流化床液体分布器优化数学模型

本对化工生产中的流化床的液体密度分布进行了计算，并建立了流化床流体分布器的优化数学模型，提出了有效的解法，为提高化工生产效率提供了一种指导方法。     

Correlation of data concerning resistance to flow of generalized Newtonian fluids through granular beds

Summary The paper is concerned with the pressure drop during the flow of rheologically complex fluids through granular beds. An approach is proposed which enables the correlation of the data for any generalized Newtonian fluid. As an example, a detailed derivation of a correlation equation is presented for Carreau fluids. The applicability of the derived equation was proved experimentally in the case of flow of molten poly(ethylene terephthalate) through granular beds.

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Zusammenfassung Die Arbeit betrifft den Druckverlust bei der Strömung von Flüssigkeiten mit komplexen rheologischen Eigenschaften durch Kornschüttungen. Es wird ein Verfahren vorgeschlagen, das eine Korrelation der Daten für beliebige verallgemeinerte newtonsche Flüssigkeiten ermöglicht. Als Beispiel wird die Ableitung der Korrelationsgleichung für Carreau-Flüssigkeiten ausführlich dargestellt. Die Anwendbarkeit der abgeleiteten Gleichung wird für die Strömung von geschmolzenem Polyäthylenterephthalat durch Kornschüttungen experimentell bestätigt.

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a _T temperature shift factor - A constant in eq. [1] - b _M molecular weight shift factor - d _p effective particle diameter, m - D capillary diameter, m - f _BK friction factor, defined by eq. [4] - K constant in eq. [22] - K ₀ constant depending on the shape of a conduit cross-section - K ₁ constant in eq. [11] - l bed height, m - l _e average length of the bed channels, m - L length of a conduit, m - M _n number-average molecular weight - M _w weight-average molecular weight - N constant in Carreau model - p pressure drop due to friction, Pa - r _h hydraulic radius, m - T absolute temperature, K - v mean linear velocity, m/s - v _e mean linear velocity in the bed channels, m/s - v ₀ superficial velocity, related to an empty cross-section of the column, m/s - dimensionless factor, defined by eq. [21] - shear rate, s^–1 - nominal shear rate at the wall of a circular pipe, s^–1 - average shear rate at the wall of a noncircular channel, s^–1 - bed porosity - shear dependent viscosity, Pa s - ₀ zero-shear rate viscosity, Pa s - infinite-shear rate viscosity, Pa s - [] intrinsic viscosity - time constant in Carreau model, s - µ Newtonian viscosity, Pa s - fluid density, kg/m³ - _w shear stress at the wall of a circular pipe, Pa - average shear stress at the wall of a noncircular channel, Pa - {Re} general form of Reynolds number in eq. [1] - Re _BK modified Reynolds number for Newtonian fluids, defined by eq. [25] - Re _BK ^* generalized Reynolds number for Carreau fluids, defined by eq. [24] With 5 figures and 2 tables     

SiO2气凝胶薄膜常压制备与强化研究

采用溶胶凝胶技术,结合碱性催化和低表面张力溶剂交换以及非活性CH3基团置换修饰,在常压条件下成功地制备了孔隙率为77%、折射率为1.12纳米多孔SiO2气凝胶薄膜.采用氨和水蒸气混合气体热处理技术提高薄膜的耐磨性、附着力等力学特性.使用透射电镜(TEM)、扫描电镜(SEM)分别观察了溶胶的颗粒结构和薄膜表面形貌.应用傅里叶转换红外光谱仪(FTIR)研究了薄膜经表面基团修饰前后的红外吸收光谱以及后处理对薄膜红外ω4(TO3)吸收峰位置和半宽度的影响.采用椭偏仪测量薄膜的厚度和折射率.耐摩擦和附着力测试表明: 关键词： SiO_2气凝胶薄膜 溶胶凝胶技术 纳米多孔结构     

