【作者】 李建立；

【导师】 薛平；

【作者基本信息】 北京化工大学 ， 机械设计及理论， 2009， 博士

【摘要】 相变材料（PCM）在发生相态变化时能吸收/释放大量潜热,而自身温度保持不变或只在很窄的范围内变化。近年来世界各国的研究者对无机、有机、无机/有机混合PCM进行了广泛研究。从相变温度和相变潜热角度考虑,工业化前景较好的低温PCM均为固-液PCM。这类PCM在使用中有液相产生,必须设计专门的容器或采用合适的包封材料对其进行封装,其中采用不同的高分子材料作为基体,对石蜡类固-液PCM进行包封,制备各种定形相变材料（FSPCM）的相关研究是一个热点。本文首次提出并制备了一种新型聚合物基FSPCM,该材料是以木质纤维/热塑性树脂的复合体系为基体,通过在其中添加微胶囊化相变材料（MEPCM）及必要的助剂,经模压加工而成的复合材料。围绕新型聚合物基FSPCM的制备和应用研究,主要做了如下工作:①新型聚合物基FSPCM的制备及性能表征以木粉/高密度聚乙烯（HDPE）复合体系为基体,在其中添加不同含量的MEPCM、不同热导率的改进材料、界面改性剂及其它加工助剂,通过模压法制备出十五种定形相变板材样品。用扫描电子显微镜（SEM）观测了定形相变板材的微观形貌,微观照片表明所制备的定形相变板材的各组分在体系中分布均匀,特别是板材试样中的绝大部分MEPCM颗粒仍然完好,从而证实了模压法制备新型FSPCM的可行性。用差示扫描量热仪（DSC）测定了MEPCM和新型FSPCM试样的相变温度、潜热和比热。结果表明:将MEPCM加入木粉/HDPE复合体系,通过模压法制备新型聚合物基FSPCM,不会改变MEPCM原有的相变温度,所得FSPCM的潜热与MEPCM的添加量成正比,当MEPCM含量达到25wt%左右时,FSPCM的潜热约为28kJkg^-1,与国内外同类研究相比处于同一水平。冻融循环稳定性实验表明所制备的新型FSPCM经历100次冻融循环之后,相变温度和潜热的变化较小,表明其有较好的冻融循环稳定性。热失重分析表明所制备的新型FSPCM具有较好的热稳定性。热导率测试结果表明,添加不同的热导率改进材料均能改善新型FSPCM的导热性,改善程度与添加的材料种类和添加比例有关。力学性能测试结果表明,所制备的新型FSPCM的弯曲强度大于10MPa,弯曲弹性模量大体在600 MPa以上,表面硬度约为60HD,基本能满足对装饰板材力学强度的要求。②根据建筑热平衡原理和相变材料特性建立了描述一个典型房间所有围护内部逐时温度场及室内空气逐时温度的数学模型,根据有限差分法用Matlab6.5编写了模拟程序,并对程序进行了理论验证、程序间对比验证和实验验证。利用该程序可对新型FSPCM板材用做建筑围护结构材料的应用效果进行详细的模拟研究。③用上述程序,综合考虑多种因素,特别是电热膜的不同间断运行模式以及蓄热层厚度,对新型FSPCM作为电加热地板辐射采暖系统（以下简称电地暖系统）蓄热层的室温调控效果、节能效果和经济性做了较全面的参数化研究。结果表明:当气象条件、房间朝向、围护结构热工性能及蓄热层自身热物性等确定时,电热膜运行模式和蓄热层厚度对新型FSPCM作为电地暖系统蓄热层的应用效果影响显著。④针对新型FSPCM用作电地暖系统蓄热层时的热物性优化问题,提出了两种优化方法,即稳态计算法和动态模拟法。利用这两种热物性优化方法对将特定厚度的新型FSPCM用作电地暖系统蓄热层时的热物性进行了优化,得到了有意义的结果。将上述两种优化方法结合使用,可为MEPCM的研发、新型FSPCM板材的配方设计提供理论指导,并可为电地暖系统的设计施工提供理论依据。⑤新型FSPCM工业化前景分析新型聚合物基FSPCM基体材料绿色环保、价廉易得,制备方法及工艺可行,产品应用面广,有较好的工业化前景。但要实现新型FSPCM的工业化生产与应用,还需要解决一些关键问题。比如开发出不同相变温度、高相变潜热、冻融循环稳定性好、耐热性好的MEPCM,优化新型FSPCM的配方和制备工艺。更多还原

