共查询到20条相似文献，搜索用时 15 毫秒
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《Ceramics International》2020,46(11):19241-19247
A high temperature stable ceramic photonic structure is demonstrated with low thermal conductivity and suppressed external radiative heat transfer. The structure is based on a disordered arrangement of yttria-stabilized zirconia (YSZ) microparticles, called photonic glass (PhG). The prepared YSZ-PhG film exhibits low thermal conductivity of 0.03 Wm−1K−1 comparable to that of the air. The small point contacts of the adjacent YSZ particles are the main cause of such low thermal conductivity. After annealing at 1400 °C for 5 h, the solid thermal conductivity increased to 0.3 Wm−1K−1 at room temperature due to the thermally induced neck formation, associated with an increased contact area between adjacent particles. This thermal conductivity is still much lower than that of conventional YSZ thermal barrier coatings (TBCs) with approximately 1 Wm−1K−1. At the same time, the PhG structure is an efficient scatterer for thermal radiation in the wavelength range between 1 and 6 μm. In an only 100 μm thick structure an average reflection of 84% was obtained. At 1400 °C, the effective thermal conductivity is 0.2 Wm−1K−1. The presented structure is applicable to other oxides with even lower bulk thermal conductivity and can be considered for future TBCs. 相似文献
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Jian He Hangyuan Zhao Xiaolei Li Dong Su Huiming Ji Huijun Yu Zhipeng Hu 《Ceramics International》2018,44(8):8742-8748
The large-scale fibrous/aerogels composites are prepared by using zirconia fibrofelt (ZFF) as skeleton to give high strength and ZrO2-SiO2 aerogels (ZSA) as filler to give excellent thermal insulation through vacuum impregnation. The ZFF/ZSA with a low density of 0.302?g/cm3 and a high porosity (89%) exhibits large size of 180?mm in length, 180?mm in width and 25?mm in height which is larger than other fibrous aerogels. Meanwhile, the ZFF/ZSA exhibits high compressive strength of up to 0.17?MPa which is approximately six times higher than that of ZFF (0.028?MPa). The ZFF/ZSA shows a much lower thermal conductivity of 0.0341?W?m?1 K?1 at room temperature and 0.0460–0.096?m?1 K?1 during 500?°C and 1100?°C which are lower than that of conventional fibrous materials, indicating its excellent thermal insulation property in a wide temperature range, and the thermal insulation mechanism is analyzed. Thus, the large-scale, low density, high strength, and low thermal conductivity of ZFF/ZSA composites show enormous potential application in the fields of architecture, engineering pipes and aerospace for thermal insulation and protection. 相似文献
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《Journal of the European Ceramic Society》2022,42(15):7196-7202
Unidirectionally oriented architectures demonstrate a notable efficiency in enhancing the properties of macro-porous materials, yet are difficult to construct in a time- and cost-effective fashion. Here a facile approach was exploited for fabricating oriented macro-porous ceramic materials by employing natural graphite flakes as a fugitive material and preferentially aligning the flakes within ceramic matrices using accumulative rolling technique. Flaky to near-ellipsoid shaped pores with a homogeneous distribution were created in macro-porous zirconia ceramics with their porosity and microstructural characteristics adjustable by controlling the additive amounts of graphite flakes. The resulting materials exhibited a good combination of properties with high compressive strength up to over 1.5 GPa, which exceeds those of most other porous zirconia ceramics with similar porosities, along with low thermal conductivity of 0.92–1.85 Wm?1·K?1. This study offers a simple means for developing new oriented macro-porous materials with enhanced properties, and may promote their application by allowing for easy mass production. 相似文献
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The simulation of the firebox and the cracking coils of an olefin production unit is based on a zone model, discretizing the firebox and the external skin of the coils. The temperature distributions in the furnace and along the coil wall are generated simultaneously with the temperature, conversion and pressure profiles inside the cracking coils. Important temperature variations in the firebox are revealed. The program is used to investigate the influence of the firing pattern on the temperatures and on the product distribution 相似文献
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Three methods of estimating the effective emissivity of a gas-particle suspension are compared and the radiative heat transfer coefficient of an isothermal suspension is defined. Heat flux measurements obtained from circulating fluidized bed combustors are examined. Radiation from a particle suspension with core temperature dominates the radiative heat transfer in the upper part of the furnace, where the particle density is low and no substantial particle boundary layers are formed. Over the lower parts of the heat transfer surfaces, where significant thermal and particle boundary layers are present, the radiative heat flux is dominated by emission from the relatively low temperature particle layer in the vicinity of the heat receiving surface. 相似文献
