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。     

泡沫铜对相变蓄热系统蓄热性能影响的实验研究

石蜡作为一种有机固液相变材料,因其具有高潜热值、无毒、无腐蚀、性能稳定等优点被广泛应用于热蓄存、电子冷却及建筑温控等领域。但在蓄热过程中,因石蜡导热系数较低,导致蓄热时间过长、温差过大。实验按照1∶3的比例将泡沫金属铜均匀分布在石蜡箱体中,探究泡沫铜对石蜡相变速率的影响。结果显示:加入泡沫铜后,有效地提升了石蜡的相变速率,缩短了石蜡相变的时间;同时加入泡沫铜后,石蜡内部温差明显减小,温度分布更加均匀,并且有效缓解了自然对流造成的顶部过热和底部不熔化现象。     

基于泡沫铜/石蜡的动力电池散热性能研究

石蜡作为一种相变材料具有稳定性好、成本低廉等优点,但是其缺点是导热系数较低。利用泡沫铜的多孔结构,将石蜡压入泡沫铜的孔隙中作为相变材料的本体,在此结构中,泡沫铜不仅发挥了多孔连续框架的优势,而且作为强化传热骨架,结合了石蜡相变吸热的性质,在一定程度上弥补了石蜡导热系数较低的不足。实验对电池和电池模块进行不同工况、不同放电倍率的测试,比较各工况下单体电池及电池模块温度分布情况,可以得出泡沫铜/石蜡相变材料冷却系统中动力电池的散热效果非常明显。     

泡沫金属内石蜡相变凝固的数值模拟

研究了泡沫金属中相变材料的相变熔化过程,由于金属骨架和相变材料传热性能的巨大差异,建立了骨架和相变材料的双温度模型,采用显热容法进行了数值模拟。模拟结果显示,相变材料中填充泡沫金属,能有效改善相变材料的温度分布;在相变时,骨架与相变材料的温差较大,局部热不平衡明显;泡沫金属孔隙率越小,石蜡熔化越快。     

Solidification process analysis of a heat storage device containing graphite foam and paraffin

石蜡相变材料的导热系数较小,严重影响了其传热速率和凝固速率。通过对填充石墨泡沫/石蜡的储能系统进行凝固过程的模拟,确定了石墨泡沫对相变储能系统性能的影响。研究结果表明石墨泡沫不仅大大缩短了相变凝固时间,也使储能系统的温度分布更加均匀;通过分析冷却水进口速度和温度对复合相变材料的凝固过程的影响,说明随着冷却水进口速度的增大和温度的降低,传热速率加快,凝固时间缩短。分析了复合材料相变区的自然对流对相变过程的影响,模拟结果证明自然对流能在一定程度上加快相变材料的凝固过程。     

铝/石蜡复合相变材料蓄热性能的数值模拟

相变储能材料由于其具有周期性储存和释放能量的特点,在电池热管理、太阳能发电等领域存在着广泛的应用。然而由于导热系数低的原因限制了其进一步的应用。高导热率泡沫材料的添加为解决这一不足提供了一种有效的方法。文章采用三周期性极小曲面（TPMS）生成泡沫铝骨架,基于孔隙尺度数值模拟了铝/石蜡复合相变材料相变蓄热的变化规律。结果表明：铝骨架的添加强化了蓄热,缩短了融化时间,在复合相变材料孔隙率为0.90、0.85、0.80时,相比于纯石蜡,完全融化时复合相变材料的融化时长分别缩短了68％、75％和80％,而且蓄热过程中温度场更加均匀;验证了铝骨架与石蜡之间由于热导率存在较大的差异,存在的热非平衡效应,且铝/石蜡复合相变材料孔隙率越低,此效应越明显     

基于场协同原理的异型管强化石蜡蓄放热性能分析

将1.5%石墨烯/石蜡复合相变材料填充到内管形状不同、换热面积相同的套管换热器内,采用数值模拟的方法分析内管形状对石蜡类复合相变材料蓄放热性能的影响。结果表明,异型管能有效提升石蜡复合相变材料的熔化及凝固速率,滴型管外石蜡复合相变材料的熔化速率比椭圆管及圆管分别提高53%、62%,滴型管外石蜡复合相变材料的凝固速率比椭圆管及圆管分别提高6.7%、9.8%。基于场协同原理分析异型管的强化石蜡类复合相变材料的传热机理,由于滴型管能使石蜡类复合相变材料在相变过程中温度场与速度场协同性更高,因此能更有效地提升其相变速率。     

格子Boltzmann方法模拟泡沫金属内相变材料热传导融化传热过程

基于局部热非平衡条件下泡沫金属内热传导融化相变传热的非线性双温度方程,在表征单元尺度上构建双温度分布函数格子Boltzmann模型,其中相变非线性源项处理采用焓法迭代求解。数值模拟了金属骨架与相变材料的温度分布情况,重点分析了孔径、金属骨架与填充材料热传导比和Stefan数等对局部热非平衡效应的影响。模拟结果表明,孔径越大、金属骨架与填充材料热传导比越大,局部热非平衡效应越明显;相变过程的存在,加大了局部热非平衡效应,并且Stefan数越低局部热非平衡效应则越大。     

