基于T-history法的相变材料性能分析

相变材料在工程应用前需准确测试其相变潜热与相变点。DSC是最常用的材料热性能表征手段,但DSC设备昂贵,且并不适合块体材料。T-history法设备简单易建,能用于大体积材料测试。该文基于T-history法,通过线性拟合的方法拟合出固相与液相的焓值曲线,并以此确定相变材料的相变点与相变潜热。通过测试癸酸,得到癸酸的相变潜热与相变点分别为166.8J/g和31.9℃。相变潜热与文献报道值相差小于6%,相变点与文献报道值相差小于9%。结果表明此法可用于测试相变材料的相变点与相变潜热。     

304奥氏体不锈钢凝固相转变规律曲线(SPT曲线)建立

利用自行设计的高温凝固相转变测定实验装置,研究了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变过程,得到了凝固过程中液相(L)到高温铁素体(δ)到奥氏体(γ)的相变温度.在此基础上分析了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变规律,从而建立了304奥氏体不锈钢的低冷速凝固相转变规律曲线—SPT(Solidification phase transformation)曲线.结果表明:对试样进行液氮酒精淬火有效地保留了试样高温时各相的状态.可以清楚的显示在不同冷速下的不同温度淬火时液相和固相的各相成份比例及在不同淬火温度下各成份体积比例的变化.通过研究体积比例变化,可以得到304奥氏体不锈钢在不同冷速下的液相线、固相线及各种反应开始和结束的转变温度(即SPT曲线).由SPT曲线也可以看出,随着冷却速度的增大,相转变模式会发生变化,相图会向左移动,各相变反应的温度区间减小.     

奥氏体不锈钢凝固相转变规律曲线(SPT曲线)建立

利用自行设计的高温凝固相转变测定实验装置,研究了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变过程,得到了凝固过程中液相（ L）到高温铁素体（δ）到奥氏体（γ）的相变温度。在此基础上分析了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变规律,从而建立了304奥氏体不锈钢的低冷速凝固相转变规律曲线—SPT（Solidification phase transforma?tion）曲线。结果表明：对试样进行液氮酒精淬火有效地保留了试样高温时各相的状态。可以清楚的显示在不同冷速下的不同温度淬火时液相和固相的各相成份比例及在不同淬火温度下各成份体积比例的变化。通过研究体积比例变化,可以得到304奥氏体不锈钢在不同冷速下的液相线、固相线及各种反应开始和结束的转变温度（即SPT曲线）。由SPT曲线也可以看出,随着冷却速度的增大,相转变模式会发生变化,相图会向左移动,各相变反应的温度区间减小。     

三元乙丙橡胶基吸油树脂型相变储能材料的相变过程

分别以聚乙二醇(PEG)、石蜡为相变物质,三元乙丙橡胶(EPDM)基吸油树脂为骨架支撑材料,通过吸油树脂对相变物质的吸附作用,制备了高分子固-固相变材料。使用红外光谱和差示扫描量热法对相变材料的结构和相变行为进行了研究;同时,采用偏光显微镜的反射模式对相变材料的动态相变过程进行了观察。研究结果表明:在相变储能材料中,相变物质石蜡与PEG的熔融相转变焓分别为140.8 k J/g和7.5 k J/g;结晶相转变焓分别为137.2 k J/g和2.8 k J/g;在动态升/降温的相转变过程中,可观察到相变物质在吸油树脂网络中的熔体流动/凝固状态;相变过程中相变物质未发生泄漏,具有可逆的相转变特性。     

石蜡微胶囊相变材料与建筑节能

介绍了石蜡相变材料物相变化的特点及其物相变化过程的不定形性，阐述了用微胶囊技术将固-液相变的石蜡转变为固-固相变的石蜡微胶囊的方法。分析了石蜡微胶囊相变材料用于建筑节能领域的现状、存在的问题及其应用前景。     

十八烷/膨润土复合相变储热材料的制备及性能研究

以十八烷为相变材料,膨润土为支撑结构,采用"微波法"与"熔融插层法"相结合制备了十八烷/膨润土复合相变储热材料.采用X射线衍射(XRD)、差示扫描量热分析(DSC)及偏光显微镜(POM)对复合相变储热材料的结构与性能进行了表征.结果表明,十八烷进入膨润土纳米层间导致层间距扩大;复合相变储热材料的相变温度为27.03℃,与十八烷一致;相变潜热为67.22J/g,与质量分数为33.33%的十八烷的相变潜热相当;在发生固-液相变时没有液态十八烷析出.500次加热/冷却循环后,复合相变储热材料的层间距及相变温度没有明显变化,相变潜热减少约3%,证明复合相变储热材料具有良好的结构与性能稳定性.     

