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91.
In this paper, the effect of wall conduction of an autothermal tubular methane microreformer is investigated numerically. It is found that the axial wall conduction can strongly influence the performance of the microreactor and should not be neglected without a careful a priori investigation of its impact. By increasing the wall thermal conductivity, the maximum wall surface temperature is decreased. Due to the complex exothermic–endothermic nature of the chemistry of reforming, the axial variation of the wall temperature is not monotonic. Methane conversion and hydrogen yield are strongly dependent on the wall inner surface temperature, hence the heat conduction through the channel wall. The equivalence ratio and the wall thickness also significantly affect the reforming effectiveness and must be carefully considered in reactor optimization. Furthermore, it is found that exothermic oxidation reaction mechanisms, especially partial oxidation, are responsible for syngas (hydrogen and carbon monoxide) production near the inlet. Farther downstream, in the oxygen deficient region, endothermic steam reforming is the main hydrogen producing mechanism. By increasing the thermal conductivity, steam reforming becomes stronger and partial oxidation becomes weaker. For all investigated inlet conditions, the highest hydrogen yield is obtained for no or very low conductive walls. 相似文献
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The rheological behaviors of high‐impact polystyrene (HIPS) and HIPS/TiO2 composites were investigated by use of a rheometer in the present article. HIPS exhibited a constant critical stress of the sharkskin in various temperatures, and the analysis indicated that the mechanism of sharkskin of HIPS was wall–slip and its special temperature dependency was determined by weak wall–melt adsorption. The experimental results also showed that the introduction of TiO2 into HIPS only slightly influenced the apparent viscosity (ηa) of the composites. Moreover, TiO2 exhibited an unusual effect on the non‐Newtonian index of the composites at high shear rate. Both phenomena indicated the increase of inner free volume induced by TiO2 in molecularly rigid HIPS. Moreover, it was noteworthy that a featured stress could be used to label the dispersion of TiO2 in the HIPS matrix, and the numeric affinity of this featured stress and the critical stress of sharkskin revealed that both processes were relevant to the same molecular relaxation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 802–807, 2005 相似文献
94.
热导率和热扩散率是天然气水合物资源开采关键性基础热物性数据,采用反应釜内壁衬有氟塑料材料,低过冷度,让水合物在反应釜内逐层生成的合成方法,获得可直接用于导热测试的二氧化碳水合物样品。采用瞬变平面热源法原位测试了温度264.68~282.04 K、压力1.5~3 MPa二氧化碳水合物热导率、热扩散率,并测试了二氧化碳水合物在268.05 K、0.6 MPa左右发生自保护效应过程中热导率、热扩散率,获得了晶态下和自保护效应过程中的二氧化碳水合物热导率、热扩散率变化特性。测试结果将为天然气水合物资源的开发利用提供基础数据和理论依据。 相似文献
95.
本文以现代控制理论为基础,引用线性控制系统的空间状态表达式来描述和探讨单个边界条件的确定问题。采用现有较为完善的空间离散方法-有限单元法或有限差分法,通过数值计算以获得较为准确的解。最后,由数值实验的例子来表明所采用方法的合理性和可靠性。 相似文献
96.
针对大型软包锂离子电池热物性参数的测定问题,提出适用于该型电池的热参数表征方法. 基于准稳态导热原理,建立电池的传热理论模型. 开展实验研究电池的比定压热容和导热系数与温度的依变关系,分析热损对测试结果的影响,对测试方法的有效性进行验证. 结果表明,电池比定压热容随着温度的升高而线性增大,导热系数受温度的影响较小. 在900 s内可以测得电池热参数在10~60 °C下的变化状况,实验验证结果显示测算精度高于92.3%,具有测算周期短、准确度高和测试灵活等优势. 相似文献
97.
燃气管线动态泄漏扩散的危险性分析 总被引:1,自引:0,他引:1
张甫仁 《土木与环境工程学报》2007,29(2):103-109
通过对燃气管线动态泄漏过程的分析,建立了动态泄漏率计算模型。以湍流扩散微分方程为基础,根据动态泄漏率不定常的特点,建立了燃气管线动态泄漏扩散模型。讨论分析了火灾爆炸的可能性危险范围和伤害性危险范围的参考标准和计算方法。在实际应用的基础上,对各种危险范围给予了讨论和分析,并对给定条件下的伤害及破坏范围给予了计算。这将为设立和制订高压长输管线和城市主要输运管道附近的重要建筑物(学校等)的修建安全距离提供安全标准和参考,同时也为降低事故可能造成的危害程度提供保障。 相似文献
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100.
2,7‐Di‐tert‐butylpyrene was oxidized to 2,7‐di‐tert‐butylpyrene‐4,5,9,10‐tetraone. The latter through condensation reaction with vicinal diamine such as diaminomaleodinitrile afforded heterocyclic monomer, 2,7‐di‐tert‐butyl pyrene[4,5][9,10]bis(2,3‐pyrazine‐5,6‐dinitrile), which was cyclotetramerized to the corresponding 2H‐ and metal‐pyrazinoporphyrazine‐based network polymers (2H‐PyzPz and M‐PyzPz, M = Co, Ni, Zn, or Cu). Elemental analytical results, Infrared, and NMR spectral data of the new prepared molecules are consistent with their assigned formulations. Molecular masses and metal contents of the synthesized polymers proved to be of high molecular masses, which confirm the efficiency of tetramerization polymerization and complexation reactions. Dielectric permittivity, ε′, loss tangent, tan δ, and ac conductivity, σac(ω), of 2H‐PyzPz and M‐PyzPz films were studied as a function of temperature and frequency. It was found that dielectric permittivity, ε′, decreases with the increase of frequency and increases with the increase in temperature. Ac conductivity, σac(ω), is found to vary as Bωs and the frequency exponent, s, is less than unity around room temperature indicating a dominant hopping process. On the other hand, σac(T) of all samples is thermally activated with low activation energies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011. 相似文献