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针对广州乙烯装置裂解炉拱顶保温失效的问题进行分析并根据失效的原因，提出改造和修复措施，在实际生产中证实该措施实用、有效确保裂解炉的“安稳长满优”运行。 相似文献
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《Journal of the European Ceramic Society》2020,40(5):2090-2096
Mullite fibrous porous ceramics is one of the most commonly used high temperature insulation materials. However, how to improve the strength of the mullite fibrous porous ceramics dramatically under the premise of no sacrificing the low sample density has always been a difficult scientific problem. In this study, the strategy of using mullite nanofibers to replace the mullite micron-fibers was proposed to fabricate the mullite nanofibrous porous ceramics by the gel-casting method. Results show that mullite nanofibrous porous ceramics present a much higher compressive strength (0.837 MPa) than that of mullite micron-fibrous porous ceramics (0.515 MPa) even when the density of the mullite nanofibrous porous ceramics (0.202 g/cm3) is only around three quarters of that of the mullite micron-fibrous porous ceramics (0.266 g/cm3). The obtained materials that present the best combination of mechanical and thermal properties can be regarded as potential high-temperature thermal insulators in various thermal protection systems. 相似文献
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《Journal of the European Ceramic Society》2022,42(15):7209-7218
How to improve the strength of fibrous porous ceramics dramatically under the premise of no sacrificing its low density and thermal conductivity has remained a challenge in the high-temperature thermal insulation field. In this paper, a new kind of high-strength mullite fiber-based ceramics composed of interlocked porous mullite fibers was prepared by nanoemulsion electrospinning and dry pressing method. Results show that as to the porous ceramics with the same density (～ 0.8 g/cm3), the three-dimensional skeleton structure composed of porous mullite fibers was much denser than that composed of solid mullite fibers. Therefore, porous mullite fiber-based ceramics exhibited a higher compressive strength (5.53 MPa) than that of solid mullite fiber-based ceramics (3.21 MPa). In addition, porous mullite fiber-based ceramics exhibited a superior high-temperature heat insulation property because the porous structure in fibers could reduce the radiant heat conduction. This work provides new insight into the development of high-temperature thermal insulators. 相似文献
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《Ceramics International》2022,48(20):29913-29918
Ceramic fiber felts are attractive candidates for high temperature insulation due to their lightweight, high porosity and low thermal conductivity. In this work, ceramic felts constructed by γ-Y2Si2O7 fibers were prepared by a facile method of Y–Si–O/PVB sol-gel electrospinning combined with subsequent high-temperature calcination. Effects of calcination temperature on the phase composition, microstructure and thermal insulation properties of ceramic felts were systematically studied. Results indicated that the organic components in the sol-gel fibers were removed after high temperature calcination, while the fibers kept the original continuous microtopography with high aspect ratios. Ceramic fiber felts of pure γ-Y2Si2O7 phase could be obtained after calcinated at 1300 °C. The as-prepared paper-like γ-Y2Si2O7 fiber felt presented low density of ～120 mg/cm3 and a high porosity up to 97.03%. Combined with the inherent high temperature stability and low thermal conductivity of γ-Y2Si2O7, this light ceramic felts possessed high-temperature resistance and thermal insulating property (low thermal conductivity of 0.052 W m?1 K?1). The successful preparation of this ceramic fiber felt may provide a perspective for insulation materials used in harsh environments. 相似文献
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An emitting, absorbing, and anisotropically scattering plain medium containing a suspension of ZnO particles is considered, in which the particles are directly exposed to high-flux irradiation and undergo shrinkage during their endothermic dissociation into Zn(g) and O2 at above 2100 K. The unsteady energy equation that links the rate of radiative heat transfer to the rate of the chemical reaction is formulated and solved numerically by the finite volume technique and the explicit Euler time-integration scheme. The path-length Monte Carlo method is applied for modeling the radiative transfer within the suspension using the absorption/scattering coefficients and the scattering phase function obtained from the Mie theory. It is found that the particle suspension can be heated rapidly from its initial 300 K to over 1800 K in less than 0.1 s, resulting in a more uniform temperature profile as the reaction progresses, particles shrink, and the suspension becomes optically thinner. The chemical conversion increases with decreasing initial particle diameter and volume fraction due to the efficient radiative absorption. 相似文献
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《Journal of the European Ceramic Society》2022,42(13):5995-6004
