共查询到20条相似文献,搜索用时 125 毫秒
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将Fick扩散定律的Fourier三角级数算法推广成多孔材料分形扩散模型的Fourier-Bessel级数算法,并把它应用于化学工程中吸附问题涉及的浓度分布与相对吸附量的计算中,取得一些规律性认识.由于分形扩散模型是在Fick扩散定律的基础上增加了表征微观结构的参数df和θ,研究多孔材料中的浓度分布与相对吸附量时,与Fick扩散定律的研究结果相比,定性上基本一致,在定量上有差别,df和θ对扩散传质过程的影响各有侧重,用它们可更好地描述多孔材料中的扩散过程. 相似文献
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利用Monte Carlo模型研究了薄膜生长初始阶段岛的形貌与基底温度之间的关系,同时还研究了它们与汽相粒子入射剩余能量之间的关系.模型中考虑了三种动力学过程:粒子入射、吸附粒子扩散和粒子脱附,与以前薄膜生长模型的不同之一在于把入射过程看作独立于其他过程,而扩散和脱附过程是相互关联的.结果表明随基底温度的升高,岛的形貌经历了一个从分散生长、分形生长到凝聚生长的变化过程.低温下随汽相粒子入射和剩余能量增加,岛的形貌也经历了同样的变化过程.
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通过碱沉淀法制备了Ce,Al,Ni,Cu的水合氧化物,研究了它们的Langmuir吸附等温线,并利用BET法通过吸附-脱附氮气测定了其比表面积,同时对其吸附氟离子前后的变化进行了IR谱图的表征.结果表明不同水合金属氧化物具有不同的比表面积,其孔径分布也不尽相同,吸附量与比表面积之间没有直接相关的正比关系.吸附等温线均符... 相似文献
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Soon-Jae Lee Seung-Gun Chung Dong-Ju Kim Cheol Eui Lee Jae-Woo Choi 《Current Applied Physics》2009,9(6):1323-1325
We proposed a new method from which kinetic sorption parameters can be estimated using aqueous phase concentration versus time data commonly available from adsorption tests. The method relies on the analytical solution that was solved for two-site reversible sorption kinetics based on mass conservation law for solute in a batch reaction system. In order to validate the method, model parameters were compared with those of three-stage kinetic models available in the literature. It was revealed that model parameters of the two-site kinetics could accurately be estimated as much as other model parameters. Advantage of the new method is acquisition of additional parameter, distribution or partitioning coefficient (Kd) frequently used in the analysis of chemical transfer in the solid–liquid interface. 相似文献
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Understanding the environmental behavior of nanoparticles includes their interaction with biofilms, which is a covering on the surface of a living or nonliving substrate composed of microorganisms. This study focuses on nano-TiO2 sorption mechanism by synthetic biofilm that was prepared as superporous spherical beads from agarose, using batch stirred flasks kept at room temperature. The pH plays an important part in these phenomena, by its influence on the nanoparticles and biofilm chemistry, where the biofilm nanoTiO2 uptake at neutral pH was enhanced over acidic conditions. Hydroxylation of TiO2 nanoparticles, dependent on pH and the salinity of the solution, influences the stability of colloids, the sorption kinetics via the nature of limiting phases: diffusion through the boundary layer or intrabiofilm mass transfer and the sorption mechanism. The sorption follows pseudo first-order adsorption kinetics with estimated average rate constants of 2.2 (min? 1). Equilibrium isotherms were evaluated using Langmuir and Freundlich isotherms to obtain the maximum uptake at different solution pH and the free energy of the adsorption. The adsorption is apparently irreversible because biofilm limits diffusion of particles out of the pores and the complexation active binding sites on the surface hydrated biofilm to the hydrophilic TiO2 nanoparticles. 相似文献
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The computer model of the initial stage of condensation processes is developed. The stochastic processes of adsorption, surface
diffusion, and desorption occur on the 70×70 lattice of adsorption vacancies. The model was tested by an example close to
water vapor sorption on a conventional crystal surface. Computed results demonstrate the processes of nucleation, growth of
crystals, and developed condensation. Computations were carried out for various adsorption energies. Results showed that with
decreasing energy of adsorption the character and rate of nucleation and subsequent condensation vary. With decreasing energy
of adsorption the probability of nucleation of islets on substrate reduces, the filling of the next atomic layers on islets
occurs earlier than the filling of the substrate, the growth rate of islets in height increases as compared to condensation
of a continuous film, and the growth rate of area of islets decreases. There is a typical energy of adsorption at which the
growth rate of islets in height reaches its maximum. At a further drop of adsorption energy, there is a growth of islets only
in height, the growth rate, however, reduces. The phenomena revealed in computations illustrate the mechanism of origin of
