基于相变材料的电子元件的散热性能

对比研究了无石蜡、纯石蜡以及石墨/石蜡复合材料三种不同填充状态的散热器在电子元件热管理中的性能,通过实验测量了功率变化时电子元件基板表面温度及散热器表面温度场的变化情况。研究结果表明添加石蜡、石墨/石蜡复合材料能缩短电子器件启动后温度场稳定的时间,温度变化速率有所下降;当功率突然增大时,填充石蜡、石墨/石蜡复合材料的散热器与芯片结合处温度升高值较小、变化较为平缓,可有效抑制热冲击对电子元件的影响。在散热过程中,填充了石蜡、石墨/石蜡的散热器表面温度变化更为平滑,有利于延长散热器的使用寿命。     

相变温控应用于电子设备的抗热冲击性能研究

相变温控是利用相变材料的相变过程以实现对物体温度控制的方法。以高热导率和储热密度的膨胀石墨/石蜡复合材料制作储热材料器件,构建了基于相变温控的电子器件散热模拟实验系统。研究在3种波动热负荷条件下,模拟芯片的表面温度随时间的变化情况,并与同型号传统散热器比较,分析相变温控对电子器件瞬态热管理的影响规律。实验结果表明,在同等条件下,相变温控散热实验系统的抗热冲击性能约为传统散热系统的1.4倍。将复合相变材料应用于电子器件的瞬态热管理中,可以降低电子设备的表面温度、减小温度波动幅度,保证电子电器设备运行的可靠性和稳定性。     

高孔隙率泡沫铜强化相变材料熔化特性

为了研究纯石蜡与泡沫铜/石蜡相变复合材料吸热熔化性能的不同,探究泡沫铜对石蜡熔化换热过程的影响,本文对纯石蜡和孔隙率为0.98的高孔隙率泡沫铜/石蜡复合材料的相变熔化过程进行了可视化实验研究,并数值模拟分析了纯石蜡及泡沫铜/石蜡复合材料熔化过程。结果表明：复合材料与纯石蜡的液相率变化出现交点,即临界液相率值,此时复合材料具有的液相占比与纯石蜡液相占比相同;泡沫铜的填充能明显改善纯石蜡传热系数低的问题,加快相变材料的整体熔化速率,当热通量为1200W/m²时,孔隙率为0.98的泡沫铜填充使纯石蜡完全熔化时间缩短了约12.5%,并使整体温度分布更均匀,改善热分层现象,且复合材料最大温差比纯石蜡最大温差低约27.5K。     

膨胀石墨基相变储能材料的研究

利用膨胀石墨孔隙结构的吸附性能,制备了石蜡/膨胀石墨、聚乙二醇/膨胀石墨、十四醇/膨胀石墨相变储能复合材料,用差示扫描热量法研究了材料的热性能.结果表明,复合材料的相变潜热随着石蜡、聚乙二醇、十四醇含量的增加而增加.复合材料的导热性能随着石蜡、聚乙二醇、十四醇含量的增加而小.膨胀石墨的多孔结构对石蜡、聚乙二醇、十四醇有很好的吸附性能,石蜡、聚乙二醇、十四醇在固一液相变时,未见有液态石蜡、聚乙二醇、十四醇的渗出.     

膨胀石墨相变储热复合材料的制备及性能研究

利用石墨高温膨胀得到多孔高吸附性膨胀石墨,吸附石蜡相变材料,制备了膨胀石墨石蜡相变储热复合材料。采用扫描电镜、差示扫描量热分析对复合材料的结构和性能进行了表征,研究了其储热释热行为。结果表明,在900℃时保持32 s膨胀后可得到适宜的膨胀石墨,吸附适量石蜡时仍保持定型特性,石墨的添加改善了复合材料的导热性能,提高了相变...     

采用相变材料冷却的动力电池组的散热性能

使用石蜡/石墨相变复合材料设计了单体电池和电池组,开展了动力型镍氢电池组散热的实验。通过测定电池在不同电流下放电过程中的温度变化,研究和比较了分别采用相变冷却技术与空气换热冷却技术的电池散热效果;并初步优化了石蜡/石墨复合相变材料的质量配比。实验结果表明,在1C放电倍率下,采用相变材料冷却相对于空气自然和强制对流冷却,电池温升分别降低14～18 ℃以及9～14 ℃。石蜡与石墨质量配比在4∶1时,电池组冷却效果达到最佳。相变材料填充的电池经过充放电循环后,电池性能没有显著劣化。     

石墨/炭黑/EPDM复合材料的性能研究

研究石墨/炭黑/EPDM复合材料的物理性能、动态力学性能和导电性能.结果表明:石墨对炭黑填充EP-DM复合材料具有补强作用,并显著提高其导电性能;石墨/炭黑/EPDM复合材料的电导率-压力曲线表现出“山峰”形变化趋势,升高温度或增大石墨用量时该峰向低压力区移动;石墨用量越大,复合材料电导率的温度依赖性越强,石墨粒子滑移...     

