石墨/聚酰亚胺复合材料的热性能研究

以石墨填充聚酰亚胺(PI)复合材料为研究对象,考察了温度和石墨用量对石墨/PI复合材料的比热容、热导率和热扩散系数的影响。实验表明,升温速率、载气N2流速和样品质量是影响PI复合材料比热容的主要因素;PI复合材料的比热容随石墨用量的增加而降低,PI复合材料的热导率和热扩散系数都随石墨用量的增加而增大;随着温度的升高,PI复合材料与无机复合材料的比热容和热导率变化规律相同;而PI复合材料与无机复合材料的热扩散率变化规律却不同。     

改黑碳推进剂比热容和热导率与温度之间的关系

为了解推进剂比热容和热导率与温度之间的关系,用差示扫描量热仪和热常数分析仪测试了不同温度下改黑碳(GHT)推进剂的比热容和热导率,确定了比热容的测量区间,讨论了比热容和热导率随温度的变化规律;并通过回归拟合得到比热容随温度变化的方程式。结果表明,GHT推进剂比热容的测量区间为298~373K,在此区间内比热容随温度升高逐渐增大,且比热容满足相加性原理;热导率随温度升高而减小,主要是受NG熔融蒸发和晶格振动等因素影响。     

咪唑型离子液体热物理性质测量

利用自行搭建的热线法液体热导率和热扩散系数装置测试了两种咪唑型离子液体([C₆mIm][BF₄]和[C₄mIm][BF₄])在不同温度下的热导率和热扩散系数。根据文献报道的密度数据获得了样品的比热容。结果表明:两种离子液体的热导率与温度的相关性不大;两种阳离子结构相似的离子液体热扩散率相近, 热扩散率随温度的升高有明显的变化, 本文认为离子液体内部的离子动量分布与温度紧密相关, 离子间的动量交换随温度的升高而增加, 离子动量分布随温度升高逐渐趋于一致, 离子间碰撞产生的动量交换不再明显改变离子的动量, 导致热扩散率的变化随温度升高而减小。     

纳米SiO_2粒子对低熔点混合硝酸盐热物性影响

为探究纳米粒子对低熔点混合硝酸盐热物性的影响规律,采用高温熔融分散法将平均粒径20 nm的SiO_2纳米粒子以1%(质量)比例直接分散到混合熔盐[Ca(NO_3)_2?4H_2O-KNO_3-NaNO_3-LiNO_3]中得到不同分散条件下的熔盐纳米复合材料。采用同步热分析仪(DSC)与激光闪射仪(LFA)测量熔盐纳米复合材料比热容与热扩散系数,进而得到热导率。分析发现,600 r/s搅拌速率下熔盐纳米复合材料热物性随分散时间(15,45,90,120和150 min)发生明显变化。比热容、热扩散系数和热导率在分散45 min时提高率最大,平均提高率分别为11.5%,12.9%和26.4%。扫描电镜(SEM)观察到熔盐纳米复合材料表面有大量特殊结构(类似于链状或条状)存在。这些具有高比表面积和表面自由能的特殊结构可能是熔盐纳米复合材料热物性提高的关键。     

掺镁碳酸熔盐液体导热特性

为克服碳酸熔盐热导率较低的不足,提出通过向三元碳酸熔盐(Li2CO3-Na2CO3-K2CO3)掺杂金属镁粉来改善导热性能的新思路,采用静态熔融法制备了掺杂1%、2%掺镁碳酸熔盐复合材料。采用扫描电镜-X射线能谱、阿基米德法、差示扫描量热法(DIN比热测试标准)和激光闪光法,分别观察了掺镁碳酸熔盐形貌结构,测量了熔盐和复合熔盐液体的密度、比热容、热扩散系数,最后计算获得复合熔盐液体的热导率。研究结果表明,镁粉的加入改变了纯盐(三元碳酸熔盐)的形貌结构,熔体内形成大量的2~5μm球体颗粒,与纯盐相比,1%掺镁碳酸熔盐液体密度、热扩散系数和热导率都得到增强,液体比热容减小,复合熔盐液体的平均热导率增加了21.67%;2%掺镁碳酸熔盐液体密度、热扩散系数和热导率同样得到增强,虽然复合熔盐液体的比热容减小,但其平均热导率仍然增加了19.07%。1%掺镁碳酸熔盐具有更高的液体密度、热扩散系数和热导率,可作为传热介质在太阳能热发电传蓄热系统推广。     

