基于热探针的建筑用复合相变材料的导热系数的测定

针对建筑用有机相变材料导热系数较低的缺点,通过实验研究了添加石墨增强相变材料导热系数的方法。选择癸酸-十六醇低共熔混合物相变材料作为蓄热介质,通过热探针法对其导热系数的测定,得到其导热系数的变化规律。对添加不同比例石墨的粉煤灰相变材料与纯粉煤灰相变材料的导热系数用热探针法进行对比试验,并在实验条件下找出石墨的最佳比例。实验数据表明:与不添加石墨的粉煤灰相变材料相比,添加石墨添加剂的粉煤灰相变材料的导热系数得到显著提高,换热性能得到增强,添加石墨的最佳比例是10%.     

膨胀石墨/芒硝复合定形相变材料制备及性能研究

以复合芒硝(SCNa)为相变材料,膨胀石墨为载体,采用真空吸附法制备出导热增强型膨胀石墨/复合Na_2SO_4·10H_2O定形相变材料。试验结果表明:表面活性剂OP-10(质量分数5%)的加入能有效提高膨胀石墨和复合Na_2SO_4·10H_2O相变材料的结合稳定性,表面活性剂的添加对定形相变材料导热系数基本无影响,添加表面活性剂的膨胀石墨定形相变材料导热系数为2.26 W/(m·K),为原复合芒硝相变材料的215%。     

利用纳米石墨强化正癸酸-十四醇复合相变材料的导热性能

作为常用的有机相变材料,脂肪酸具有循环熔融/结晶稳定的热性能以及无毒、无腐蚀性等优点,但脂肪酸体系的导热系数(0. 1～0. 3 W·m~(-1)·K~(-1))低,限制了它的工业应用范围。为了提高正癸酸(CA)-十四醇(TA)复合相变材料的导热性能,本实验选用CA与TA物质的量比为7∶3的复合相变材料为基液,通过添加不同质量分数的纳米石墨制备出正癸酸-十四醇/纳米石墨复合相变材料体系。研究发现,当添加纳米石墨的质量分数为0. 1%～0. 9%时,能形成较为稳定的悬浮液。通过SEM、DSC和Hot Disk导热系数测定仪对复合材料的主要热物理性能进行表征,分析结果表明,正癸酸-十四醇/纳米石墨复合相变材料的导热系数相对原基液有较大幅度的提高,而相变潜热和相变温度没有太大变化。当添加纳米石墨的质量分数为0. 6%时,所制备的正癸酸-十四醇/纳米石墨复合相变材料的综合性能最佳,其固态和液态导热系数分别提高了39. 5%、35. 2%,相变温度和相变潜热分别为20. 42℃、154. 25 k J/kg,并且具有良好的热稳定性。     

膨胀石墨/石蜡相变复合材料有效导热系数的数值计算

通过膨胀石墨粉与石蜡混合制备相变复合材料可有效提高该储能材料的传热性能。为研究膨胀石墨/石蜡相变复合材料的导热机制,提出了膨胀石墨粉与石蜡混合后的3尺度层次固体有效导热系数计算方法。然后,通过数值模拟计算得到了具有不同体积分数和不同导热系数的膨胀石墨导热颗粒的膨胀石墨/石蜡相变复合材料的有效导热系数。结果表明:膨胀石墨能够有效地提高石蜡的导热性能,当膨胀石墨的体积分数为10%时,膨胀石墨/石蜡相变复合材料的有效导热系数是纯石蜡的9倍。此外,提高底层尺度的石墨片与石蜡的混合程度及降低底层尺度石墨的体积分数都能有效提高膨胀石墨/石蜡相变复合材料的有效导热系数。所得结论为探究膨胀石墨粉提高相变复合材料导热系数的机理奠定了基础。     

石墨泡沫/共晶盐复合相变材料的制备及其热物性

为强化二元硝酸共晶盐(NaNO3/KNO3)的导热性能,在共晶盐中添加石墨泡沫制出石墨泡沫/共晶盐复合相变材料;对共晶盐和复合相变材料的相变特性进行差示热分析;对石墨泡沫的导热系数和复合相变材料的有效导热系数进行测定,并用拉曼光谱对复合相变材料进行稳定性分析。结果表明,石墨基复合材料可以用熔融浸渗法制备,且制备样品的稳定性能良好。复合相变材料的相变温度(221.3°C)与共晶盐(222.4°C)相似,其相变潜热与基于复合材料中共晶盐含量的潜热值相近(下降3.74%)。受石墨骨架高热导率的影响,复合相变材料的导热能力明显提高,与纯共晶盐比增加了102倍。     

