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由以质量,动量和能量三大守恒定律为基础的湍流两相流理论出发,建立了描述气-固流化床内两相流动的数学模型,在微型计算机上编写了相应的数值计算和图形处理程序,为了验证模型的可靠性,本文着手模拟与分析了单组分颗粒体系两维射流流化床内气,固相速度场,空隙度和压力场随时间,空间变化规律;得到了与前人实验结果相吻合的结论。 相似文献
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研究了以粉体氧化铝水合物为固相的鼓泡浆液反应器的平均气含率和固体浓度分布特性。考察了表观气速、体系温度、静液高度、固相浓度及气体分布板的开孔率等对气含率的影响和不同性质氧化铝水合物在塔中的悬浮和轴向浓度分布情况。结果表明气速增大或开孔率较大时气含率增大,但固相浓度大小对气含率没有影响。水合氧化铝固体粉末在鼓泡塔中的浓度分布特性与固体的堆积密度和吸水性能有关,吸水率大堆积密度小的拟薄水铝石在低气速条件下就可完全均匀悬浮。以上结果为用气液固三相鼓泡反应器制备晶粒大小均匀的拟薄水铝石提供了可能性。 相似文献
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从湍流两相流理论出发,详细推导了描述气-固流化床内两相流动的双流体力学模型,根据方程的封闭性原理给出了所需构关系的表达式;针对模型方程的非线性,耦合性和形式相同等特点,集合气-固流化床内εg+εs=1及εs〈εs,max的限制,在数值计算上提出了改进的SIMPLE算法。在微型计算机上开发了CASICC软件包,其计算程度在NDP-Fortran环境下执行,可以给出了稳态或非稳态的二维直角坐标系或坐标 相似文献
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采用Monte Carlo方法重构了LiCoO2电池正极的三维微结构,重构单元的特征尺寸为几十纳米量级,从而得到了明确区分活性材料、固体添加物以及孔相(电解液)的微结构.通过对重构电极的特征化分析,得到了微结构中特定相的连通性和扭曲率、组分体积分数的空间分布、比表面积、孔径分布等特征信息.采用D3Q15格子Boltzmann模型(LBM)计算了该重构电极的有效热导率、电解液(或固相)的有效传输系数.同时发现,与随机行走方法以及Bruggemann关系式计算获得的扭曲率数值相比,LBM预测值更可靠. 相似文献
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研究了以粉体氧经铝水合物为固相的鼓泡浆液反应器的传热性能和温度分布及沸合特性。结果表明两相和三相体系的传热速度均随表观气速的增大而增大,固相的加入强化了体系的传热效果,但固体浓度大小无明显影响。 相似文献
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用超临界流体干燥法制备出大孔高比表面高分散态Fe/ZrO_2气凝胶超细粒子催化剂,研究了在其制备过程中织构性质、颗粒大小、体相和表面结构的变化,并与普通浸渍法制备的Fe/ZrO_2催化剂作了对比。对几种Fe/ZrO_2催化剂的F-T反应性能考察表明,Fe/ZeO_2气凝胶超细催化剂显示出高的反应活性;随载体ZrO_2颗粒尺寸减小,活性组分铁的分散度变大,其颗粒尺寸变小,催化剂比表面积增大,反应活性增大,甲烷和低碳烃生成量增加,重质组分减少,认为产物烃分布主要受催化剂活性相颗粒尺寸效应制约。 相似文献
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The variations of thermal conductivity with temperature for Pb–Sn alloys were measured using a radial heat flow apparatus. The variations of electrical conductivity with the temperature for same alloys were determined from the Wiedemann–Franz law by using the measured values of thermal conductivity. According to present experimental results, the thermal and electrical conductivity of Pb–Sn alloys linearly decrease with increasing temperature but exponentially increase with increasing the composition of Sn. The enthalpy of fusion and the change of specific heat for Pb–Sn alloys were also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from eutectic liquid to eutectic solid. 相似文献
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O. A. Almanza M. A. Rodríguez‐Prez J. A. De Saja 《Journal of Polymer Science.Polymer Physics》2000,38(7):993-1004
The thermal conductivity and the cellular structure as well as the matrix polymer morphology of a collection of chemically crosslinked low‐density closed cell polyolefin foams, manufactured by a high‐pressure nitrogen gas solution process, have been studied. With the aid of a useful theoretical model, the relative contribution of each heat‐transfer mechanism (conduction through the gas and solid phases and thermal radiation) has been evaluated. The thermal radiation can be calculated by using a theoretical model, which takes into account the dependence of this heat‐transfer mechanism with cell size, foam thickness, chemical composition, and matrix polymer morphology. A simple equation, which can be used to predict the thermal conductivity of a given material, is presented. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 993–1004, 2000 相似文献
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An experimental study of the thermal decomposition of powdered cellulose and pine sawdust has been performed. The influence of the heating rate on the temperature profiles in the sample and on the solid conversion rate has been studied. A mathematical model without adjustable parameters has been used to calculate the temperature at different points in the solid bed and the average total solid conversion. The experimental results have been compared with those calculated by the model. A good agreement has been obtained for sawdust. Some differences are observed for cellulose at high heating rates, and the influence of the thermal conductivity and the reaction heat on the results has been analysed. 相似文献
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Hakim F. Abbasov 《Journal of Dispersion Science and Technology》2019,40(4):594-603
Nanofluids having high thermal conductivity enhancement relative to conventional pure fluids are fluids engineered by suspending solid nanoparticles into base fluids. In the present study, calculating the Van der Waals interaction energy between a nanoparticle and an ordered liquid nanolayer around it, the nanolayer thickness was determined, the average velocity of the Brownian motion of nanoparticles in a fluid was estimated, and by taking into account both the aggregation of nanoparticles and the presence of a nanolayer a new thermal conductivity model for nanofluids was proposed. It has been shown that the nanolayer thickness in nanofluids is independent on the radius of nanoparticles when the radius of the nanoparticles is much greater than the nanolayer thickness and determines by the specific interaction of the given liquid and solid nanoparticle through the Hamaker constant, the surface tension and the wetting angle. It was proved that the frequency of heat exchange by fluid molecules is two orders of magnitude higher than the frequency of heat transfer by nanoparticles, so that the contribution due to the Brownian motion of nanoparticles in the thermal conductivity of nanofluids can be neglected. The predictions of the proposed model of thermal conductivity were compared with the experimental data and a good correlation was achieved. 相似文献
