共查询到20条相似文献,搜索用时 125 毫秒
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根据砖组织中气孔的分布状况,研究了MgO-C砖组织与热导率的关系。采用水银压入法测定了气孔孔径分布,证实了气孔孔径分布与热导率有明确的关系。细小气孔量增多时,热导率呈下降趋势,这是细小气孔在砖组织中均匀分散,有效阻断石墨颗粒间的接触的缘故。通过组织模型对这种关系进行了解析。并制作了将气孔分为连续相和分散相的组织模型,验证了细小气孔在砖组织中均匀分散,阻断石墨颗粒间的接触时,其容积越大,热导率会越小,因此细小气孔的容积与热导率有密切关系。 相似文献
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高导热聚丙烯复合材料导热性能的研究 总被引:1,自引:0,他引:1
研究了石墨填充改性聚丙烯复合材料的流动性能、力学性能及其导热性能。实验结果表明,用热导率高、粒径小的石墨对聚丙烯进行填充改性,可以显著提高复合材料的热导率,当石墨质量百分含量为45%时,石墨/PP复合材料的热导率达到1.29W/(m·K),是纯聚丙烯树脂的6倍多;但流动性能和力学性能有所下降。同时发现热导率理论模型只能在低填充情况下适用。 相似文献
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用无压浸渗法制备了体积分数高达70%的碳化硅颗粒增强铝基复合材料,用SEM,XRD对试样进行了形貌和成分分析.测定了复合材料的热膨胀系数及热导率,并和理论模型进行了比较.结果表明:高体积分数SiC/Al复合材料的热膨胀系数为5.68×10-6/K,热导率为155 W/m·K,满足电子封装材料的要求. 相似文献
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一、前言热导率是确定陶瓷、耐火材料耐热冲击性能的重要参数,也是设计窑炉炉壁时选择材料的依据.热导率测定的方法有:稳定热流法的比较法和非稳定热流法的热线法等.自HAUPIN首先用热线法成功地测定出陶瓷的热导率之后,到七十年代,许多欧洲国家相继建议将热线法定为测定陶瓷、耐火材料的标 相似文献
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线形低密度聚乙烯/碳纤维复合材料的热导率 总被引:1,自引:0,他引:1
邵时雨;齐暑华;安群力 《中国塑料》2009,23(3):46-49
用模压方式制备了线形低密度聚乙烯(PE-LLD)/CF(CF)复合材料,研究了CF表面偶联剂处理、分散方式及含量对复合材料热导率的影响。结果表明,用偶联剂处理过的CF填充PE-LLD复合材料热导率提高。用超声分散法制备的试样热导率优于球磨混合法和熔融混炼法制备的试样。随着CF含量的增加,PE-LLD/CF复合材料热导率提高,同时保持了良好的力学性能。当CF含量为10 %(质量分数,下同)时,用超声分散法制备的复合材料热导率达1.4 W/(m·K),是纯PE-LLD的6倍多。 相似文献
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Marianne I. K. Collin David J. Rowcliffe 《Journal of the American Ceramic Society》2001,84(6):1334-1340
The thermal shock resistance (indentation–quench method), fracture toughness, and thermal conductivity of three alumina–silicon–carbide–whisker composites and alumina have been investigated. A new procedure for the evaluation of thermal conductivity data is suggested, and higher room-temperature thermal conductivity than that reported in the literature is determined for silicon carbide whiskers. The ranking of the materials according to thermal shock resistance is consistent with the ranking according to fracture toughness but disagrees with the ranking according to thermal conductivity. This finding supports the analytically obtained result that, in defining thermal shock resistance, fracture toughness is more important than thermal conductivity. 相似文献
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Thermal conductivity of the pyrolysis layer in the charring material is of great importance for the optimal design of thermal protection system (TPS) in reentry vehicles. A method based on the thermogravimetry data of the charring material is presented to predict the thermal conductivity of the pyrolysis layer and the distribution of thermal conductivity of the pyrolysis layer is estimated. In addition, in order to validate the accuracy of this method, thermal response of the charring material is calculated with the predicted thermal conductivity and compared with the experimental data. The simulation results agree with the measured data and the numerical results indicate that taking this method to calculate the thermal conductivity of the pyrolysis layer is more compatible with the actual situation. This study is helpful to the optimization of the TPS. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48346. 相似文献
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Xiaohui Zhao Meng Zhao Xiaorui Ren Yixin Zheng Yan Xing Jun Yang Min Wang Chunlei Wan Wei Pan 《Journal of the American Ceramic Society》2021,104(9):4788-4802
Air plasma sprayed yttria-stabilized zirconia thermal barrier coatings are widely applied in gas turbines and aviation engines, which usually contain multifarious and multiscale defects, such as pores, cracks, and amorphous layers. They all significantly lower the thermal conductivity of the coating but in drastically different ways depending on their morphologies and orientations. Establishing an accurate correlation between the microstructure and the thermal conductivity requires not only a precise separation and estimation of different kinds of defects but also a reasonable mathematic model to describe their effect on thermal conductivity. In