石墨/石蜡复合相变储热材料的热性能研究

膨胀石墨(EG)在超声作用下解离成微米级石墨片层(MSGF),并加入到石蜡基体中制备得到石墨/石蜡复合相变储热材料,并对复合相变材料的结构和热性能进行表征。实验结果表明,该石墨/石蜡复合相变储热材料储热速率加快,化学性质稳定。随MSGF质量分数的增加,固态及液态复合材料的导热系数均呈非线性显著增长,相变温度及相变潜热略有降低。     

膨胀石墨/LiCl-NaCl复合相变材料导热系数各向异性

用水溶液法制备了膨胀石墨/LiCl-NaCl复合相变储能材料,利用扫描电镜观测了试样的微观形貌,并且利用Hot-Disk热学常数分析仪测试了试样常温下的导热系数。实验结果表明,共晶盐能够被吸附到石墨片层之间,形成稳定、均一的复合相变材料;其导热系数随压力和石墨含量的增加而不断增大,并具有各向异性;成型压力和膨胀石墨掺量是影响其性质的两个重要因素,在一定范围内,其导热系数和各向异性随成型压力的增加而增大,压力超过一定范围,两者变化幅度减小;石墨掺量达不到一定比率时,其导热系数和各向异性变化不显著,当达到一定比率后,两者变化幅度增大;成型压力和膨胀石墨掺量对其导热系数的影响有耦合作用;通过取向度Φ给出了垂直压力和平行压力方向上的导热系数计算公式。     

己二酸/膨胀石墨复合相变材料性能研究

以己二酸为相变材料,膨胀石墨为导热增强相,采用机械混合与熔融吸附的方法,制备出己二酸/膨胀石墨复合相变储热材料。通过FT-IR、DSC、热常数分析仪、TG、FE-SEM及热循环实验对制备的复合材料进行了结构和性能研究。结果表明,膨胀石墨能够有效吸附己二酸,两者之间化学相容性良好;随着膨胀石墨掺量的增加,复合材料的相变潜热有减少趋势,导热系数则相应提高;当膨胀石墨的掺量为8%(质量分数)时,制备的复合材料的熔化、凝固相变潜热分别为237.66,220.49J/g,导热系数为2.99W/(m·K),具有良好的热稳定性。     

微纳米复合导热材料的制备及导热性能

采用超声处理方法将膨胀石墨剥离成微纳米石墨片,并以制备的微纳米石墨片为导热填料采用溶液共混法对聚偏氟乙烯(PVDF)进行改性,制备出微纳复合导热材料。通过扫描电子显微镜对其微观结构进行了表征,结果表明通过超声处理可以使膨胀石墨发生部分剥离得到微纳米石墨片。导热性能测试结果表明,复合材料的导热性能随着超声处理时间的增加而增加;当超声处理时间为150min时,复合导热材料的导热系数是膨胀石墨填充PVDF的1.8倍。     

石蜡-正辛酸/石墨相变材料的制备及热物性分析

目的 为了减少产品在运输过程中由于温度而造成的损坏,研发一种石蜡-正辛酸/石墨相变材料,并探究其性能.方法 主要通过热物性实验,包括差示扫描量热、TEMPOS热特性来分析石蜡-正辛酸/石墨相变材料的性能.结果 配置了6种不同质量比的石蜡和正辛酸,质量比为0.2:0.8的石蜡-正辛酸达到共晶点,相变潜能为161.31 J/g,相变温度为13.4℃;以质量比0.2:0.8的石蜡-正辛酸为原料,添加不同添加量的石墨来提高导热性能,发现当石墨质量分数为20％时,导热系数提高了3.9倍,且循环稳定性好.结论 从相变潜能、相变温度和导热系数等3个方面考虑,当质量分数为20％的石墨添加在质量比为0.2:0.8的石蜡-正辛酸相变材料中,可得最佳石蜡-正辛酸/石墨相变材料,满足10～20℃运输环境的要求.     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

卧式金属罐容量的测量结果不确定度

本文根据多年的实践检定经验 ,参照JJF1 0 59- 1 999《测量不确定度评定与表示》以及《测量不确定度表达 1 0讲》 ,对卧式金属罐容量的测量结果不确定度进行了评定。     

盐酸浓度不确定度的评估

通过对盐酸浓度标定的过程分析，找出影响结果的各个分量，进行不确定度的评定，按照计量技术规范给出标准的表示法。     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.