掺钛化学腐蚀法制备发光稳定的多孔硅

本文采用掺钛化学腐蚀法制备出了发光稳定性和均匀性都较好的多孔硅 (PS)。存放和退火试验表明 ,光致发光 (PL)谱峰位不蓝移 ,强度不衰减。多孔硅发光稳定性的提高归因于制备过程中样品表面原位氧和钛的钝化。钛的浓度和腐蚀时间对PL强度有明显影响 ,最佳钛浓度约为 0 0 8mol·L- 1 ,最佳腐蚀时间约为 2 0min。掺钛化学腐蚀法制备的PS的光激发过程符合量子限域机制 ,而其PL过程却与量子限域模型不符 ,这表明其光发射过程不是带 带直接跃迁产生的 ,即存在一个表面态     

活性炭-氨吸附式制冷循环中吸附床的传热传质性能研究

吸附床由6个吸附单元组成,吸附单元为壳管式换热器,吸附工质对是活性炭-氨。利用多孔介质中流体流动的概念,建立一个吸附单元的数学模型,模拟结果与实验结果显示出很好的一致性。同时得出了吸附床内某种平均温度和平均压力的分布规律。     

Finite element analysis of convective heat transfer in porous media

The finite element method is used to analyse convective heat transfer in a porous medium. Convection past a vertical surface embedded in the medium and convection in a confined porous medium enclosure are analysed using the above method. The results are compared with those available in the literature and the agreement is found to be good. The method is applicable for two-dimensional analysis in a porous body of any arbitrary shape. The restriction of the boundary layer assumption is relaxed.     

Free and forced convection flow in a rotating channel bounded below by a permeable bed

The steady flow in a parallel plate channel rotating with an angular velocity Ω and bounded below by a permeable bed is analysed under the effect of buoyancy force. On the porous bed the boundary condition of Beavers and Joseph is applied and an exact solution of the governing equations is found. The solution in dimensionless form contains four parameters: The permeability parameterσ ², the Grashof numberG, the rotation parameterK ² and a dimensionless constantα. The effects of these parameters, specially,σ ², G andK ², on the slip velocities and velocity distributions are studied. For largeK ², there arise thin boundary layers on the walls of the channel.     

