TPS法测定泡沫铜/石蜡复合相变材料热物性

运用瞬态平面热源法(Transient Plane Source-TPS)对4种孔隙率的泡沫铜/石蜡复合材料热物性进行了测量。以10μm厚的镍金属按双螺旋线布置作为测量探头。泡沫铜材料孔隙率分别为ε=97.79%、ε=96.17%、ε=94.94%和ε=93.26%,经线切割加工后向内灌入液态石蜡,凝固后作为测试样品。在室温(25±1℃)和常压下对复合材料的等效导热系数、热容及热扩散率进行了测量。测试结果表明:复合材料导热系数和热扩散率因泡沫铜的加入而大幅提高,在孔隙率ε=93.26%时,等效导热系数已达到单纯石蜡的25倍,而复合材料等效热容则由于铜金属加入的绝对量较少相对原石蜡热容变化较小。以比例加成的方法对泡沫铜/石蜡复合材料的等效热容进行了计算,并利用实验数据拟合了其等效导热系数的计算公式,运用这些公式对复合材料物性的计算结果与实验结果非常吻合。     

石蜡基碳纳米管复合相变材料的热物性研究

以多壁碳纳米管为填料,制备了不同质量分数(1%～5%)的石蜡基纳米复合相变材料。采用差示扫描量热技术对所制备复合相变材料的相变特性进行了表征,其导热性能则通过瞬态热线法导热仪进行了测量。实验结果发现,虽然复合相变材料的相变温度几乎不变,但其相变焓则随碳纳米管的加载量的增加而近似线性下降。在质量分数为5%时,相变焓较纯石蜡下降了约15%。复合相变材料的导热系数大致随温度的升高而降低,而在30和50℃时分别由于固固和固液相变的作用,导热系数测量值出现了较大程度的突增。此外,导热系数随质量分数呈线性增长的趋势,在质量分数为5%时,最大的相对提升率接近40%,展现了良好的导热强化效果。     

石蜡/膨胀石墨复合相变储热材料的研究

以膨胀石墨为基体,石蜡为相变储热介质,利用膨胀石墨对石蜡良好的吸附性能,制备出了石蜡／膨胀 石墨复合相变储热材料。由于毛细作用力和表面张力的作用,石蜡在固-液相变时,很难从膨胀石墨的微孔中渗 透出来。实验结果表明,石蜡/膨胀石墨复合相变储热材料没有改变膨胀石墨的结构和石蜡的固-液相变温度, 且其结合了石墨高的导热系数和石蜡大的相变潜热,因而储热密度较高,导热性能好。其相变潜热与对应质量 分率下的石蜡相当,储/放热时间比石蜡明显减少。     

二元有机复合相变材料相变过程热特性实验研究

二元有机复合相变材料因其无腐蚀性、过冷度低、价格低廉和可循环性的优点,在电子器件散热过程中极具发展潜力。通过差示扫描量热法(DSC)测得 4 种脂肪酸和 4 种脂肪醇相变温度与潜热,然后利用准共晶相变理论计算脂肪酸/醇二元有机复合相变材料共晶点,确定 4 种相变温度在 33～37 ℃ 范围内的复合体系,并通过 DSC 实验测量二元体系相变特性。实验结果表明,筛选出的二元有机复合相变材料相变温度分布在 33.08～36.63 ℃,与理论相变温度偏差在0.30%～4.61%;相变潜热分布在 138.5～215 kJ·kg^-1,与理论相变潜热偏差在 0.4%～27%;十二酸与十八醇复合相变材料具有最高的相变潜热(215 kJ·kg^-1),相变温度为 36.5 ℃。研究结果可为有机复合相变材料在电子器件热管理中的应用提供技术参考。     

热适应复合相变材料的制备与热性能

根据电子器件散热技术领域对热适应复合材料的性能要求,选取导热系数高且密度低的膨胀石墨作为无机支撑材料,石蜡作为有机相变材料,制备出高导热系数和储热密度的热适应复合相变材料.采用扫描电镜(SEM)、差示扫描量热仪(DSC)、偏光显微镜(POM)和Hot Disk热常数分析仪等多种测试技术,对复合相变材料进行分析研究;通过储/放热实验和1000次热循环实验研究了复合相变材料的传热性能和热稳定性.实验结果说明该复合相变材料具有形状稳定、导热率高、储热密度大等特点,并具有良好的热稳定性和使用寿命.     