共混法制备高分子固-固相变材料及其表征

通过共混法制备了PEG/CDA高分子固-固相变材料,用DSC差示扫描量热法对其相变行为进行了研究,讨论了PEG/CDA质量比对所得相变材料相变行为的影响.结果表明,该材料呈现出固-固相转变特性;其相变温度和相变焓比纯PEG低,并随着PEG含量的增加而升高.     

共混法制备高分子固-固相变材料及其表征

通过共混法制备了PEG／CDA高分子固-固相变材料，用DSC差示扫描量热法对其相变行为进行了研究，讨论了PEG／CDA质量比对所得相变材料相变行为的影响。结果表明，该材料呈现出固-固相转变特性；其相变温度和相变焓比纯PEG低，并随着PEG含量的增加而升高。     

相变材料微/纳胶囊的研制及其在红外隐身中的应用

相变材料微/纳胶囊是利用保护性囊壁包裹相变材料制得的微粒,它们在相变材料历经相转变时可以吸收、储存和释放大量的潜热,而本身温度基本不变。本文综述了相变材料微/纳胶囊的主要制备方法及最新研究进展,介绍了它们在红外隐身中的应用,并展望了其应用前景。     

尿素浆体的制备及其流动特性研究

相变蓄冷浆体材料具有良好的流动性与高蓄冷密度,既可以充当蓄冷材料又可以作为载冷剂输送冷量。冰浆是一种安全高效的蓄冷介质,已广泛应用于蓄冷空调。然而冰浆制备温度低,限制其在空调系统中的能源利用效率。研究发现,对高质量浓度尿素溶液降温冷却可以制备尿素浆体,相变温度范围覆盖空调工况,且相变潜热较高,具有应用潜力。本文针对尿素溶液的热物性和尿素浆体的流动性能进行了实验研究,结果表明：质量浓度为43%~48%的尿素溶液的相变温度为5~12 ℃,潜热为213.7~223.2 J/g;尿素溶液（C＞32.5%）在液相线处密度随溶液质量浓度的增大而增大,运动黏度变化则相反;尿素浆体流动特性受固相率、Re的影响,不同工况下呈涨塑性流体特征。     

Experimental study of thermal conductivity of solid and liquid phases at the phase transition

An experimental method for the determination of the thermal conductivity of a pure material at its freezing melting point has been developed. In the present investigation. this method is discussed further by studying the effective thermal conductivity of the frozen as well as the thawed state of a wet porous material. and of solid and liquid benzene at the interface. The method involves the study of the transient propagation of the freezing or melting zone through the specimen as well as the steady state of the freezing melting process. The method makes use of the heat of transition as the heat flow, and it enables the interlace to act as a heat transfer surface, thus incorporating realistic features of the phase change process. Compared with data from the literature. the experimental results for benzene agree within 2% for the solid phase and within 3% for the liquid phase. when some precautions are made to avoid free convection. The experimental effective thermal conductivity of the packed bed is compared with data from a numerical analysis: the results agree within 4%, indicating that the method is applicable also for measurements on heterogeneous materials.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.On leave from Central South University of Technology, 410083 Changsha, P.R. China.     

EVA用于低熔点石蜡的定形支撑材料的研究

采用一定配比的固态与液态的混合熔融石蜡作为相变材料、EVA树脂作为支撑材料制备定形相变材料。研究了混合石蜡的热性能、选择不同型号EVA树脂时石蜡含量与材料相变焓之间的关系以及石蜡含量的临界值、定形相变材料的热稳定性和微观形貌。结果显示使用VA含量较低的EVA14/2树脂,可以提高石蜡包裹量并增加EVA树脂与石蜡之间的结合力,从而制成具有较高相变焓和具备良好热稳定性的定形相变材料。     

一种新型复合相变材料导热性能的实验研究

针对相变材料在实际应用过程中交替存在升温液化和降温固化的复杂传热过程,采用JW-Ⅲ建筑材料热流计式导热仪,分别对升温和降温过程中处于固态、混合态、液态的新型复合相变材料导热性能进行了测试和分析。研究结果表明,复合相变材料在加热和冷却过程中的导热系数随温度的变化存在明显的规律性差异,导热系数在混合态时差值达到20%;升温过程中,复合相变材料在混合态和液态时的导热系数值相差不大,但与固态时相比有明显减小;降温过程中,在液-固相变的过程中导热系数随温度减小而增大,有利于加速相变材料的固化。     

水平冷表面上结霜发生随机性研究

水蒸气在冷壁面上的结霜是制冷、低温领域普遍存在的问题。过饱和的水蒸气有两种相变途径，一种是气液固相变；一种是直接气固相变。气液固相变经历气液相变和液固相变两个阶段，实验研究表明其发生具有随机性。在前人实验研究的基础上，从理论上给出了液珠半径随时间的增长规律，并进一步得到了冷壁面自然对流情况下结霜发生概率随时间的变化关系式。     

Crystalline-amorphous phase transition of hyperbranched polyurethane phase change materials for energy storage

Hyperbranched polyurethane solid–solid phase change material (HB-PUPCM) has been prepared via a two-step process. The phase transition behaviors and morphologies of these HB-PUPCM films were investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarizing optical microscopy (POM). PEG soft segment in the polyurethane was found to be crystalline at room temperature. However, when the temperature was raised to PEG’s melting point, polyurethane did not melt into the liquid state as in the case of pure PEG but changed to an amorphous solid state. In HB-PUPCM, PEG’s molecules probably are tied to the hard segment chain so strongly by the chemical bonds that they cannot change to a liquid state but change to the amorphous state in the transition processing.     

