1, the GNF enhancement shortens solidification time by as much as 61% over the paraffin samples. This research indicates that GNF impregnation into phase change materials is an effective method for the enhancement of the thermal energy storage and the solidification of paraffin-based phase change materials.     

Research on melting and solidification processes for enhanced double tubes with constant wall temperature/wall heat flux

Latent heat thermal energy storage (LHTES) improves the energy utilization efficiency between energy supply and energy demand of heating storage in buildings and liquid desiccant air conditioning systems. The present work is focused on validated numerical investigation of the thermal performances of LHTES inside enhanced double tubes. The effects of the number of fins ranging from 2 to 10 and boundary conditions of the inner tube wall on the melting and solidification processes are examined. The results indicate that number of fins and wall boundary conditions play an important role in the thermal performances of LHTES. It is noted that recirculation flow in the liquid phase change material region is formed remarkably. The enhancement ratio for constant wall temperature is more significant than that of constant wall heat flux during the melting process. However, the discrepancy of the enhancement ratio for different inner wall temperatures is limited during the solidification process.     

Enhancement of latent heat energy storage using embedded heat pipes

Latent heat thermal energy storage (LHTES) utilizing heat pipes or fins is investigated experimentally. Photographic observations, melting and solidification rates, and PCM energy storage quantities are reported. Heat pipe effectiveness is defined and used to quantify the relative performance of heat pipe-assisted and fin-assisted configurations to situations involving neither heat pipes nor fins. For the experimental conditions of this study, inclusion of heat pipes increases PCM melting rates by approximately 60%, while the fins are not as effective. During solidification, the heat pipe-assisted configuration transfers approximately twice the energy between a heat transfer fluid and the PCM, relative to both the fin-assisted LHTES and the non-heat pipe, non-fin configurations.