定形相变材料的有效导热系数

为更有效地预测定形相变材料的有效导热系数,以高密度聚乙烯/石蜡定形相变材料为对象,在分形理论的基础上,考虑空腔的分布和石蜡不同相态下的体积变化,建立一种新的导热系数模型——分形-空腔模型。采用准稳态平板法对此模型进行验证,探讨多个参数对有效导热系数的影响。结果表明:该模型的预测值更加符合实际。提高石蜡含量、体积收缩率、初始空腔率、分形维数等参数均会影响定形相变材料的导热系数,初始空腔率对熔融状态下的热导率的影响强于凝固状态下的影响。     

微纳米粒子对辛酸-肉豆蔻酸相变储能体系热物性的影响

该文通过添加3组同族(镍、铝、铜)亚微米级金属、纳米金属及纳米金属氧化物改善其传热性能,制备可用于空调蓄冷系统的新型相变储能材料;通过步冷实验、差示扫描量热法(DSC)及瞬态平面热源法(Hotdisk)对比添加剂对OA-MA在过冷度、相变温度、相变潜热、导热系数及热扩散率等方面的影响,研究添加剂种类与颗粒尺寸对上述热物性的影响规律;利用Maxwell及Zimmerman公式对比不同质量比例的纳米氧化铜(CuONP)对材料导热系数的影响,研究纳米流体传热传质机理,数据拟合得出其拟合公式。     

季戊四醇与三羟甲基乙烷相变材料蓄热性能研究

对一类可用于太阳能中温蓄热的有机相变材料性能进行实验分析。相变蓄热材料具有储热密度大、温度波动小等优点,但也存在导热系数低、过冷度较大的问题,对相变材料进行复合,能有效改善其相变特性与导热性能。利用高温融化-混合的方法制备季戊四醇(PE)与三羟甲基乙烷(PG)的混合材料,使用DSC仪器分析相变温度与相变潜热,同时研究不同形核剂对混合材料的相变温度、过冷度的影响。利用压制成型—融化吸附—冷却的方法制备膨胀石墨与PE、PG的复合相变材料,用激光导热系数测试仪测试复合相变材料的导热性能。结果表明,PE与PG混合相变材料的相变温度区间基本在25℃以上,过冷度约15℃,膨胀石墨作为形核剂,使过冷度有一定减小。增加复合相变材料中膨胀石墨的含量能提高材料各个方向的导热系数。     

新型定形板状相变材料的蓄/放热特性

对填充了新型定形板状相变材料的蓄热槽的蓄／放热特性进行了数值计算分析和实验比较。根据数值计算，对影响蓄热槽蓄／放热特性的主要因素——相变材料的几何尺寸、相变材料的导热系数、流体流速、对流放热系数、相变材料填充率等的影响规律进行了分析研究，计算出了蓄热槽内温度分布随时间的变化；并在实验台上测试了蓄热槽初始温度、流人和流出蓄热槽流体温度、作为蓄热体的相变材料测点温度随时间的变化，计算结果与实验结果具有较好的一致性。     

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.     

基于石墨烯气凝胶的定形相变材料储热性能研究

使用石墨烯气凝胶(graphene aerogel,GA)为导热骨架,十六醇作为相变材料,制备出一种用以储热的定形相变材料。利用FITR、XRD、SEM、激光闪光法和DSC等手段对样品的微观形貌、化学结构以关键热物性进行了表征,同时也测试了样品实际吸/放热的速率。结果表明,GA的多孔结构可以有效防止相变材料的泄露。同时,高导热的石墨烯在相变材料中建立起额外的导热通路,使得样品的导热系数提高了20%。重复吸放热50次后发现,样品的融化/凝固焓并没有因为GA的加入明显下降,分别为229.2和229.5kJ/kg。吸/放热温度曲线表明,在以导热为主的传热过程中,拥有更高导热系数的定形相变材料比纯十六醇具有更快的融化/凝固速率。而在自然对流为主的传热过程中,由于GA较强的毛细作用,十六醇的流动性被削弱,定形相变材料的融化/凝固速率低于纯十六醇。     