界面聚合法制备微胶囊相变材料的试验研究

以相变石蜡为芯材,廉价的聚脲和聚氨酯为壁材,采用界面聚合法制备了单层和双层壁材微胶囊相变材料,并用差示扫描量热仪(DSC)和TG分析仪分别对所制备的单层壁材微胶囊和双层壁材微胶囊进行了测试.结果表明,与同条件下制备的单层壁材微胶囊相比,双层壁材微胶囊在合成过程中反应充分、产率较高,在室温环境下相变温度为19.02℃,且保持了较高的相变潜热(79.9J/g),适合于建筑用相变材料.     

Numerical investigation on the natural convection effects in the melting process of PCM in a finned container using lattice Boltzmann method

This work presents a numerical study to investigate the melting process inside a finned rectangular container of phase change material. This issue is interested to know what will happen in the presence of fins, which increase the rate of heat transfer and immerse the solid body through the liquid phase. Momentum exchange between the liquid and solid phases necessitates to consider the immersed boundary condition on the solid–liquid interface. This procedure is done by considering the direct-forcing scheme in the lattice Boltzmann framework. In this regard, velocity and temperature fields are obtained using the multi relaxation time model. To track the solid–liquid interface, a set of Lagrangian points is intended on the boundary of the solid phase. Also, the phase change process is modeled by applying the energy conversion on the finite control volume around these points. Results include melting process for three states: assumption of pure conduction, considering the effects of natural convection around the fixed solid body and natural convection through the free solid phase. Comparing results of melting history and solid–liquid interface position in those states specifies the importance of momentum exchange between solid and liquid phases, in which the forced exerted by the fluid flow accelerates the melting process.     

液相/微胶囊复合体系相变特性实验研究

相变微胶囊材料因其环保性与经济性的优势,已成为相变储能领域的研究热点,但其导热性能过低,严重限制了相变微胶囊材料的推广与应用。本文分别用无水乙醇和蒸馏水填充于微胶囊的颗粒间隙中,获得复合相变体系,研究了无水乙醇和蒸馏水体积分数分别为20.0%、40.0%、60.0%时复合体系相变特性。实验结果表明,相比于空白体系,两液体填充复合体系的相变速率均有明显提高,无水乙醇/微胶囊复合体系相变速率提升了87.5%~266.7%,微胶囊/蒸馏水复合体系提升了125.0%~368.8%。蒸馏水对微胶囊材料的强化效果优于无水乙醇,同时两复合体系的相变速率均随着填充液体体积分数的增加而上升。研究结果对微胶囊相变强化技术的发展提供了理论指导。     

Modeling of ice formation in porous solids with regard to the description of frost damage

The freezing and thawing of liquid in porous media in connection with the question concerning the frost durability of solid materials is an important subject for discussion in civil engineering. Each construction or body which is in contact with liquid and frozen water is criticized by its resistance to the environment. The durability concerning frost attacks of a building material is affected by its porosity and the pore size distribution. The ice formation is a phenomenon of coupled heat and mass transport in freezing porous media, and is primarily caused by the expansion of ice in connection with hydraulic pressure. The volume increases due to the freezing front inside the porous solid. Taking into account the aforementioned effects in porous materials, a simplified macroscopic model within the framework of the Theory of Porous Media (TPM) for the numerical simulation of initial and boundary value problems of freezing and thawing processes of super saturated porous solids will be presented. The phase change between the ice and the liquid phase is modeled by different real densities of the phases.     

微胶囊相变蓄冷材料的制备及其性能研究

阐述了微胶囊相变蓄冷材料的制备方法及其性能。采用复合凝聚法制备了微胶囊相变蓄冷材料。用明胶和阿拉伯胶作囊材、十四烷作芯材,使用示差扫描量热仪(DSC)来测定蓄冷材料的熔化温度、熔化潜热、凝固温度、凝固潜热,用热重分析仪(TG)测定其热稳定性,并用扫描电镜(SEM)观测了材料的微相结构。测试结果表明,该相变蓄冷材料具有较高的相变潜热和较好的热稳定性,可用作空调的蓄冷材料。