Temperature-dependent thermal properties of a paraffin phase change material embedded with herringbone style graphite nanofibers
Temperature-dependent thermal properties of a paraffin phase change material embedded with herringbone style graphite nanofibers
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DOI：
10.1016/j.apenergy.2014.03.091
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发表时间：
2015
期刊：
影响因子：
11.2
通讯作者：
R. Warzoha;R. Weigand;A. Fleischer
中科院分区：
文献类型：
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作者：
R. Warzoha;R. Weigand;A. Fleischer
在许多研究中，具有高导热系数（10-3000 W/m K）的碳纳米颗粒已被嵌入相变储能材料（PCMs）中，以提高其整体热性能。迄今为止，大量的工作都集中在确定这些纳米颗粒对PCM固相热性能的影响上，但对它们对其液相热性能的影响知之甚少。因此，本研究定量了植入随机定向的人字形石墨纳米纤维（HGNF，平均直径= 100 nm，平均长度= 20 μm）对有机石蜡PCM （IGI 1230A,Tmelt= 329.15 K）固液相体热性能的影响。得到了HGNF/PCM纳米复合材料的体积导热系数、体积热容和热扩散系数随温度和HGNF体积载荷水平的变化规律。结果表明，材料相的不同，其性能增强有显著差异。为了解释固液相热性能的差异，研究了纳米颗粒- pcm和纳米颗粒-纳米颗粒界面的热流作为HGNF加载水平和温度的函数。为了做到这一点，纳米颗粒与周围PCM之间和/或接触纳米颗粒之间的固相和液相热边界电阻（TBRs）被发现。结果表明，在固相和液相中，HGNF-PCM界面处的TBR几乎是HGNF-HGNF界面处TBR的两倍。然而，当PCM处于固相时，HGNF-PCM和HGNF-HGNF TBRs比PCM处于液相时至少低一个数量级。最后，为了确定HGNF/PCM纳米复合材料在各种能源体系中的适用性，研究了纳米纤维浓度对PCM熔合潜热和熔体温度的影响。
In many studies, carbon nanoparticles with high values of thermal conductivity (10–3000 W/m K) have been embedded into phase change thermal energy storage materials (PCMs) in order to enhance their bulk thermal properties. While a great deal of work to date has focused on determining the effect of these nanoparticles on a PCM’s solid phase thermal properties, little is known about their effect on its liquid phase thermal properties. Thus, in this study, the effect of implanting randomly oriented herringbone style graphite nanofibers (HGNF, average diameter = 100 nm, average length = 20 μm) on the bulk thermal properties of an organic paraffin PCM (IGI 1230A,Tmelt= 329.15 K) in both the solid and liquid phase is quantified. The bulk thermal conductivity, volumetric heat capacity and thermal diffusivity of HGNF/PCM nanocomposites are obtained as a function of temperature and HGNF volume loading level. It is found that the property enhancement varies significantly depending on the material phase. In order to explain the difference between solid and liquid phase thermal properties, heat flow at the nanoparticle–PCM and nanoparticle–nanoparticle interfaces is examined as a function of HGNF loading level and temperature. To do this, the solid and liquid phase thermal boundary resistances (TBRs) between the nanoparticles and the surrounding PCM and/or between contacting nanoparticles are found. Results suggest that the TBR at the HGNF–PCM interface is nearly double the TBR across the HGNF–HGNF interface in both solid and liquid phases. However, both the HGNF–PCM and HGNF–HGNF TBRs are at least an order of magnitude lower when the PCM is in its solid phase versus when the PCM is in its liquid phase. Finally, the effect of nanofiber concentration on the PCM’s latent heat of fusion and melt temperature is investigated in order to determine the applicability of the HGNF/PCM nanocomposite in a wide variety of energy systems.