Ceramic nanofiber aerogel is one of the most attractive insulation materials in recent years. However, its practical application ability is limited at high temperature due to high radiation heat transfer. Herein, we constructed a novel closed-cell/nanowire structured mullite-based nanofiber composite aerogel via electrospinning technology and solvothermal synthesis method. Hollow TiO2 spheres were used as pore-making material and infrared opacifier to reduce fiber solid heat conduction and high temperature radiation heat transfer simultaneously. In addition, TiO2 nanowires grown in-situ on the fiber surface further decrease the radiation heat transfer of aerogel and improve the mechanical properties. The unique structure endows the aerogel with high mechanical robustness (0.32–0.35 MPa, 10% strain), low density (39.2–47.5 mg/cm3) and ultralow thermal conductivity (~0.017 W m?1 K?1 at 25 ℃ and ~0.056 W m?1 K?1 at 1000 ℃). This work offers a novel strategy for the development of ceramic nanofiber aerogel at high temperature. 相似文献
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《Ceramics International》2022,48(24):36287-36296
Multifunctional aerogels with high porosity and good thermal insulation have attracted much attention in the field of energy and aerospace engineering. In this work, a three-dimensional BN fiber aerogel with hierarchically porous structure was prepared through a freeze-drying combined with in-situ carbothermal reduction nitridation route. The synthesized BN fiber aerogel exhibits a specific surface area of 154.3 m2/g, a high porosity of 96.8% and hydrophobicity. Moreover, the BN fiber aerogel shows a low thermal conductivity of 0.051 W/(m·K) and excellent thermal insulation properties owing to its hierarchical porous structure. Particularly, the BN fiber aerogel still maintains its low thermal conductivity and a rather high mechanical strength after re-heated at 1473 K for 3 h in Ar atmosphere, suggesting excellent high-temperature service performance. The successfully developed multifunctional BN fiber aerogel holds promising potential in high-temperature thermal insulation fields. 相似文献
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《Ceramics International》2016,42(6):7216-7222
Silica cryogel-glass fiber composites with a high specific surface area and high mesoporosity were fabricated via a simple still original drying technique. By applying vacuum at ambient temperature, the system evolution has been monitored and represented in the water phase diagram. The ratio of solvent/silica loading significantly affected the porous structure and thermal insulating properties of the blanket. From the results of BET surface area, apparent density and porosity studies, the microstructures and specific surface areas of the composites were greatly affected by changing the silica amount in the sol. The microstructure of silica cryogel blanket exhibits a porous structure consisting of glass fibers of diameter ~7 μm interconnected with solid silica clusters (5–20 μm). Silica cryogel-glass fiber blankets with low densities from 0.13–0.24 g/cm3 and thermal conductivity as low as 0.02–0.035 W/mK were obtained using this cost effective, hazardous free and time saving method. The pH of the silica sol influenced the gelling property and the thermal conductivity of the composites. 相似文献
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建立了蒸汽管道多层复合保温结构传热模型,采用DN200mm管道实验研究了不同保温结构和保温材料对隔热性能的影响,根据实验数据验证了数学模型准确性,并以此为基础给出了不同工况下最佳保温方案的确定方法。实验结果显示,管道表面热流密度随着对流层的加入和气囊层数的增加而降低,随披肩厚度和保温总厚度的增加逐渐降低,而反射层数量增加热流密度先降低后升高。传热模型预测结果与实验数据高度吻合,相差不到6%。从经济性分析,不宜采用对流层作为保温材料。最终确定的最佳保温方案能够显著降低系统的供热总成本,最优保温厚度值随管内介质温度和管径的增加而升高。对于温度大于400℃的高温管道,采用复合保温结构相比于单一硅酸铝保温可节省超过30%的投资。 相似文献
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A mathematical heat transfer model for a silica aerogel-based thermal insulation coating was developed. The model can estimate the thermal conductivity of a two-component (binder-aerogel) coating with potential binder intrusion into the nano-porous aerogel structure. The latter is modelled using a so-called core–shell structure representation. Data from several previous experimental investigations with silica aerogels in various binder matrices were used for model validation. For some relevant cases with binder intrusion, it was possible to obtain a very good agreement between simulations and experimental data with shell thickness and/or thermal conductivity of the shell as adjustable parameters. However, the experimental data was not sufficiently detailed to allow a separation of the effects of the two parameters. In the ideal case of no aerogel binder intrusion, a comparison with a coating containing intact hollow glass or polymer spheres showed that silica aerogel particles are more efficient in an insulation coating than hollow spheres. In a practical (non-ideal) comparison, the ranking most likely cannot be generalized. A parameter study demonstrates how the model can be used, qualitatively, to get an indication of the effect of important model parameters on the thermal conductivity of an insulation coating. With relevant data available for service life exposure conditions and raw material costs, the model can also be used as an optimization algorithm. 相似文献