金属泡沫内石蜡固液相变蓄热/放热实验

针对解决太阳能热利用过程中所面临的辐射强度不稳定、不连续和不均匀等关键问题,相变蓄热技术常与太阳能热利用系统耦合协同匹配,以实现稳定连续的热量输出.为了强化固液相变蓄热/放热过程、提高系统热储能效率,对金属泡沫内石蜡类相变材料(PCMs)在不同蓄热流体温度下的固液相变蓄热/放热特性开展了实验研究.设计并搭建了相界面可视...     

泡沫金属-PCM-液冷复合方式下动力电池散热分析

电池是电动汽车的核心动力元件,而电池的热管理系统是动力电池发挥最佳工作性能的重要保障,在保证最佳工作性能的同时提升汽车安全性能、电池寿命及能源利用效率。基于21700NCA圆柱型三元锂离子电池,建立以泡沫铝为支撑骨架的电池组系统,在骨架和电池之间的孔隙注入相变材料（PCM）以提高结构内部温度均匀性,在电池底部添加液冷板来强化冷却效果,利用计算流体力学（CFD）仿真技术分析单体电池的耦合散热效果。结果表明,与单一冷却模式相比,使用泡沫金属与相变材料、液体冷却的耦合散热系统,可以达到更加良好的散热效果;对于相变材料,在一定密度范围内,密度越大,对电池系统的冷却效果越好,混合比主要影响相变材料的凝固融化速率。     

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.     

Numerical model of the passive thermal management system for high-power lithium ion battery by using porous metal foam saturated with phase change material

A two-dimensional transient model for a passive thermal management system was developed for commercial square lithium ion battery by using the phase change material (PCM) of paraffin saturated in metallic copper foam. This model combined the thermo-electrochemical model for the battery and a model that characterized the solid–liquid phase change of paraffin in copper foam. The thermo-electrochemical model was composed of species conservation, charge conservation, and energy balance equations. In the model of phase change in metal foam, the non-Darcy, natural convection of melted paraffin, and local thermal non-equilibrium effects were considered. The thermo-electrochemical performance of the battery and convective heat transfer behavior of the foam-PCM composite were investigated. The predicted results were in agreement with experimental data. Compared to the air convection and adiabatic modes, the thermal management by foam-PCM composite has dramatically reduced battery surface temperature to the allowable range at 1C and 3C discharge rates.     

Passive thermal management using metal foam saturated with phase change material in a heat sink

An electronic passive thermal management system was designed. The system featured a hybrid heat sink with parallel fins sintered onto its top and copper metal foam–paraffin composite saturated in its hollow basement. The other two types of basement patterns for thermal dissipation were also employed: (1) a hollow basement saturated with pure paraffin; (2) a solid copper basement. The experimental results showed that the use of the copper metal foam reduced the surface temperature and the time required to reach the melting point of the paraffin. Lower surface temperature can be achieved by either reducing foam porosity or foam pore density. During the melting process, temperature increased more linearly for the foam–PCM composite than for the case of pure paraffin since the enhancement in thermal conduction caused by the metal foam exceeded the level of its suppression to natural convection of melted paraffin.     

Thermal energy storage properties of the capric acid–stearic acid binary system and 48# paraffin–liquid paraffin binary system

In this paper, the phase change temperature, latent heat and thermal stability of the capric acid–stearic acid binary system and 48# paraffin–liquid paraffin binary system were experimentally studied. The experimental results showed that the phase change temperature and phase change latent heat change with the content of the component. The phase change temperature of binary mixtures changes in a wide range, so they can be used in different fields by adjusting mixing ratio. The phase change latent heat of fatty acid mixtures is higher than that of paraffin mixtures. The thermal stability of fatty acid mixtures is better than that of paraffin mixtures. The mixtures used in the phase change material (PCM) wall or the PCM floor as energy storage materials are given in the paper.     

Thermal energy storage properties of a capric acid/stearic acid binary system and a 48# paraffin/liquid paraffin binary system

In this paper, the phase change temperature, latent heat and thermal stability of a capric acid/stearic acid binary system and a 48# paraffin/liquid paraffin binary system were experimentally studied. The experimental results showed that the phase change temperature and phase change latent heat change with the content of the component. The phase change temperatures of binary mixtures change in a wide range, so they can be used in different fields by adjusting the mixing ratio. The phase change latent heat of fatty acid mixtures is higher than that of paraffin mixtures. The thermal stability of fatty acid mixtures is better than that of paraffin mixtures. The mixtures used in the phase change material wall or the phase change material floor as energy storage materials were given in the paper.