PP/盘状石墨纳米复合材料的非等温结晶动力学

熔融共混制备了不同填充份数的PP/GNP(聚丙烯/盘状石墨)纳米复合材料,采用DSC结合Avrami方程的Jeziorny法和Mo法研究了PP及PP/GNP纳米复合材料的非等温结晶动力学,结果表明:GNP的加入提高了PP的结晶温度Tp,而结晶速率则随GNP填充份数的变化而变化,在低填充含量下,GNP的加入使PP的结晶速率提高,当GNP填充含量为20%时,PP的结晶速率明显降低。     

原位聚合法制备环氧树脂/石墨复合材料的性能研究

采用原位聚合法制备了环氧树脂/石墨复合材料,并对其进行热重(TG)、扫描电镜(SEM)和力学性能分析。结果表明,环氧树脂/石墨复合材料的邵氏硬度和抗弯强度随石墨含量而变化,当其含量为17.44%(质量分数)时,两者出现最大值,抗弯强度达到22.4 MPa,邵氏硬度达到5.21 HD;石墨的加入也使复合材料的电性能和热性能得到提高,其耐热温度可达350℃。     

PE/多层石墨导热复合材料的制备与性能

PE、GPE为基材,多层石墨、石墨为填料,采用机械混炼法制备高导热塑料复合材料。SEM分析表明PE/多层石墨比GPE/多层石墨复合材料的插层效果更好。研究填料对复合材料的热导率和热稳定性的影响。结果表明:导热复合材料的热导率随填料填充量的增大而增大,多层石墨的填充量达到100%时,热导率为4.15 W.m-1.k-1。并且在相同填充量下PE/多层石墨较之GPE/多层石墨、PE/石墨、GPE/石墨的导热率更高。TGA分析表明:填充多层石墨、石墨的导热塑料复合材料热稳定性高于未填充的PE。经研究提出,形状比(径厚比)大和导热率高的导热填料更易形成导热网链;为了不影响导热填料的分散性,可先使基体材料与填料先混合均匀再增加其韧性、黏度等。     

膨胀石墨/石蜡复合相变材料的导电及发热特性

采用混合搅拌方法制备膨胀石墨（EG）/石蜡复合相变材料,测试分析了EG含量、施加电压与EG/石蜡复合相变材料体积电阻率的关系,研究了直接自发热和正温度系数（PTC）电阻发热时复合相变蓄热单元的发热特性。结果表明,随着EG含量或施加电压的增大,复合相变材料体积电阻率逐渐减小;施加电压对样品体积电阻率的影响与复合相变材料中EG含量有关,EG含量越高,施加电压对复合相变材料体积电阻率的影响越明显。当施加电压为4.0V时,EG质量分数分别为4%、5%、8%的复合相变材料体积电阻率分别只有0.5V时的0.481倍、0.185倍、0.068倍。基于复合相变材料导电特性,直接负载电压可实现复合相变材料电热转化和相变蓄热;结合PTC电阻发热可灵活控制复合相变蓄热单元加热功率,实现其快速充热。     

80#石蜡/膨胀石墨定形复合相变材料的特性表征与分析

以80^#石蜡为相变材料,利用不同粒径膨胀石墨的多孔隙结构,以多层吸附、模压法压制方式制备了80^#石蜡/膨胀石墨定形复合相变材料。通过循环融冻实验分析了80^#石蜡的热稳定性和循环稳定性,滴定滤纸渗漏实验确定了不同组分复合相变材料的渗漏率。采用差示扫描量热仪(DSC)、扫描电子显微镜（SEM）、Hot Disk热常数分析仪等仪器对所制备复合相变材料的相变潜热、多孔基吸附结构、热导率、渗漏率等特性进行了分析。结果表明：当膨胀石墨的添加质量分数达到整体组分的8%时,复合定形相变材料的相变温度为80.86℃（吸热）和76.08℃（放热）,相变潜热为130.12kJ/kg,且渗漏率小于0.3%。制备的复合定形相变材料具有形状稳定、渗漏率低、蓄热密度高的特点,且具有较长的使用寿命。     

石蜡石墨粉复合相变材料在温室大棚中的控温效果研究

通过将复合相变材料应用于温室大棚中,达到控制温室温度波动幅度的目的.即利用相变材料在使用环境温度高于相变温度时可吸收热量,低于相变温度时可释放热量的能力,起到调节周围环境温度的作用.对比了石蜡以及加入不同比例石墨粉的石蜡石墨粉复合相变材料的导热性能;研究了加入复合相变材料的温室模型和对比模型的温控性能.结果表明:加入石墨粉,提高了石蜡的导热性能;加入相变复合材料的温室模型室内温度波幅小,控温效果优于对比温室;墙体储(放)热能力优于对比温室.     

