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《工程热物理学报》2015,(6)
本文以十二烷为相变材料,利用膨胀石墨多孔吸附特性制备出十二烷/膨胀石墨复合相变蓄冷材料。通过扫描电镜(SEM)、差示扫描量热仪(DSC)和热常数分析仪(HotDisk)对复合相变材料的结构及热性能进行了表征。实验结果表明,十二烷被膨胀石墨均匀吸附,吸附后膨胀石墨保持了原来的疏松多孔的蠕虫状形态。复合相变材料的相变焓值随着添加的膨胀石墨质量分数增加而降低,导热系数随着添加的膨胀石墨质量分数增加而增加。相变材料质量分数为80%,复合相变材料熔化焓和凝固焓分别为132.8 J/g和132.5 J/g,表观密度为700 kg/m~3时,导热系数为2.64 W/(m·K)。复合相变材料具有良好的热循环稳定性能。 相似文献
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相变材料利用其相变潜热能力可吸收储存和释放利用热量,同时在相变过程中其温度浮动小,能够实现温度控制从而用于热管理.但是其低热导率和易泄露问题严重制约了其性能.石墨烯气凝胶因其丰富的多孔结构而具有较大的比表面积,可吸附相变材料解决其泄露问题,同时石墨烯的高导热系数可提高相变材料的热导率.这里选取正十八烷为相变材料,制备了不同质量分数的石墨烯气凝胶复合相变材料.测得石墨烯气凝胶含量为13.99 wt%的样品,其导热系数比纯正十八烷高出306.2%,熔化潜热和凝固潜热分别下降了13.8%和10.8%.分子动力学模拟结果表明,石墨烯气凝胶的引入会在一定程度上增强正十八烷分子的有序性和一致性,即在同一温度下复合相变材料中的正十八烷分子比纯正十八烷分子拥有更集中分布的末端距和扭转角,径向分布函数和自扩散系数都相对较低,说明石墨烯材料的引入可以提升正十八烷的导热系数. 相似文献
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针对锂离子电池热失控传播问题,以石蜡/膨胀石墨复合相变材料为电池模组热管理介质,建立电池热失控传播二维数值计算模型。通过改变膨胀石墨与石蜡的质量分数得到不同导热系数与相变焓的复合材料,探究关键设计参数对电池热失控传播的阻断特性。研究结果表明相变材料能够有效延缓甚至阻断热失控的传播,当导热系数较低或较高(如0.3和21.01 W·m-1·K-1)时皆能阻断热失控传播,对于中间导热系数材料的模组,首次热失控传播时间间隔随导热系数升高而增加,而后续传播间隔随着导热系数升高而减小。 相似文献
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基于半经验的Gupta原子间多体相互作用势, 采用分子动力学方法并结合模拟退火及淬火技术, 系统研究了小尺寸铝团簇Aln (n=13–32)的熔化行为. 模拟结果表明: 除个别尺寸(Al13 和Al19) 外, 团簇熔化过程比热曲线普遍呈现杂乱无规(无明显单峰)现象, 这与实验观测小Al团簇比热普遍无规的结果完全一致. 通过分析不同温度点上团簇淬火构型的势能分布图给出了小Al团簇比热呈现无规或有规现象的成因. 对于比热无规团簇, 可以利用原子等价指数判断给出团簇熔点, 所得团簇熔点随团簇尺寸的变化趋势与实验观测结果完全一致.