this research, cross-section ion polishing and image analysis were chosen as a reliable assembly for characterizing multifarious defects of porous coatings, which was almost undamaged compared with the traditionally mechanical polishing. The effect of different microscale defects on the thermal conductivity was respectively and quantitatively studied to build a mathematical model. A thermal resistance induced by amorphous layers was introduced into the model, which was found to have a linear relationship with the amorphous layer concentration. It was also found a linear relationship between the amorphous layer concentration and the spraying times. The predicted thermal conductivity of porous coatings by multifarious-defect-concerned model fits the data measured using the steady heat flow method very well. This research confirms the applicability of image-analysis-based modeling as a simple, reliable, and versatile method for thermal conductivity prediction of porous coating systems. 相似文献
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Toru Shimizu Kazuhiro Matsuura Harumi Furue Kunio Matsuzak 《Journal of the European Ceramic Society》2013,33(15-16):3429-3435
Alumina has high heat resistance and corrosion resistance compared to other ceramics such as silica or mullite. However, for its application to refractory bricks, its high thermal conductivity must be reduced. To reduce this thermal conductivity by increasing the porosity, a GS (gelation of slurry) method that can produce high porosity solid foam was applied here to produce the alumina refractory brick. This method was successfully applied to produce alumina foam with high porosity and thermal conductivity of the foam is evaluated. At room temperature, the thermal conductivity was about 0.12 W/mK when the foam density was 0.1 g/cm3. At elevated temperature above 783 K, thermal conductivity of the foam was strongly affected by heat radiation and increased with increasing temperature, in contrast to the thermal conductivity of alumina itself, which decreased with increasing temperature. The alumina foams developed here achieved sufficient thermal insulating properties for use in refractory bricks. 相似文献
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This work reports the development of a methodology for the measurement of thermal conductivity of thermosetting polymers during their cure. The study addresses the reliability and robustness of the method through FEA modeling and testing using a noncuring material with known thermal conductivity. The thermal conductivity and its evolution during the cure has been measured for three widely used aerospace epoxy resins, namely, RTM6, 890RTM, and the XU3508/XB3473 system as function of cure temperature. A constitutive model expressing the dependence of thermal conductivity on the degree of cure and temperature has been established. The device developed here can measure thermal conductivity of epoxy resin with accuracy up to 3%. © 2018 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47015. 相似文献
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采用非平衡分子动力学方法模拟了三维石墨烯-碳纳米管复合结构的法向热导率。结果表明相比于多层石墨烯,其法向热导率提高了一个量级,其界面热阻相比碳纳米管的接触热阻降低了一个量级,但是石墨烯和碳纳米管的界面形变又阻碍了三维石墨烯-碳纳米管复合热导率的进一步提高。通过其振动态密度和重叠能进一步探究了三维石墨烯-碳纳米管复合结构结构能量的传递及声子的局域化情况。结果表明,碳管的添加激发了更多中高频声子振动参与传热,但是依然是低频声子占据主导;验证了界面处的形变是阻止法向热导率进一步提升的主要因素。 相似文献
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F. H. Norton 《Journal of the American Ceramic Society》1927,10(1):30-52
The problem of measuring the thermal conductivity of materials up to high temperatures has been studied, especially in regard to the sources of error. This investigation has shown that many of the previous determinations of thermal conductivity may have had little precision due to a lack of appreciation of the errors involved. The values of thermal conductivity for a number of refractories are given, as obtained by a new type of apparatus designed to eliminate to a considerable extent the errors of measurement. However, it is believed that these values may have an error as high as ± 25 % for the better heat conductors; so there is still much work to be done in developing a method for measuring thermal conductivity with the precision usual in other physical measurements. 相似文献