Thermal and mechanical behavior of unsaturated polyesters filled with phase change material

Samples of commercial unsaturated polyester (UPE) resin, filled with phase‐changeable fillers (PCMs), were prepared, and the thermal and mechanical properties of the cured samples were examined. Fillers chosen were paraffin and Wood's metal. Samples were prepared by making dispersions of these fillers in liquid unsaturated polyester followed by curing with methyl ethyl ketone peroxide (MEKP) and conaphtanate and rigid thermoset samples filled with PCM particles were obtained. The thermal and mechanical behaviors of such a filled composite around the melting points of fillers are very interesting. Effects of varying proportions of PCM on mechanical and thermal properties of final products were examined. The samples show thermal melting behavior without undergoing a change in physical state. Decreases in the maximum working temperature from 75 to 53°C for metal‐filled samples and from 75 to 43°C for paraffin‐filled samples were observed by using dynamic mechanical thermal analysis. Differential scanning calorimetry indicated that heat absorption of paraffin samples were higher than that of metal‐filled samples. For paraffin‐filled samples, heats of fusion were 3.44 cal/g for 10% filled sample and 6.35 cal/g for 20% filled sample. For Wood's metal‐filled samples, heats of fusion were 1.18 cal/g for 10% metal‐filled sample and 1.54 cal/g for 20% metal‐filled sample. Surface hardness was tested with Shormeter D. Surface hardness of metal‐filled composites varied from 86 to 34 shore D at 21°C and 80.6 to 35 shore D at 80°C. For paraffin‐filled samples, surface hardness changed from 86 to 42 shore D at 21°C and from 80.6 to 13 shore D. Morphology of the samples was determined by scanning electron microscopy, of the crack surfaces. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 832–838, 2006     

石蜡油对聚丙烯发泡性能的影响研究

通过双螺杆挤出制备了聚丙烯(PP)/石蜡油共混材料,研究了石蜡油用量对共混物流变性能和热性能的影响;在自制的超临界CO2动态发泡模拟机上制备了PP发泡材料,研究了发泡温度对PP发泡材料的影响。结果表明,加入石蜡油后,PP结晶度有了较大的提高;当石蜡油质量分数为1%时,发泡样品的表面更加光滑,泡孔密度增加;当发泡温度为130℃时,PP/3%石蜡油共混材料发泡效果较好,泡孔分布更加均匀。     

固-液相变传热强化过程研究进展

相变热控技术是从20世纪60年代航天热控技术演变而来,通过相变将热量储存或释放从而达到控制温度的目的。但是由于部分相变材料的导热系数低,使系统的储能和释能时间增加,不利于有效控制系统的温度。这种系统只适用于功率不高且功率周期性变化的场所,针对这个问题,国内外学者进行了大量研究,文章对近几年国内外强化相变传热的大量研究进行了综述。介绍了三种主要的强化传热方法,分别是泡沫金属、金属固体和金属翅片、膨胀石墨。并探讨了强化相变传热中存在的问题。     

Mechanical and tribological properties of glass–epoxy composites with and without graphite particulate filler

The objectives of this research article is to evaluate the mechanical and tribological properties of glass‐fiber‐reinforced epoxy (G–E) composites with and without graphite particulate filler. The laminates were fabricated by a dry hand layup technique. The mechanical properties, including tensile strength, tensile modulus, elongation at break, and surface hardness, were investigated in accordance with ASTM standards. From the experimental investigation, we found that the tensile strength and dimensional stability of the G–E composite increased with increasing graphite content. The effect of filler content (0–7.5 wt %) and sliding distance on the friction and wear behavior of the graphite‐filled G–E composite systems were studied. Also, conventional weighing, determination of the coefficient of friction, and examination of the worn surface morphological features by scanning electron microscopy (SEM) were done. A marginal increase in the coefficient of friction with sliding distance for the unfilled composites was noticed, but a slight reduction was noticed for the graphite‐filled composites. The 7.5% graphite‐filled G–E composite showed a lower friction coefficient for the sliding distances used. The wear loss of the composites decreased with increasing weight fraction of graphite filler and increased with increasing sliding distance. Failure mechanisms of the worn surfaces of the filled composites were established with SEM. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2472–2480, 2007     

Preparation and properties studies of paraffin/high density polyethylene composites and phase-change coatings

The form-stable paraffin/high density polyethylene (HDPE) composites and phase-change coatings were prepared and characterized in this study. The paraffin acts as thermal absorbing material and HDPE serves as the supporting material, which provides structural strength and prevents the leakage of melted paraffin. Scanning electronic microscope (SEM) showed that the paraffin is dispersed uniformly into porous network of HDPE. Differential scanning calorimeter (DSC) determined the melting temperature and heat storage capacity of the composite piece to be 49.6 °C and 150.88 kJ/kg, respectively. Moreover, results indicated that the composite pieces showed better thermal stability than composite powders after 6 temperature cycling experiments. The phase-change coatings with 40 wt% composites as functional filler showed good adhesion strength and shock resistance, and could decrease the surface temperature obviously comparing with nude Al alloy plates.