关键词:
Gupta势
团簇
分子动力学
熔化 相似文献
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采用固相反应法合成了一种Zr Cu Si As型准二维层状锰基化合物Th Mn Sb N.基于X射线粉末衍射的结构精修显示,该化合物属于P4/nmm空间群.其晶胞参数为a=4.1731?, c=9.5160?.电输运测量显示,该化合物电阻率随温度下降缓慢上升,且在16 K附近出现电阻率异常.与此同时,该材料的磁化率在同一温度附近出现异常,显示出类似磁性相变的行为.进一步的比热测量中没有观察到磁相变导致的比热异常.另外,低温下的比热分析显示,该材料的电子比热系数为γ=19.7 m J·mol–1·K–2,远高于其他同类锰基化合物.该结果与电输运测量中观察到的低电阻率行为相符,暗示Th Mn Sb N中费米面附近存在可观的电子态密度.基于对一系列Zr Cu Si As型化合物晶体结构细节的比较,分析了含有萤石型Th2N2层的系列化合物中导电层所受化学压力的不同作用形式. 相似文献
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Xiaowei Sun Qifeng Chen Yandong Chu Chengwei Wang 《Physica B: Condensed Matter》2005,370(1-4):186-194
Shell-model molecular dynamics (MD) simulation has been performed to investigate the melting of the major Earth-forming mineral: periclase (MgO), at elevated temperatures and high pressures, based on the thermal instability analysis. The interatomic potential is taken to be the sum of pair-wise additive Coulomb, van der Waals attraction, and repulsive interactions. The MD simulation with selected Lewis–Catlow (LC) potential parameters is found to be very successful in describing the melting behavior for MgO, by taking account of the overheating of a crystalline solid at ambient pressure. The thermodynamic melting curve is estimated on the basis of the thermal instability MD simulations and compared with the available experimental data and other theoretical results in the pressure ranges 0–150 GPa. Our simulated melting curve of MgO is consistent with results obtained from Lindemann melting equation and two-phase simulated data at constant pressure by Belonoshko and Dubrovinsky, in the pressure below 20 GPa. The extrapolated melting temperatures in the lower mantle are in good agreement with the results obtained from Wang's empirical model up to 100 GPa. Compared with experimental measurements, our results are substantially higher than that determined by Zerr and Boehler, and the discrepancy between DAC and MD melting temperatures may be well explained with different melting mechanisms. Meanwhile, the radial distribution functions (RDFs) of Mg–Mg, O–Mg, and O–O ion pairs near the melting temperature have been investigated. 相似文献
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Using the Stillinger--Weber (SW) potential model, we investigate the
thermal stability of pristine silicon nanowires based on classical
molecular dynamics (MD) simulations. We explore the structural
evolutions and the Lindemann indices of silicon nanowires at
different temperatures in order to unveil atomic-level melting
behaviour of silicon nanowires. The simulation results show that
silicon nanowires with surface reconstructions have higher thermal
stability than those without surface reconstructions, and that
silicon nanowires with perpendicular dimmer rows on the two (100)
surfaces have somewhat higher thermal stability than nanowires with
parallel dimmer rows on the two (100) surfaces. Furthermore, the
melting temperature of silicon nanowires increases as their diameter
increases and reaches a saturation value close to the melting
temperature of bulk silicon. The value of the Lindemann index for
melting silicon nanowires is 0.037. 相似文献
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Solid polymer electrolytes based on high molecular weight poly(ethylene oxide) (PEO) complexed with lithium difluoro(oxalato)borate (LiDFOB) salt in various EO:Li molar ratios from 30:1 to 8:1 were prepared by using solution casting technique. Ion–polymer interaction, structural, thermal, and ionic conductivity studies have been reported by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), polarized optical microscopy (POM), differential scanning calorimeter (DSC), and impedance analysis. FTIR spectral studies suggested that the interaction of Li+ cations with the ether oxygen of PEO, where a triple peak broad band centered at 1105 cm?1, corresponds to C–O–C stretching and extreme deformation occurs. XRD, POM, and DSC indicated that the inclusion of LiDFOB salt could reduce the crystallinity of PEO. The melting temperature of PEO shifted to lower temperature side by the addition of LiDFOB. The glass transition temperature obtained for the system 10:1 was ?38.2 °C. An increase in the ionic conductivity from 3.95?×?10?9 to 3.18?×?10?5 S/cm at room temperature (23 °C) was obtained through the addition of LiDFOB to a high molecular weight PEO. In addition, the ionic conductivity of the polymer electrolyte films followed an Arrhenius relation, and the activation energy decreased with increasing LiDFOB concentration. 相似文献