【Abstract】 Phase change materials （PCM） absorb and release considerable latent heat when they change their phase state over a narrow range of temperature. In recent years, researchers around the world performed comprehensive studies on inorganic, organic and inorganic-organic composite PCM. From the phase transition temperature and latent heat point of view, low-temperature solid-liquid PCM have a better prospect for industrialization. To avoid the leakage of liquid PCM during applications, containers designed specifically or packaging materials are necessary for the encapsulation of solid-liquid PCM. Related studies of various polymer-based form-stable phase change materials （FSPCM）, in which different polymer materials and paraffin wax-type solid-liquid PCM are used as bulk materials and operation materials, respectively, are a hot spot.In this paper, a novel polymer-based FSPCM, which comprises micro-encapsulated PCM （MEPCM） as the latent heat storage medium and wood flour/high density polyethylene composite as the matrix, was put forward and prepared by blending and compression molding method for potential latent heat thermal energy storage applications. Different inorganic materials with high heat conductivity were added to improve the thermal conductivity of prepared polymer-based FSPCM. The main research efforts devoted to the preparation and application studies of novel polymer-based FSPCM are summarized as follows.①Preparation and characterization of novel polymer-based FSPCMFifteen novel polymer-based FSPCM plates were prepared, and their microscopic pattern, thermo-physical properties, thermal stability and mechanical properties were characterized by using scanning electronic microscope （SEM）, differential scanning calorimeter （DSC）, thermogravimetic analysis （TGA）, thermal conductivity measuring apparatus, universal material testing machine and hardness tester.SEM images reveal that the prepared FSPCM plates have homogeneous constitution and most of MEPCM particles in them were undamaged. Therefore, it is feasible to prepare novel polymer-based FSPCM by blending and compression molding method.DSC was used to test the phase change temperatures, latent heats and specific heats of MEPCM and FSPCM plates. DSC results show that: 1) novel polymer-based FSPCM have identical phase change temperatures with MEPCM and their latent heats linearly increase with the increase of weight fraction of MEPCM. The FSPCM plates with about 25wt% MEPCM have the latent heat of about 28kJkg^-1. Thermal cycling test indicates the form-stable PCMs have good thermal stability although it was subjected to 100 melt-freeze cycles.TGA results show that prepared FSPCM plates have good thermal stability.The results of heat conductivity test indicate that micro mist graphite, iron wire and their compounds can be used to improve novel FSPCM plates’ thermal conduction performance. Different weight fractions of these materials with high heat conductivities lead to different improvement effects.The results of mechanical property test show that the flexural strength, flexural modulus and surface hardness of prepared FSPCM plates are above 10 MPa, 600 MPa and 60HD. It can be said that the novel FSPCM plates have goodish mechanical properties for practical applications such as energy efficient building materials.②A mathematic model, based on building heat balance and features of phase change heat transfer, was developed to describe the hourly temperature field of a typical room. A special simulation program was established in Matlab6.5 according to finite difference method. The program was verified by theoretical, contrastive and experimental methods, respectively. By the simulation program, the application effects of using prepared FSPCM as building envelope materials （e.g. floor, wall and ceiling boards） can be comprehensively studied with parameterization.③The effects of room temperature control, energy-saving and cost-reduction of applying novel FSPCM plates as the thermal storage layer （TSL） of an electric floor heating system （EFHS） were analyzed by the above-mentioned simulation program, taking into various factors （especially the operation mode of the EFHS and the thickness of prepared FSPCM plates）. Simulation results show that different operation modes of the EFHS and thicknesses of prepared FSPCM plates lead to different application effects for the same other parameters such as weather conditions, typical room’s orientation, thermal characteristics, FSPCM plates’ thermophysical properties.④Two optimization methods of FSPCM plates’ thermophysical properties were presented. One is the steady-state calculation method and the other the transient-state analogue method. By the two methods, preferable ranges of thermophysical properties （phase change temperature, latent heat, phase change radius and heat conductivity） of FSPCM plates used as the TSL were determined. These two optimization methods can be used to provide guidances for the R&D of MEPCM, the recipe modification of novel FSPCM plates and design-construct of EFHS.⑤Industrialization prospect analysis of novel polymer-based FSPCMs Novel polymer-based FSPCM plates’ bulk materials are reproducible and/or inexpensive. The preparation method is feasible. And novel polymer-based FSPCM have widespread potential applications. Therefore, it is possible and worth to come true the industrialization of the novel polymer-based FSPCM. To realize that, some key problems such as developing MEPCM with different phase change temperatures, high phase change enthalpies, good thermal cycling and thermal stabilities, optimizing the recipes and preparation technologies must be settled.更多还原