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71.
Liquid propylene was polymerized in a 5‐L autoclave batch reactor using a commercially available TiCl4/MgCl2/Al(ethyl)3/DCPDMS Ziegler–Natta catalyst, with a phthalate ester as internal electron donor. The powders from these polymerizations were characterized using laser diffraction particle size distribution (PSD) analysis, scanning electron microscopy (SEM), and bulk density measurements. These characteristics were analyzed as a function of the process conditions, including hydrogen and monomer concentration, polymerization temperature, and the prepolymerization method. It was shown that polymerization temperature influences the powder morphology to a large extent. At low temperatures, high‐density particles were obtained, showing regular shaped particle surfaces and low porosities. With increasing temperature, the morphology gradually was transferred into a more open structure, with irregular surfaces and poor replication of the shape of the catalyst particle. When using a prepolymerization step at a relatively low temperature, the morphology obtained was determined by this prepolymerization step and was independent from conditions in main polymerization. The morphology obtained was the same as that observed after a full polymerization at temperature. Even when using a short polymerization at an increasing temperature, the morphology was strongly influenced by the initial conditions. The effect of variation in hydrogen concentration supported the conclusion that the initial polymerization rate determines the powder morphology. In the absence of hydrogen, high bulk densities, and regularly shaped particles were obtained, even at high temperatures. With increasing hydrogen concentration, the reaction rates increased rapidly, and with that changed the morphology. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1421–1435, 2003 相似文献
72.
Micrometer–nanometer hydrophobic titania–fluoroalkylsilane composite coatings were prepared on substrates based on liquid‐phase deposition. Coatings and crystallization forms were characterized with instruments of surface analyses. Experimental facilities of pool boiling were established to evaluate heat and mass transfer on coated surfaces in deionized water and saturated calcium carbonate solution. Obvious pool boiling enhancement was observed on thinner microscale–nanoscale hydrophobic titania–fluoroalkylsilane composite films at higher heat fluxes compared to that on thicker titania–fluoroalkylsilane coatings or on titania coatings and stainless steel surfaces. Lower fouling resistance was obtained on titania–fluoroalkylsilane coatings in pool boiling of saturated calcium carbonate solution and crystal form was aragonite, which was different from calcite on titania coatings. Results of inhibition of fouling and enhancement of heat transfer on titania–fluoroalkylsilane coatings were contributed to special surface microscale–nanoscale structure and material wettability. Asymptotic model was used to fit experimental data of fouling resistance, and reasonable agreement was obtained. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2662–2678, 2013 相似文献
73.
A kinetic model for simulation of the MTO process over SAPO-18 catalyst in a wide range of operating conditions has been proposed. The kinetic model predicts the experimental evolution of reaction products with time on stream, which follows three consecutive periods: initiation (where olefin production increases), a period of maximum olefin production and a period in which this production decreases. The kinetic scheme takes into account these three steps that evolve with time on stream: formation of active intermediate compounds, an step where olefins are formed by reaction of oxygenates (methanol/DME) with these intermediates and deactivation of intermediates by degradation to coke. The presence of water in the reaction medium attenuates the reaction rate of these steps. Discrimination of kinetic equations and calculation of the parameters of best fit have been carried out by solving the mass conservation equations of the individual components of the kinetic scheme together with the kinetic equation for deactivation and taking into account the effect of water on the kinetics of each step. 相似文献
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Drift velocity is a very important paramcter for predictirg the pool volumetric void fraction. Two-phase system of gas and high viscous liquids pool is encountered in various engineering applications. A review of the literature shows no data for explaining the effect of highly viscous liquids on the drift velocity. This paper's analysis shows that there is a considerable influence. It is shown that the foaming behaviour of liquids is dependent on the surface properties. For some highly viscous liquids at a given superficial gas velocity, the viscosity changes with time. The effect of "foam" and "time" on drift velocity is clearly elucidated. 相似文献
77.
用小直径颗粒床改善池内沸腾的热滞后特性 总被引:4,自引:0,他引:4
对水平表面上小直径颗粒床的饱和池沸腾传热做了实验研究,发现热滞后特性获得了重大的改善,使温度过头现象可以消除,因而这种方法可能用以改进微电子元件的冷却。但沸腾传热在高热流下比平板时明显恶化。 相似文献
78.
川西坳陷T3成藏主控因素与有利勘探区带分析 总被引:14,自引:0,他引:14
分析了川西坳陷上三叠统油气富集、成藏的主控因素 .通过对烃源岩分布与演化、古构造、古隆起的分析以及对裂缝和保存条件等因素的系统研究 ,划分出了有利勘探区带 .结果表明 ,上述因素对上三叠统成藏具有控制作用 ;灌口—平落坝、大兴鼻状隆起、孝泉—丰谷、中坝—鸭子河、老关庙—九龙山构造带为构造圈闭领域有利勘探区带 ;川西—川中过渡带内须二段地层尖灭带为岩性圈闭领域有利勘探区带 相似文献
79.
为了掌握双激光束双侧同步焊接工艺特性并得到最优焊接工艺匹配参数,对由铝合金6156底板与6056桁条组成的T型焊接接头进行了有限元数值模拟和试验研究.在改进以往激光热源模型的基础上,模拟分析了不同工艺参数匹配条件下的激光焊接过程,获得了实际可行的工艺参数范围.同时研究了焊接功率和焊接速度对熔池形状的影响规律,结果表明:焊接功率和焊接速度对焊缝成形具有重要影响,且熔池形状的模拟结果与试验结果吻合良好.最终获得了最佳的焊接工艺参数,为大型客机铝合金壁板的双激光束双侧同步焊接提供了理论指导. 相似文献
80.
为加强电力接入通信网络的建设,更好地满足电力应用的需求,依托电力系统已有专用光纤和无线通信资源,并借鉴分布式基站在公网通信中的建设模式,提出基于分布式基站池的电力光载无线通信系统。将基带处理单元以池的形式进行划分管理,并以分布式的方式进行信息交互和数据处理,同时,从远端单元侧、传输通道侧及基站池侧三个方面来实现基于认知的资源优化调度使用。理论分析表明,新系统可充分利用电力专用通信资源,适应电力通信接入网网架结构。 相似文献