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分子转动惯量与正烷烃熔沸点的预测 总被引:2,自引:0,他引:2
在分子转动模型基础上,以半经验分子轨道(AM1)方法计算分子的转动惯量及其它结构参数,获得15个正烷烃的沸点和熔点的多元线性回归方程。其中正烷烃的沸点与短轴转动惯量(c)和碳原子数(n)相关(bp=-147.-0.01189c+36.17n,R=0.9985,SD=6.97),而熔点与分子的长轴转动惯量(a)、短轴转动惯量(b,c)及重定向能(E)相关(mp=-260.3+15.70a+19.74 相似文献
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The thermal expansivity and mean-square thermal vibrational amplitudes were determined as a function of temperature for thorium from first principles total energy calculations using the full potential linearized augmented plane wave (FP-LAPW) method. The coefficient of thermal expansion determined from variation of theoretical potential energy with interatomic separation is ~1.427 × 10?5 K?1 as compared to an experimental value of 1.23 × 10?5 K?1. The mean-square thermal vibrational amplitudes determined as a function of temperature from the theoretically calculated volume-dependent Debye temperature agree well with experimental data derived form neutron diffraction measurements. The melting temperature of thorium, determined theoretically from the mean-square thermal vibrations and the Lindemann rule for melting, is 2234 K, as compared to the reported experimental value of 2021 K. 相似文献
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The present research work aimed to investigate the melting and solidification characteristics of NPCM. The NPCM was prepared using paraffin as the PCM and high conductive MWCNT as the nanomaterial without using any dispersant. The NPCM was prepared by dispersing MWCNTs with volume fractions of 0.3%, 0.6% and 0.9% in PCM as the base PCM. SEM morphology showed the uniform dispersion of MWCNTs in the paraffin wax. The MWCNT nano-additives PCMs showed two peaks in the heating curve by DSC measurement. Lessening in melting and solidification time of 30% and 43% was attained in the case of NPCM with 0.3% and 0.9%, respectively. It is observed from the DSC analysis that the latent heat of pure paraffin during freezing and melting cycle was 139.2 J/g (at 56.61 °C) and 131.8 J/g (at 57.55 °C), respectively. Whereas, the latent heat of NPCM with 0.9% of nanofluid was 150.7 J/g (at 56.36 °C) and 148.3 J/g (58.35 °C). It is construed that a maximum change in latent heat of 7.6% and 11% was observed between pure PCM and NPCM during freezing and melting cycle. For the lesser nanoparticle concentration (0.3% and 0.6%), the percentage change in latent heat was lesser than 0.9%. 相似文献
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采用EAM势对6×6×6的Ni-15%Mo合金熔体进行Monte Carlo模拟,通过对不同温度下获得的NVT系统的平衡态统计分析得出Ni-15%Mo合金熔体在过冷态和过热态时的热物理性质.通过构造系统生成新表面,表面张力做功使系统能量发生改变,从而得到液态表面张力的模拟结果.Ni-15%Mo合金熔体的表面张力在1500—2000 K的温度范围内,随温度的变化规律为σ=1.918-1.130×10-3(T-Tm) N/m
关键词:
Monte Carlo模拟
表面张力
比热
Ni-15%Mo合金 相似文献
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L. Benguigui 《Zeitschrift für Physik B Condensed Matter》1966,5(3):171-177
The thermal conductivity of liquid Tellurium was measured by means of a method, the principle of which is recalled. The value of the thermal conductivity is 55·10?3 Wcm?1 deg?1 at the melting point and rises slightly when the temperature increases. These results are explained by admitting the presence of electrons and holes with nearly equal properties. From the values of the electrical and the thermal conductivity a quantitative model is developed. We conclude that liquid Tellurium is a semi-metal. 相似文献
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In this study, a novel phase change material (PCM) of epoxy resin sealed expanded graphite/paraffin composite was developed as an independent attachment for building applications. A relatively high thermal energy storage density and a high thermal conductivity (2.141?W/(m·K)) were obtained in the composite PCM. The mass fraction of paraffin in the composite PCM could reach 94% without leakage of liquid paraffin when being heated at 50°C for more than 3 h, and the thermal cycle stability was good. Moreover, the thermal storage and release properties of this composite PCM with different thicknesses were studied by numerical simulation. The results showed that the thermal storage and release time are proportional to the thickness of the composite PCM, and there was almost no temperature gradient during the thermal storage and release process, which indicated that the thermal conductivity of this kind of composite PCM was high enough for building applications. 相似文献