共查询到18条相似文献,搜索用时 156 毫秒
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通过细乳液聚合,在正辛烷液滴外包覆一层苯乙烯与甲基丙烯酸-3-三甲氧基硅丙酯(MPS)的共聚物,得到一种新型有机-无机杂化纳米微胶囊.用透射电镜(TEM)和原子力显微镜(AFM)表征了其形态;用气体吸附仪(BET)研究了其微观结构,发现其具有多孔结构.利用多孔介质中的孔道扩散理论对其渗透过程进行建模,微胶囊渗透过程中的主体扩散系数主要由其孔隙率和曲折因子决定.用紫外可见分光光度计(UV)研究了微胶囊在不同体系中的渗透动力学,计算得到了各种条件下渗透的主体扩散系数和曲折因子,发现溶质的扩散速率随微胶囊中MPS用量增加造成的孔隙率增大而增加;曲折因子在甲酚红-甲醇体系中比在蒽-四氢呋喃体系中小,且基本不随微胶囊中MPS用量变化,与用孔道扩散理论分析结果一致.用红外光谱(IR)证实了示踪剂确实装载进入了微胶囊,但示踪剂的释放速率比装载速率小得多,且主体扩散系数随MPS用量变化不大. 相似文献
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多孔介质干燥的孔道网络试验及模拟 总被引:4,自引:0,他引:4
结合孔道网络及侵入渗流理论。试验并模拟研究了刚性多孔介质的干燥过程。观察了孔道网络内部湿组份的分布状态,孔道网络干燥前沿的形成及发展过程。验证了多孔介质在干燥过程出现的蒸发前沿及其具有的不规则特征。模拟研究了多孔介质在等温条件下不考虑重力时的干燥过程。通过模拟给出了多孔介质在干燥过程内部相的动态分布。模拟结果显示,干燥前沿具有非常不规则的特征。通过相图分析。干燥中内部涅分的迁移不仅是一个从里到外的过程。也同时存在逆向扩散。 相似文献
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对砂粒堆积床这一自然多孔介质的结构特性及孔道网络干燥模型进行了描述,并对砂粒堆积床结构参数与孔道网络模型参数进行了对应分析;建立了堆积床的孔道网络模型,并利用该模型进行了砂堆积床干燥过程的孔道网络模拟;模拟的结果与干燥实验数据进行了验证。 相似文献
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在两种氧化铝中 ,分别采用C2H4 、Ar和CO2 进行了两组分和三组分的Wicke -Kallenbach定态扩散实验 .由尘气模型和Stefan -Maxwell方程建立起的扩散通量方程 ,对实验结果加以处理 ,得到了两组分扩散的有效扩散系数及三组分扩散的虚拟两组分有效扩散系数 .同时 ,针对过渡区扩散推出了等温下两组分扩散的有效扩散系数为常数应满足的基本条件 ,所得结论和实验结果相吻合 .而对三组分扩散中的虚拟两组分有效扩散系数不能按照常数处理 .此外 ,无论是两组分或三组分扩散 ,对每一种氧化铝而言 ,有着相近的曲折因子 ,从而证实了曲折因子是与多孔介质结构密切相关的参数 相似文献
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干燥过程原理研究概况 总被引:3,自引:0,他引:3
介绍了多孔介质湿分迁移的液相流动、毛细流动、蒸汽流动、液相扩散、蒸汽扩散等理论的基本论点及其存在的不足。认为借用侵入渗流理论及孔道网络方法研究多孔介质的干燥问题,有望取得新突破。 相似文献
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G. Knaff E. U. Schlü nder 《Chemical Engineering and Processing: Process Intensification》1987,21(4):193-197
The internal mass transfer resistance was measured by dissolving naphthalene from a porous insoluble rod in a stream of supercritical carbon dioxide. Initially the pores of the porous medium (sintered bronze) were filled with naphthalene. During dissolution the naphthalene surface retreats into the porous rod and the length of the diffusion path increases. The tortuosity factor for the porous material was determined from experimental data. The temperature was varied from 35 to 55 °C, the pressure from 118 to 226 bar and the mean pore diameter was either 8 or 20 μm. The results show that the tortuosity factor does not depend on the pressure and pore diameter. This result was to be expected since the mean free path of the molecules is much smaller than the pore diameter. The average tortuosity factor, however, decreased with increase of temperature. From this temperature dependence surface diffusion of the solute absorbed on the pore wall is concluded to take place and thereby to contribute to the observed overall rate of mass transfer. 相似文献
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According to the simulation of nitrogen sorption process in porous media with three-dimensional network model, and the analysis for such a process with percolation theory, a new method is proposed to determine a pore structure parameter--mean coordination number of pore network, which represents the connectivity among a great number of pores. Here the “chamber-throat“ model and the Weibull distribution are used to describe the pore geometry and the pore size distribution respectively. This method is based on the scaling law of percolation theory after both effects of sorption thermodynamics and pore size on the sorption hysteresis loops are considered. The results show that it is an effective procedure to calculate the mean coordination number for micro- and meso-porous media. 相似文献
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Gerasimos S. Armatas 《Chemical engineering science》2006,61(14):4662-4675
An efficient computation method to study flow and transport process of small molecules in porous media using a dual site-bond lattice model, DBSM, is described. The microscopic properties of the porous network take into account the influence of local heterogeneities during the simulations. The numerical experiments demonstrated the combined effect of pore size distribution and connectivity distribution on the mass transport properties and the structural tortuosity. The results indicate that the pore size distribution and percolation phenomena related with pore shielding effects, influence significantly the tortuosity and the effective diffusivity of the porous network. Also, the simulations raise the important role of the connectivity distribution among the various pores in the gas diffusive properties of the poorly connected networks. 相似文献