胶料热物性对微波加热硫化温度场的影响

采用闪光导热分析仪和差示扫描量热仪对异戊橡胶(IR)在硫化过程中的热物性参数进行测量,得出热导率和比热容随温度的变化规律。同时采用ANSYS有限元分析软件对IR进行三维建模,并对其微波加热硫化过程进行数值模拟,得到热导率和比热容恒定或随温度变化等4种情况下胶料内部的焦耳热密度分布和温度分布。结果表明,热导率变化对胶料温度分布影响不大,而比热容变化的影响较大。     

注塑工艺对哑光PC/ABS冲击性能的影响

通过不同注塑工艺对哑光级聚碳酸酯(PC)和丙烯腈–丁二烯–苯乙烯(ABS)共聚混合物进行注塑成型,通过改变不同的注塑条件(注塑温度、模具温度、注塑压力、注塑速度),研究不同的注塑工艺对哑光PC/ABS材料抗冲击性能的影响。研究结果表明,注塑工艺变化,会引起材料冲击性能变化。其中注塑温度与模具温度对结果影响较大,注塑温度240℃,模具温度80℃时,哑光PC/ABS的冲击强度最高;在合适的注塑压力范围内,压力变化对材料冲击影响不大;合适的注塑速度范围内,注塑速度变化对材料冲击影响不大。工艺选择注塑温度240℃,模具温度80℃,注塑压力2.6~6.1 MPa,注塑速度13.9~32.3 g/s时,哑光PC/ABS冲击性能最好。因此,选用合适的注塑工艺可以提高材料的冲击性能。     

掺镁碳酸熔盐液体导热特性

为克服碳酸熔盐热导率较低的不足,提出通过向三元碳酸熔盐（Li₂CO₃-Na₂CO₃-K₂CO₃）掺杂金属镁粉来改善导热性能的新思路,采用静态熔融法制备了掺杂1%、2%掺镁碳酸熔盐复合材料。采用扫描电镜-X射线能谱、阿基米德法、差示扫描量热法（DIN比热测试标准）和激光闪光法,分别观察了掺镁碳酸熔盐形貌结构,测量了熔盐和复合熔盐液体的密度、比热容、热扩散系数,最后计算获得复合熔盐液体的热导率。研究结果表明,镁粉的加入改变了纯盐（三元碳酸熔盐）的形貌结构,熔体内形成大量的2~5 μm球体颗粒,与纯盐相比,1%掺镁碳酸熔盐液体密度、热扩散系数和热导率都得到增强,液体比热容减小,复合熔盐液体的平均热导率增加了21.67%;2%掺镁碳酸熔盐液体密度、热扩散系数和热导率同样得到增强,虽然复合熔盐液体的比热容减小,但其平均热导率仍然增加了19.07%。1%掺镁碳酸熔盐具有更高的液体密度、热扩散系数和热导率,可作为传热介质在太阳能热发电传蓄热系统推广。     

CPA方程计算醇、水的比热容性质

针对立方型附加缔合项(CPA)状态方程(EoS)对比热容的计算精度不高的问题,采用11种包含不同性质的参数计算方法研究了CPA方程对极性缔合流体甲醇、乙醇、水比热容的计算精度。计算结果表明：不考虑比热容时,CPA方程的参数计算必须考虑蒸汽压性质,且蒸汽压计算精度越高,方程对液相比热容的预测精度越高;在参数计算中加入比热容后,CPA方程无法同时准确描述所有比热容性质,其中对液相比定压热容的计算精度最高;在参数计算过程中比热容性质只考虑液相比定压热容时,方程对蒸汽压、各相密度及液相比定压热容的平均绝对相对偏差都在3%及以内。     