石墨-石蜡复合相变材料的圆柱型动力电池组热管理性能

本工作以21700容量型NCM811锂离子动力电池为研究对象,设计了正六边形布置的电池模组,外覆圆柱型石墨-石蜡复合相变材料的结构.利用数值模拟方法探究了不同恒定倍率放电,以及相邻两电池不同间距对模组热特性的影响.结果表明,对于不同倍率,相邻电池间距对电池模组高倍率放电过程中的温度影响要远大于低倍率放电过程,而对于相同倍率,小间距模组从放电开始至结束的温升要高于中间距和大间距模组.电池温度的变化相对于热流量在时间上有一定滞后,通过监测热流量的数值,能够对电池热管理的失效做出提前预知,提高电池组的安全性.     

新型相变贮热材料

在太阳能热利用、工业余热回收、采暖及空调领域中 ,为了调整热能供应与人们需求之间的不一致 ,热能的贮存是极为关键的一环。目前普遍使用的贮热方式有两大类 :显热式贮热和潜热式贮热。所谓显热式贮热 ,就是通过加热介质 ,使其温度升高而贮热 ,它也叫“热容式贮热”。潜热式贮热是利用贮热介质被加热到相变温度时吸收大量相变热而贮热 ,它也叫“相变式”贮热。物质由固态转变为液态（熔解） ,由液态转变为气态（气化） ,或由固态直接转变为气态（升华） ,都会吸收相变热 ;而进行逆过程时则释放相变热。这是潜热式贮热所依据的基本原理 ,在…     

相变贮热材料的DSC研究

用ＤＳＣ法研究了多元醇，层状钙钛矿等几种相变材料的热物理性能，它们都是有希望的贮热材料，实验所得数据是评价和选择这些材料的主要依据。     

金属蜂窝/石蜡复合相变材料融化储热性能研究

针对金属蜂窝/石蜡复合相变材料融化储热过程中,金属蜂窝热传导与液相自然对流传热的竞争关系,基于流-固-热三场耦合理论,建立相变材料融化储热计算模型。开展相变石蜡融化试验,验证计算模型的正确性。进一步分析液相自然对流和金属蜂窝热传导传热的增强效应,以及两者间的竞争关系。结果表明：底部加热下的密闭方腔内相变石蜡融化储热过程可分为热传导、稳定增长、过渡和紊流等四个阶段;各阶段占总融化储热时间的比例分别为0.8%、2.3%、13.6%和83.3%。热量随着液相石蜡的自然流动实现无障碍传输,达到提升相变石蜡融化储热效率的目的。自然对流传热的增强效应随尺寸减小而显著降低,在尺寸小于2 mm后可忽略不计。金属蜂窝通过增大热传导性和传热面积,达到提升相变石蜡融化储热效率的目的。嵌入金属蜂窝后,相变材料储热过程中存在多层共融现象,且在融化区形成温度梯度。与纯石蜡储热效率相比,金属蜂窝作用呈现先增强后抑制的规律,当融化分数超出临界值0.77后,金属蜂窝将进入抑制阶段。     

Structure and thermal properties of expanded graphite/paraffin composite phase change material

Different contents of expanded graphite (EG) composite phase change material (PCM) were prepared by the melt mixing method, taking paraffin as the PCM and EG as the supporting material. Phase compositions of EG, paraffin, and EG/paraffin composite were investigated using X-ray diffraction (XRD). Microstructures of EG and EG/paraffin composite PCMs with different EG contents were observed by a scanning electron microscope (SEM). Thermal properties, such as phase-transition temperature and latent heat of the materials, were determined by differential scanning calorimetry (DSC). Mass loss and thermal properties after 100 heating cycles were measured. The results show that physical absorption exists between paraffin and EG. EG is beneficial for the PCM composite to reduce leakage of paraffin, decrease the phase change temperature and latent heat, and strengthen the thermal stability. The solid–liquid phase change latent heat of materials is larger than that of the solid–solid one. The heating cycle has little effect on the phase-transition temperature and latent heat.     