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A method based on the analysis of the temperature profiles is proposed to identify changes in the physical structure and/or in the chemical composition of a solid when a constant heat flow passes through it. This analysis is applied to natural carbonates which are important from an industrial point of view. The thermal conductivity of the calcined and non-calcined naturals carbonates is determined in order to relate variations in the temperature profiles with changes in the structure of the solids under study. A mathematical model, which predicts temperature profiles in spherical samples for heat transport processes similar to those studied, is proposed. This model is able to predict temperature profiles in heat transport processes, with or without chemical reaction, and with the chemical reaction fitting the progressive conversion model or the unreacted core one. 相似文献
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C.L. Chakrabarti Shaole Wu R. Karwowska J.T. Rogers R. Dick 《Spectrochimica Acta Part B: Atomic Spectroscopy》1985,40(10-12)
A simplified model for heat transfer based on thermal conduction is used to calculate the radial gas temperature distribution inside a semi-enclosed, commercial graphite tube furnace used for atomic absorption spectrometry. In the absence of a forced convective flow of a purge gas, the gas temperature inside the graphite furnace during its heating is lower than the wall temperature. After the wall temperature has attained a steady-state value, the gas temperature approaches the wall temperature and the radial temperature gradient in the gas decreases. The difference between the wall temperature and the gas temperature depends on the temperature program used, the thermal properties of the purge gas, and the atomizer geometry. The residence time of relatively volatile analyte elements is largely controlled by expulsion when wall atomization at high heating rates and high atomization temperatures are used. Analytical sensitivities are often enhanced by vaporizing the analyte into a gas having an approximately constant temperature. 相似文献
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The heat transfer mechanisms in inorganic hollow micro-spheres filled polymer composites are analyzed in the present paper. This heat transfer includes mainly three mechanisms: (1) thermal conduction between solid and gas; (2) thermal radiation between the hollow micro-sphere surfaces; and (3) natural thermal convection of the gas in the micro-hollow spheres. A theoretical model of heat transfer in polymer/inorganic hollow micro-sphere composites is established based on the law of minimal thermal resistance and the equal law of the specific equivalent thermal conductivity, and a corresponding equation of effective thermal conductivity is derived. The effective thermal conductivity (keff) of hollow glass bead-filled polypropylene composites is estimated by using this equation, and is compared with the numerical simulations by means of a finite element method. The results show that the variation of the theoretical estimations of keff are similar to the numerical simulations at lower filler volume fraction (φf20%). Moreover, keff decreases linearly with increasing φf, and reduces somewhat with increase of filler size. 相似文献
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Ionut Ledeti Gabriela Vlase Titus Vlase Nicolae Doca Vasile Bercean Adriana Fulias 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1057-1063
The thermo-physical properties for four rock types (granite, granodiorite, gabbro, and garnet amphibolite) from room temperature to 1,173 K were investigated. Thermal diffusivity and specific heat capacity were measured using the laser-flash technique and heat flux differential scanning calorimetry, respectively. Combined with the density data, rock thermal conductivities were calculated. Rock thermal diffusivity and conductivity decrease as the temperature increases and approach a constant value at high temperatures. At room temperature, the measured thermal conductivity is consistently near or lower than the calculated conductivity using the mineral series model, which suggests that real thermal conduction is more complicated than is depicted in the model. Therefore, in situ measurement remains the best method for accurately obtaining thermal conductivity for rocks. 相似文献
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F. Tian L. Sun J. E. S. Venart R. C. Prasad S. C. Mojumdar 《Journal of Thermal Analysis and Calorimetry》2008,94(1):37-43
Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate
of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy
of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables
contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude
of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements
of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous
measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However,
these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently
developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A
thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and
discussed. 相似文献