石墨泡沫/共晶盐复合相变材料制备

选择KNO3/Na NO3二元体系按照质量比4∶6制备共晶盐,对共晶盐进行了熔点及熔化潜热的测量;将石墨泡沫这一新型材料作为强化基体,共晶盐作为相变材料(PCM),采用熔融浸渗法制备了适用于太阳能热发电系统储能装置的石墨泡沫/共晶盐复合相变材料。采用扫描电镜对复合相变材料表面的微观结构进行了表征,并对其熔点、潜热、等效导热系数等热物性参数进行了测试。结果表明:共晶盐与石墨泡沫复合效果比较理想;复合前后共晶盐的熔点和潜热几乎没有发生变化;复合相变材料的等效导热系数得到了显著提升,石墨泡沫对相变材料起到了导热强化作用,满足高温蓄热的要求。     

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。     

硬脂酸丁酯/多孔石墨定形相变材料的实验研究

本文利用多孔石墨的毛细管作用吸附硬脂酸丁酯制成了一种定形相变材料,利用DSC研究了硬脂酸丁酯质量含量不同的定形相变材料的相变温度、相变潜热和热稳定性,得出硬脂酸丁酯含量的临界值。研究结果表明:硬脂酸丁酯和纳米多孔石墨形成的定形相变材料相变温度合适、相变潜热较大、热稳定性好,是适合于在建筑墙体中使用的相变材料。     

相变材料相变点温度热物性的测试及误差分析

固-液相变过程中移动的相界面曲线与两相热物性如比热、密度、导热系数以及相变潜热是密切相关的。本文提出通过测定相界面的移动速率来确定相变材料固-液相变温度点导热系数等多个热物性参数的方法，并设计了相应的测试装置。对测试系统的测量误差进行了定量分析，发现采用数值计算与实验相结合的方法测试的系统误差不超过3％。利用研制的测试系统对几种材料的导热系数和热扩散系数进行了测定，得到了满意的结果，表明本文所提出的测试方法是可信的。     

Influence of additives on thermal conductivity of shape-stabilized phase change material

Shape-stabilized phase change material (PCM) is a kind of novel thermal energy storage material. Its thermal conductivity is low, which limits its application in many conditions. In this paper, additives with high thermal conductivities were doped in it to improve its thermal conductivity. The thermal conductivity was measured by a thermal probe at room temperature. The experimental results show that the thermal conductivity of the shape-stabilized PCM can be improved greatly by adding exfoliated graphite. An empirical equation was developed for calculating the effective thermal conductivity of the shape-stabilized PCM with different mass fraction of graphite additive. By using the so-called numerical element method, a theoretical equation was obtained for predicting the effective thermal conductivity, which agrees well with the experimental results. The empirical equation and the theoretical prediction are useful for “designing” and controlling the thermal conductivity of the shape-stabilized PCM.     

良导热、形状保持相变蓄热材料的制备及性能

将石蜡与一热塑弹性体SBS复合制备了在石蜡熔融状态下仍能保持形状稳定的复合相变蓄热材料，复合材料保持了石蜡的相变性，相变潜热可高达纯石蜡潜热的80%，在复合相变材料中加入膨胀石墨后，热传导性有了显著提高，其放热时间比纯石蜡缩短了61%。     

Thermal performance of shape-stabilized phase change paraffin wallboard

This paper presents thermal performance of shape-stabilized phase change material (PCM) wallboards and common wallboard. Shape-stabilized PCMs consist of paraffin and high-density polyethylene as support materials. The wallboards were prepared by shape-stabilized PCMs and grout with the building materials in mass proportions of 5%, 10%, and 15%. The phase change temperature of the shape-stabilized paraffin was 27.5 °C and the maximum content of paraffin in the shape-stabilized PCM was 70%. The energy-saving effect and feasibility of shape-stabilized PCM wallboard were compared with those of ordinary wallboards. The results showed that prepared PCM wallboard has good thermal performance and thus it has high potential for the cooling of buildings.     

相变储能堆积床传热特性的研究

基于多孔介质传热理论,建立了储能堆积床的传热模型.在此基础上分析了换热流体流量、温度、单元尺寸、相变材料导热系数和孔隙率等参数对堆积床传热特性的影响.研究表明,提高相变材料的导热系数,增大换热流体温差或减小单元尺寸对堆积床传热速率有明显提高,而提高换热流体流量,增大对流换热系数对传热速率的影响不明显.因而强化相变材料侧的传热过程是提高堆积床传热速率的有效途径.     