Preparation and thermal energy properties of paraffin/halloysite nanotube composite as form-stable phase change material

Phase change materials (PCMs) have attracted extensively interests in solar storage. In the study, we prepared a new kind of composite PCM by impregnating paraffin (P) into halloysite nanotube. The as-prepared composite PCM was characterized by TEM, FT-IR and DSC analysis techniques. The composite can absorb paraffin as high as 65 wt.% and maintain its original shape perfectly without any paraffin leakage after subjected to 50 melt–freeze cycles. The melting temperature and latent heat of composite (P/HNT: 65/35 wt.%) were determined as 57.16 °C and 106.54 J/g by DSC. Graphite was added into the P/HNT composite to improve thermal storage performance, and the melting time and freezing time of the composite were reduced by 60.78% and 71.52% compared with the composite without graphite, respectively. Due to its high adsorption capacity, high heat storage capacity, good thermal stability and simple preparation method, the composite can be considered as cost-effective latent heat storage material for practical application.     

Micro-encapsulated paraffin/high-density polyethylene/wood flour composite as form-stable phase change material for thermal energy storage

Six novel polymer-based form-stable composite phase change materials (PCMs), which comprise micro-encapsulated paraffin (MEP) as latent heat storage medium and high-density polyethylene (HDPE)/wood flour compound as supporting material, were prepared by blending and compression molding method for potential latent heat thermal energy storage (LHTES) applications. Micro-mist graphite (MMG) was added to improve thermal conductivities. The scanning electron microscope (SEM) images revealed that the form-stable PCMs have homogeneous constitution and most of MEP particles in them were undamaged. Both the shell of MEP and the matrix prevent molten paraffin from leakage. Therefore, the composite PCMs are described as form-stable PCMs. The differential scanning calorimeter (DSC) results showed that the melting and freezing temperatures as well as latent heats of the prepared form-stable PCMs are suitable for potential LHTES applications. Thermal cycling test indicated the form-stable PCMs have good thermal stability although it was subjected to 100 melt–freeze cycles. The thermal conductivity of the form-stable PCM was increased by 17.7% by adding 8.8 wt% MMG. The results of mechanical property test indicated that the addition of MMG has no negative influence on the mechanical properties of form-stable composite PCMs. Taking one with another, these novel form-stable PCMs have the potential for LHTES applications in terms of their proper phase change temperatures, improved thermal conductivities, outstanding leak tightness of molten paraffin and good mechanical properties.     

Analysis of electrical resistivity of expanded graphite/paraffin composite phase change material

采用熔融共混法制备石蜡/膨胀石墨复合相变材料,使用半导体粉末电阻率测试仪对天然鳞片石墨、提纯石墨、可膨胀石墨、石蜡/膨胀石墨复合相变材料在不同压强下的电阻率进行测试。发现所有材料的电阻率都随压强的增加而减小,对导热性能最好的相变材料进行7次重复测试,材料电阻率在0.210～0.535 Ω·cm之间变化,依然小于1 Ω·cm,属于低电阻率材料。根据测试数据计算不同压强情况下相变材料单位体积蓄热量、密度、体积和电阻值。材料的单位体积蓄热量和密度随压强增大而增大,体积和电阻则相反,压强在4～10 MPa之间时物理性能比较稳定,在10 MPa左右时,相变材料电阻值比天然鳞片石墨最大增大884倍、体积1.9倍、密度0.6倍,单位体积蓄热量同比4 MPa时最大增加22.8%,压缩之后单位体积蓄热量提高。说明膨胀石墨/石蜡复合材料属于低电阻率相变材料,应用于沥青路面,能够实现升温和降温的双重效果。     

Thermal conductivity and latent heat thermal energy storage characteristics of paraffin/expanded graphite composite as phase change material

This study aimed determination of proper amount of paraffin (n-docosane) absorbed into expanded graphite (EG) to obtain form-stable composite as phase change material (PCM), examination of the influence of EG addition on the thermal conductivity using transient hot-wire method and investigation of latent heat thermal energy storage (LHTES) characteristics of paraffin such as melting time, melting temperature and latent heat capacity using differential scanning calorimetry (DSC) technique. The paraffin/EG composites with the mass fraction of 2%, 4%, 7%, and 10% EG were prepared by absorbing liquid paraffin into the EG. The composite PCM with mass fraction of 10% EG was considered as form-stable allowing no leakage of melted paraffin during the solid–liquid phase change due to capillary and surface tension forces of EG. Thermal conductivity of the pure paraffin and the composite PCMs including 2, 4, 7 and 10 wt% EG were measured as 0.22, 0.40, 0.52, 0.68 and 0.82 W/m K, respectively. Melting time test showed that the increasing thermal conductivity of paraffin noticeably decreased its melting time. Furthermore, DSC analysis indicated that changes in the melting temperatures of the composite PCMs were not considerable, and their latent heat capacities were approximately equivalent to the values calculated based on the mass ratios of the paraffin in the composites. It was concluded that the composite PCM with the mass fraction of 10% EG was the most promising one for LHTES applications due to its form-stable property, direct usability without a need of extra storage container, high thermal conductivity, good melting temperature and satisfying latent heat storage capacity.     