Cu含量对高温相变材料Al-Cu合金热特性的影响

高温相变材料Al-Cu合金是蓄热性能最好的太阳能储存材料之一,而Cu含量对其热特性影响的相关研究未见报道。采用差示扫描量热法(DSC)和激光脉冲法(LFA)研究了Cu含量在7.4%~51.7%范围内的Al-Cu合金相变材料的相变温度、相变潜热、比热容、热扩散系数和热导率,并结合其金相组织对热力学性能变化规律的内在机理进行了分析。结果显示,当Cu含量在7.4%~51.7%范围内时,Al-Cu合金的相变温度在524.4~645.9℃范围内;随Cu含量的增加,Al-Cu合金的质量潜热呈递减趋势,而体积潜热却呈上升趋势。Al-7.4%Cu在熔化和凝固过程具有最大的质量潜热,分别为339.6、343.5 kJ·kg~(-1)。Al-51.7%Cu在熔化和凝固过程具有最大的体积潜热,分别为1179、1143 MJ·m~(-3)。当Cu含量在7.4%~51.7%范围内时,Al-Cu合金的比热容随Cu含量的增加呈递减趋势;当温度在25~500℃范围内时,Al-Cu合金的比热容随温度升高呈递增趋势。Al-7.4%Cu的比热容在25℃时为0.85 J·g~(-1)·K~(-1),在500℃时达到最高值1.08 J·g~(-1)·K~(-1)。此外,Al-Cu合金的热导率随Cu含量的升高而降低,但即使Cu含量达到51.7%,其常温下的热导率仍然高达104 W·m~(-1)·K~(-1)。综合研究结果表明,Al-Cu合金作为高温相变材料具有在太阳能蓄热领域中应用的巨大潜力。     

Thermal conductivity of binary ceramic composites made of insulating and conducting materials comprising full composition range – Applied to yttria partially stabilized zirconia and molybdenum disilicide

The thermal diffusivity and conductivity of dense and porous binary composites having an insulating and conducting phase were studied across its entire composition range. Experimental evaluation has been performed with MoSi₂ particles embedded into yttria partially stabilized zirconia (YPSZ) as prepared by spark plasma sintering (SPS). The thermal diffusivity of the composites was measured with Flash Thermography (FT) and Laser Flash Analysis (LFA) techniques. Subsequently, the thermal conductivity was determined with the measured heat capacity and density of the composites. The actual volume fraction of the conducting phase of the composites was determined with image analysis of X-ray maps recorded with scanning electron microscopy (SEM). The phases present and their density were determined with X-ray diffractometry (XRD) using Rietveld refinement. The thermal diffusivity increases with increasing volume fraction of MoSi₂. Porosity reduces the thermal diffusivity, but the effect diminishes with high volume fractions MoSi₂. The thermal diffusivity as a function of the MoSi₂ volume fraction of the YPSZ composites is captured by modelling, which includes the porosity effect and the high conductivity paths due to the percolation of the conductive phase.     

激光闪射法测量耐火材料的热物理性能

介绍了应用激光闪射法测量耐火材料比热容、热扩散系数以及导热系数等热物理性能的原理,列举应用实例说明了测试方法,并且讨论了影响实验数据准确性的因素。     

稠油比热容导热系数及粘温物性参数变化研究

利用Anton Paar MCR301旋转流变仪开展了不同区块稠油粘温性的实验研究,在20～300℃,利用HA-Ⅱ型比热容测定装置及HA-Ⅱ型导热测定装置,测定了岩石、水和不同区块稠油的比热容及不同区块稠油的导热系数.研究结果表明,稠油的粘度对温度非常敏感,随温度升高而大幅度降低.在20～300℃,稠油的比热容值在1.6840～4.4939 J/(g·K)变化,变化范围较大.稠油的导热系数都有随着温度的升高而降低的规律,并且在数值上较为接近,在20～300℃,导热系数在0.1196～0.1650W/(m·K)变化,变化范围很小.     

Cu含量对高温相变材料Al-Cu合金热特性的影响

高温相变材料Al-Cu合金是蓄热性能最好的太阳能储存材料之一,而Cu含量对其热特性影响的相关研究未见报道。采用差示扫描量热法（DSC）和激光脉冲法（LFA）研究了Cu含量在7.4%~51.7%范围内的Al-Cu合金相变材料的相变温度、相变潜热、比热容、热扩散系数和热导率,并结合其金相组织对热力学性能变化规律的内在机理进行了分析。结果显示,当Cu含量在7.4%~51.7%范围内时,Al-Cu合金的相变温度在524.4~645.9℃范围内;随Cu含量的增加,Al-Cu合金的质量潜热呈递减趋势,而体积潜热却呈上升趋势。Al-7.4% Cu在熔化和凝固过程具有最大的质量潜热,分别为339.6、343.5 kJ·kg^-1。Al-51.7% Cu在熔化和凝固过程具有最大的体积潜热,分别为1179、1143 MJ·m^-3。当Cu含量在7.4%~51.7%范围内时,Al-Cu合金的比热容随Cu含量的增加呈递减趋势;当温度在25~500℃范围内时,Al-Cu合金的比热容随温度升高呈递增趋势。Al-7.4% Cu的比热容在25℃时为0.85 J·g^-1·K^-1,在500℃时达到最高值1.08 J·g^-1·K^-1。此外,Al-Cu合金的热导率随Cu含量的升高而降低,但即使Cu含量达到51.7%,其常温下的热导率仍然高达104 W·m^-1·K^-1。综合研究结果表明,Al-Cu合金作为高温相变材料具有在太阳能蓄热领域中应用的巨大潜力。     