Heat transfer enhancement of fatty acids when used as PCMs in thermal energy storage

Phase change materials (PCM) used in latent heat storage systems usually have very low thermal conductivities. This is a major drawback in maintaining the required heat exchange rate between PCM and heat transfer fluid. This paper investigates the enhancement of the heat transfer between PCM and heat transfer fluid, using high thermal conductivity as additives like stainless steel pieces, copper pieces and graphite–PCM composite material. In the experiments, palmitic–lauric acid (80:20) (PL) and stearic–myristic acid (80:20) (SM) were used as PCMs. Test results show that heat transfer enhancement of copper pieces was better at 0.05 Ls^?1 flow rate compared to 0.025 Ls^?1. Using copper as an additive increased the heat transfer rate 1.7 times for melting and 3.8 times for freezing when flow rate was 0.050 Ls^?1. Decreasing the flow rate from 0.050 to 0.025 Ls^?1, increased the melting times 1.3 times and freezing times 1.8 times, decreasing heat transfer rates accordingly. The best result of heat transfer enhancement was observed for the PCM–graphite composite. However, changing the flow rate did not affect the heat transfer rate when graphite was used as additive. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental study on the thermal properties of the phase change material wall formed by different methods

The thermal properties of the shape-stabilized phase change material walls with different structure were studied. The phase change material is composed of paraffin mixture and high-density polyethylene. The walls including concrete and shape-stabilized phase change material were prepared respectively by different methods. Preparation methods include direct mixing method and lamination interpolation method. Heat transfer process in the shape-stabilized PCM walls was studied by comparing with traditional wall. The results showed that the surface temperature and the heat flow through the phase change material walls prepared by different methods are lower than that of traditional wall and the change is small. Energy-saving effect of the shape-stabilized PCM walls prepared by lamination interpolation method is better than that of the shape stabilized PCM walls by direct mixing. Results in this paper can provide the basis for the application of the shape stabilized PCM walls in the buildings.     

Preparation of form-stable carbonates/magnesium oxide-flake graphite composite thermal storage material and its thermal conductivity

以混合碳酸盐为相变材料，以氧化镁为陶瓷基骨架材料，以鳞片石墨为导热增强剂，通过混合烧结法制备出中高温复合蓄热材料。基于XRD和SEM表征分析可知，添加鳞片石墨后复合材料具有较好的化学稳定性，而且由于鳞片石墨的原因复合材料形成较多的孔隙结构。通过分析添加鳞片石墨后复合材料的热物性可知，随着鳞片石墨含量的增加，复合材料的熔点基本不变，而其热导率不断提高。鳞片石墨含量为25%的混合碳酸盐/氧化镁复合材料在250℃和560℃时的热导率分别达到3.88 W/（m·K）和2.52 W/（m·K）。基于微观结构和界面层理论对复合材料的导热增强机制进行了分析与讨论。     

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.     

添加石蜡的相变水泥墙传热性能分析

利用ANSYS有限元分析软件,模拟添加石蜡的相变水泥墙体和普通水泥墙体的传热性能。通过模拟计算,给出普通水泥墙和相变水泥墙在一侧受到热流时另一侧的表面温度和热流的变化规律,并与实验测试结果进行比较;通过对比研究相变墙体和普通墙体的传热性能,分析相变墙的节能效果和可行性;同时求解相变墙体表面恒温时间随导热系数和相变潜热的变化规律。结果显示:数值模拟结果与实验测试结果较吻合,模拟方法可行;与普通墙体相比,相变墙体的温度变化平缓,热流传递出现滞后,热流量小,节能效果较明显;提高相变材料的导热系数和潜热能提高表面恒温时间,有利于相变材料在墙体中的储能效果。     

基于热辨识技术的硅基防热材料高温热导率测量

硅基防热材料是高超声速飞行器防热系统用重要材料之一,但由于硅基防热材料在高温条件下存在着复杂的物理化学变化,使得高温热导率的获取变得困难,这已成为飞行器防热系统精细化设计的主要制约瓶颈。基于热导率辨识方法,设计了一种能够实现硅基防热材料高温热导率测量的试验测量装置,对硅基防热材料在常温~800℃热导率进行了测量,并将测得的热导率外推应用到其他试验状态。结果表明,测得的硅基防热材料高温热导率合理可靠,具有很高的工程精度。该试验测量装置可实现不同温度下热导率的同步测量,测量成本低,效率高,这对其他防热材料的高温热导率测量具有重要的参考价值。