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、太阳能发电等领域应用广泛,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.采用三周期性极小曲面(triply periodic minimal surface,TPMS)生成泡沫铝骨架,基于孔隙尺度数...     

石蜡/泡沫铝复合相变材料对太阳池热性能的影响

传统盐梯度太阳池以显热储热,储热密度较低。提出了在储热层添加石蜡/泡沫铝复合多孔介质相变层的方法,构建了宽度为300mm,长度为400mm,深度为500mm的小型实验太阳池,分别进行了传统盐梯度太阳池和添加石蜡/泡沫铝复合多孔介质相变材料(PCM)的太阳池热性能对比实验。实验研究与理论分析表明:未添加石蜡/泡沫铝复合PCM的下对流层(LCZ)的储存(火用)和(火用)效率的最大值分别13.814 MJ/m³与9.38%;添加4块石蜡/泡沫铝复合PCM的LCZ的储存(火用)和(火用)效率的最大值分别为15.659 MJ/m³与12.05%,同前者对比分别提高了1.845 MJ/m³与2.67%,从而证明石蜡/泡沫铝复合PCM能够有效提高LCZ的储存(火用)与(火用)效率。此外,后者在太阳池LCZ的温度上升期可使其温度提高3℃左右,因此,添加石蜡/泡沫铝复合PCM能够提升太阳池LCZ的蓄热能力。     

Thermal properties of paraffin/graphite composite phase change materials in battery thermal management system

Abstract

The thermal properties of paraffin/graphite composite phase change materials for power nickel metal hydride batteries were experimentally investigated. Two different modes for heat dissipation were designed in this experimental study: air cooling and cooling with phase change materials. Paraffin/graphite composite phase change thermal energy storage materials were prepared and tested by differential scanning calorimetry. It appeared that the battery thermal management system with phase change materials had better performance than air cooling, especially when the scale of paraffin/graphite composite material approximates 4:1.     

RETRACTED: Preparation and thermal properties of form-stable paraffin phase change material encapsulation

Form-stable paraffin phase change materials (PCMs), in which the paraffin as a latent heat storage material and the polyolefins as a supporting material, have to be encapsulated because of the paraffin leakage and lipophilicity. A novel microencapsulated PCM in which form-stable paraffin is encapsulated into inorganic silica gel polymer is prepared successfully by in situ polymerization. A differential scanning calorimeter (DSC) is used to measure the thermal properties of the PCM. Moreover, the Washburn equation associated with the wetting properties of powder materials, is used to test the hydrophilic–lipophilic properties of PCM. The results indicate that the optimum microencapsulated PCM is endowed with good hydrophilicity, and its specific enthalpy maintains 123.78 J g⁻¹.     

三水合乙酸钠/蛭石复合相变蓄热材料性能优化研究

采用真空浸渍法将三水合乙酸钠（sodium acetate trihydrate,SAT）吸附在膨胀蛭石（expanded vermiculite,EV）微孔内,选择EV吸附SAT能力最佳的质量比为1:6。通过扫描电子显微镜（scanning electron microscopy,SEM）观察复合相变材料（composite phase change material,CPCM）的微观结构,显示EV微孔几乎完全被SAT填充。X射线衍射（X-ray diffraction,XRD）表明SAT与EV化学相容性较好,二者仅发生物理相互作用。通过差式扫描量热法（differential scanning calorimetry,DSC）测试EV在最大吸附能力下,复合材料的相变温度为57.6℃,接近SAT理论相变温度58.1℃;相变潜热为238.8kJ/kg。热重分析（thermogravimetric analysis,TG）结果显示复合材料热稳定性良好。因为EV负载体将SAT间隔为无数微单元,有效改善SAT相变过程中过冷和相分离现象,起到成核剂和悬浮剂的作用。实验研究结果表明,制备的CPCM具有较好的热物性以及稳定的热循环性能,有望成为相变蓄热材料应用于冬季供暖。