橡胶热传导性能的测定

介绍橡胶热传导性能测定的基本原理及导热系数,热扩散系数和比热容的测量方法。     

聚苯乙烯-二氧化硅@十四烷复合纳米相变胶囊的表征及其乳液性能

采用细乳液原位聚合法,研制了以正十四烷(Tet)为芯材、高热导率二氧化硅(SiO₂)改性的聚苯乙烯(PS)为壳层的新型复合纳米相变胶囊蓄冷材料;对复合胶囊形貌、组成以及热物性进行纳米粒度、透射电镜(TEM)、X射线光电子能谱(XPS)、差示扫描量热(DSC)以及热失重(TG)等表征,并测试其乳液的热导率、比热容、黏度及机械稳定性。结果显示:复合相变胶囊平均粒径为64.90 nm,具有规整的球形核壳结构,表面硅含量(质量分数)为3.27%,相变潜热达83.38 J·g^-1,复合壳材对芯材有很好的保护作用;其乳液的热导率及比热容峰值均优于未用SiO₂改性的纳米胶囊乳液,且乳液具有较高机械稳定性和较低黏度,可作为潜在的蓄冷用功能热流体。     

How phase (α and γ) and porosity affect specific heat capacity and thermal conductivity of thermal storage alumina

Ceramic materials are a potential medium to store thermal energy with a reasonable cost. Respective thermodynamic properties of ceramics generally depend on temperature, and the energy storage capacity significantly varies with microstructure and porosity of ceramics. In order to improve understanding on the correlation between microstructure change and energy storage capacity, two commercial grades of alumina specimens are characterized. Their thermo-mechanical properties are measured and correlated with temperature-dependent material phases (ie, α and γ phases) and porosity. Higher values of the γ phase fraction and the porosity result in a lower mass-based specific heat capacity when the temperature changes from room temperature to 1200°C. On the other hand, lower values of the γ phase fraction and the porosity lead to higher values of thermal conductivity and diffusivity between room temperature and 900°C. While both alumina specimens exhibit a decrease in specific heat capacity with increasing temperature for temperatures above 590°C, largely due to the phase transformation from γ to α, they both exhibit a decrease in thermal conductivity with increasing temperature in the same range. Generally a sample with a higher fraction of α phase and a lower porosity possesses a higher thermal conductivity. Quantitative relations are derived from experimental data.     

Influence of solution-precursor plasma spray (SPPS) processing parameters on the mechanical and thermodynamic properties of 8 YSZ

8?mol% yttria stabilized zirconia (8YSZ) coatings are prepared by solution precursor plasma spray (SPPS) technique under different spray conditions. Phase analysis is performed using X-ray diffraction (XRD) and Electron back scattered diffraction (EBSD) techniques. Irrespective of the processing conditions and the heat treatment temperatures, all samples displayed cubic and tetragonal zirconia phases. Vertical and horizontal cracks appeared in the microstructural analysis of the coatings. Coating prepared under spray conditions having 40?mm distance between the spray gun and the sample exhibit high hardness, both at 0?h and 10?h heat treatment holding time. To explore the suitability of the coatings for the heat insulating applications, the thermal diffusivity and thermal conductivity are calculated. The coating with 42?mm distance between the spray gun and the sample displayed lowest thermal conductivity from 400 to 1200?℃.     

Measurements of the thermal conductivity and thermal diffusivity of polymers

In this paper, the thermal conductivity and thermal diffusivity of nine polymers were measured by using the transient short‐hot‐wire method. The corresponding specific heat was measured with a commercial Differential Scanning Calorimeter (DSC). The effects of temperature on the thermal conductivity, thermal diffusivity, and the product of density and specific heat are further discussed. The results show that the transient short‐hot‐wire method can be used to measure the thermal conductivity, thermal diffusivity, and the product of density and specific heat of polymers within uncertainties of 3%, 6%, and 9%, respectively.