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《Applied catalysis》1981,1(3-4):185-200
Structural characterization of eleven kinds of aluminas prepared by different methods was carried out by measurement of the adsorption of nitrogen, X-ray diffraction and scanning electron microscopy. Aluminas prepared using aqueous ammonia as precipitation reagent exhibited a single pore size distribution, the maximum being at a radius of about 20Å, whereas aluminas prepared with urea exhibited a twin peaked pore size distribution, with maxima at radii of about 20Åand 50Å. The pore structures of aluminas prepared from aluminium nitrate by pyrolysis and from sodium aluminate with carbon dioxide were similar to the former, while aluminas prepared by pyrolyses of aluminium isopropoxide and of aluminium trichloride had a pore structure similar to the latter.Based on scanning electron microscopy and nitrogen adsorption-desorption hysteresis loop observations, the crystallite structures of aluminas and pore structures were discussed in connection with the preparation methods employed. 相似文献
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Diffusion properties of carbon dioxide-expanded toluene in bulk and confined to nanoporous glasses have been assessed using pulsed field gradient technique of NMR. In the bulk phase the diffusivity of toluene is found to increase significantly with increasing carbon dioxide content. The same dependence is observed in the mesoporous glass with large pore size, but with lower absolute values resulting from the tortuosity of the porous matrix. In contrast, in the porous glass with small pore size, strong confinements lead to different behavior due to an altered equilibrium phase composition in the pore space affecting the mass transfer rates. 相似文献
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《Chemical engineering science》1987,42(7):1565-1576
Stochastic pore networks have been used to interpret the effects of pore structure on simultaneous diffusion and reaction in a porous catalyst. A stochastic pore network is a square network of pores, each pore segment having a radius assigned at random from any stipulated pore size distribution. The equations for diffusion and reaction within the network are solved rigorously for first order irreversible kinetics. The model is used to predict effectiveness factors and tortuosities for a hypothetical catalyst having one of four pore size distributions. The analysis predicts that tortuosity will vary with the Thiele modulus, the strength of this variation depending on the pore size distribution. It is further observed that the concentrations experienced by pores in a network are markedly different to those predicted by the parallel bundle model. This is relevant to the question of selectivity in complex reaction schemes. 相似文献
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《Separation and Purification Technology》2003,30(1):11-26
Effect of the coordination number of the pore-network structure on the transport and deposition of colloidal particles in porous media was investigated. Applying with the orthogonal collocation principle and the pseudo-spectral method based on the Chebyshev polynomial, the complete solutions of the population balance equations describing the deposited particles, the suspended particles and the unblocked pore throats of porous media were obtained for the simple square network and the capillary tube network. It is shown that the network structure of porous media may significantly affect filtration rate, and therefore the effluent concentration and pressure drop. The filter with a capillary tube network structure owns higher filter coefficient than that of the filter with a simple square network structure. Theoretical predictions for different influent concentrations of particles, different flow rates and the case of blocking occurred in the filter bed are in agreement with the available experimental data. 相似文献