SYNTHESIS AND APPLICATION OF NANOPARTICLES BY A HIGH GRAVITY METHOD

Fast chemical reactions involved in nanomaterials synthesis, polymerization, special chemicals production, reactive absorption, etc., are often difficult to control in terms of product quality, process efficiency and production consistency.After a theoretical analysis on such processes based on chemical reaction engineering fundamentals, an idea to intensify micromixing (mixing on the molecular scale) and mass transfer and therefore to control the process ideally was proposed.By experimental investigations of mass transfer and micromixing characteristics in the Rotating Packed Bed (RPB, or “HIGEE“ device), we achieved unique intense micromixing. This led us to the invention of using RPB as a reactor for the fabrication of nanoparticles (Chen et al., 2000).RPB consists mainly of a rotating packed rotator inside a stationary casing. The high gravity environment created by the RPB, which could be orders of magnitude larger than gravity, causes aqueous reactants going through the packing to spread or split into micro or nano droplets, threads or thin films, thus markedly intensifying mass transfer and micromixing to the extent of 1 to 3 orders of magnitude larger than that in a conventional packed bed.In 1994, the first RPB reactor was designed to synthesize nanoparticles of CaCO3 through multiphase reaction between Ca(OH)2 slurry and CO2 gas, and nanoparticles of 15～30nm in mean size and with very uniform particle size distribution was obtained. In 1997, a pilot-scale RPB reactor was successfully set up for operation, and in 2000, the first commercial-scale RPB reactor for synthesis of such nanoparticles came into operation in China, establishing a milestone in the use of RPB as a reactor for the fabrication of nanomaterials (Chen et al., 2002).Since then, the high gravity method has been employed for the synthesis of inorganic and organic nanoparticles via gas-liquid, liquid-liquid, and gas-liquid-solid multiphase reactions, e.g. inorganic nanoparticles like nanosized CaCO3, TiO2,SiO2, ZnO, Al2O3, ZnS, BaTiO3, BaCO3, SrCO3, Al(OH)3 and Mg(OH)2 flame retardants, and organic nano-pharmaceuticals including benzoic acid, salbutamol sulfate and cephradine. This technology received extensive attention in the field of nanomaterials fabrication and application. Dudukovic et al. commented, “The first large-scale application of RPB as a reactor occurred in China in production of nano CaCO3 by HGRP (high gravity reactive precipitation)of carbon dioxide and lime. Uniformly small particles were made in the RPB due to achievement of a sharp supersaturation interface and very short liquid residence times in the device.“ (Dudukovic et al., 2002). Date et al. said, “HGRP represents a second generation of strategies for nanosizing of hydrophobic drugs. In our opinion, among various methodologies described eariier, supercritical anti-solvent enhanced mass transfer method and HGRP method has potential to become technologies of the future owing to their simplicity, ease of scale-up and nanosizing efficiency“ (Date et al., 2004).As-synthesized nano CaCO3 was employed as a template to synthesize silica hollow spheres (SHS) with mesostructured walls. Characterizations indicated that the obtained SHS had an average diameter of about 40 nm with a surface haviors of Brilliant Blue F (BB), which was used as a model drug. Loaded inside the inner core and on the surfaces of SHS,BB was released slowly into a bulk solution for as long as 1 140min as compared to only 10min for the normal SiO2nanoparticles, thus exhibiting a typical sustained release pattern without any burst effect. In addition, higher BET value of the carrier, lower pH value and lower temperature prolonged BB release from SHS, while stirring speed indicated little influence on the release behavior, showing the promising future of SHS in controlled drug delivery (Li et al., 2004).Nano-CaCO3 synthesized by the high gravity method was also employed as a filler to improve the performance of organic materials. By adding CaCO3 nanoparticles into polypropylene-ethylene copolymer (PPE) matrix, the toughness of the matrix was substantially increased. At a nanosized CaCO3 content of 12 phr (parts per hundred PPE resin by weight),matrix. In the nanosized CaCO3/PPE/SBS (styrene-butadiene-styrene) system, the rubbery phase and filler phase were independently dispersed in the PPE matrix. As a result of the addition of nanosized CaCO3, the viscosity of PPE matrix significantly increased. The increased shear force during compounding continuously broke down SBS particles, resulting in the reduction of the SBS particle size and improving the dispersion of SBS in the polymer matrix. Thus the toughening effect of SBS on matrix was improved. Simultaneously, the existence of SBS provided the matrix with good intrinsic toughness, satisfying the condition that nanosized inorganic particles of CaCO3 efficiently toughened the polymer matrix,thus fully exhibiting the synergistic toughening function of nanosized CaCO3 and SBS on PPE matrix (Chen et al., 2004).As-prepared nano-CaCO3 was blended with TiO2 and other additives to prepare complex master batches for use in the coloring of polypropylene. It was found that the obtained nano-CaCO3 is an excellent pigment dispersant, which can partially replace TiO2 pigments for polypropylene resin coloring. Nano-CaCO3 can prompt the dispersion of TiO2 in polymer matrix, boosting the whiteness of the materials without a negative effect on the UV absorbency of the materials (Guo et al.,2004). Studies on the mechanical properties of nano-CaCO3 toughened epoxy resin composite indicated that impact strength and flexural modulus of the composite improved remarkably when 6wt.% of nano-CaCO3 was added. Surface treatment of nano-CaCO3 by titanate coupling agents significantly improved the dispersibility of nano-CaCO3 in such a high viscous matrix (Li et al, 2005).     

A fully coupled numerical technique for 2D bed morphology calculations

A fully coupled two‐dimensional subcritical and/or supercritical, viscous, free‐surface flow numerical model is developed to calculate bed variations in alluvial channels. Vertically averaged free‐surface flow equations in conjunction with sediment transport equation are numerically solved using an explicit finite‐volume scheme using transformed grid in order to handle complex geometry fluvial problems. Convergence is accelerated with use of a multi‐grid technique. Firstly the capabilities of the proposed method are demonstrated by analyzing subcritical and supercritical hydrodynamic flows. Thereafter, an analysis of one‐ and two‐dimensional flows is performed referring to aggradation and scouring. For all reported test cases the computed results compare reasonably well with measurements as well as with other numerical solutions. The method is stable, reliable and accurate handling a variety of sediment transport equations with rapid changes of sediment transport at the boundaries. Copyright © 2002 John Wiley & Sons, Ltd.