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This paper describes the preparation of fumed silica compacts for thermal insulation, using wet processing method. A series of thermal insulation compacts based on fumed silica powder and glass fibers were prepared. The influence of the mass ratio about fumed silica and glass fibers on the fracture strength and thermal conductivity was investigated. The results showed that the fracture strength increased first and then decreased with the mass ratio increasing. The thermal conductivity decreased linearly with the mass ratio increasing. When the compact was pressed under 6 MPa with a mass ratio of 5:1, it exhibited excellent thermal insulation at room temperature with a thermal conductivity of 0.042W/mK. Moreover, the compact was hydrophobic, after being modified by KH‐570. 相似文献
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This paper proposes a method for measuring the thermal conductivity of compressible powders, in particular of powders which do not permit a calculation of sphere models. The apparatus, which is briefly duscussed, is designed to compress powders hydrostatically up to 600 bars while measuring the thermal conductivity with a hot wire lance. With this range of compression it is possible to determine the thermal conductivity for almost every plastic powder, non-compressed powders as well as quasi-solid materials. Experimental results are given for polytetrafluorethylene (PTFE) and polyethylene (PE) powders. The effect of crystallization on thermodynamic properties of polyethylene under high pressure is discussed. 相似文献
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In this study, enhancements of thermal conductivities of ethylene glycol, water, and synthetic engine oil in the presence
of copper (Cu), copper oxide (CuO), and multi-walled carbon nanotube (MWNT) are investigated using both physical mixing method
(two-step method) and chemical reduction method (one-step method). The chemical reduction method is, however, used only for
nanofluid containing Cu nanoparticle in water. The thermal conductivities of the nanofluids are measured by a modified transient
hot wire method. Experimental results show that nanofluids with low concentration of Cu, CuO, or carbon nanotube (CNT) have
considerably higher thermal conductivity than identical base liquids. For CuO-ethylene glycol suspensions at 5 vol.%, MWNT-ethylene
glycol at 1 vol.%, MWNT-water at 1.5 vol.%, and MWNT-synthetic engine oil at 2 vol.%, thermal conductivity is enhanced by
22.4, 12.4, 17, and 30%, respectively. For Cu-water at 0.1 vol.%, thermal conductivity is increased by 23.8%. The thermal
conductivity improvement for CuO and CNT nanofluids is approximately linear with the volume fraction. On the other hand, a
strong dependence of thermal conductivity on the measured time is observed for Cu-water nanofluid. The system performance
of a 10-RT water chiller (air conditioner) subject to MWNT/water nanofluid is experimentally investigated. The system is tested
at the standard water chiller rating condition in the range of the flow rate from 60 to 140 L/min. In spite of the static
measurement of thermal conductivity of nanofluid shows only 1.3% increase at room temperature relative to the base fluid at
volume fraction of 0.001 (0.1 vol.%), it is observed that a 4.2% increase of cooling capacity and a small decrease of power
consumption about 0.8% occur for the nanofluid system at a flow rate of 100 L/min. This result clearly indicates that the
enhancement of cooling capacity is not just related to thermal conductivity alone. Dynamic effect, such as nanoparticle dispersion
may effectively augment the system performance. It is also found that the dynamic dispersion is comparatively effective at
lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime. Test results
show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid. 相似文献