columnar and filamentary crystals. 相似文献
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《Heat Recovery Systems and CHP》1988,8(6):537-548
A mathematical model describing the heat and mass transfer processes that occur during sorption of water vapor in a dehumidifier consisting of parallel channels lined on either side width desiccant felt, is presented. The model includes both gas-side and solid-side resistances for thermal and mass transport. The moisture transport in the desiccant is expressed by considering both gas phase diffusion and surface diffusion. The heat and mass transfer in the desiccant matrix occurs simultaneously and is coupled by an equilibrium sorption relation which is applied locally within the desiccant. Solutions are obtained by using an explicit finite-difference scheme.The effect of heat and mass transfer Biot numbers and other system parameters on the performance of an adiabatic open-cycle cooling system are investigated. 相似文献
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The bulk resistivity, annealing temperature and photo-illumination were found to have large effects on the oxygen sorption of the Cd (0001) surfaces of CdSe. For the higher resistivity surfaces, annealing at temperatures below ~ 400°C, no oxygen adsorption was detected. However, if the surfaces were annealed at temperatures above ~ 500°C, a significant amount of oxygen adsorption was subsequently detected at room temperature in darkness. This adsorbed oxygen could be partially desorbed by visible light and almost completely desorbed by UV light. On the other hand, surfaces of very low resistivities were so much more reactive to oxygen that appreciable oxygen adsorption in darkness was detected. This oxygen adsorption was always enhanced by illumination with UV or visible light. Annealing at ~ 550 °C had no significant effect on this photo-adsorptive behaviour. However, annealing at temperatures ~ 500–550°C decreased the diffraction intensity. Based on mass spectrometer analysis, the decrease in diffraction intensity was interpreted as due to diffusion of excess Cd to the surface. The oxygen sorption behaviours of all the surfaces investigated were adequately explained by the existing theories based on charge transfer between the surfaces and the adsorbed oxygen. 相似文献
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《Heat Recovery Systems and CHP》1993,13(4):341-346
Periodically operating dry sorption machines utilize the reaction enthalpies of suitable reversible adsorption and absorption reactions for the generation of useful heat and cold. Typical working materials are ammoniated salts (chlorides in connection with ammonia), zeolites (with water), activated carbon (with methanol), metal hydrides (with hydrogen). The key elements of such machines are the reaction beds, typically cylindrical tubes, in which ad(ab)sorption and desorption takes place, or in which the ad(ab)sorbant is condensed and evaporated. The heat and mass transfer inside these reaction beds is decisive for the operational characteristics of respective machines. An overview is given of typical designs of the reaction beds. Special emphasis is given to heat transfer enhancement techiques inside the reaction beds. The external heat transfer from and to the reaction bed wall is also addressed. 相似文献
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Adsorption kinetics of 4-chlorophenol onto granular activated carbon in the presence of high frequency ultrasound 总被引:1,自引:0,他引:1
This work describes the results of investigations carried out to examine the adsorption kinetics of 4-chlorophenol (4-CP) from aqueous solution containing tert-butyl alcohol (10%, v/v) onto granular activated carbon (GAC) in the presence of ultrasound of different high frequencies (516, 800 and 1660 kHz) and acoustic powers (15.2, 21.5, 31.1 and 38.3 W). The main objective of this study is to describe the mechanism of ultrasound-assisted adsorption rather than the enhancement of adsorption capacity. Sonochemical degradation of 4-CP was studied in the absence and presence of tert-butyl alcohol. The sonolysis of 4-CP is effectively inhibited by the addition of tert-butyl alcohol (10%, v/v) and very little 4-CP degradation occurs, indicating that little or no pyrolysis of the compound occurs. Without addition of tert-butyl alcohol, after 300 min and at 1660 kHz, the removal of 4-CP in the presence of ultrasound for an acoustic power of 38.3 W was nearly total (99%), but in the conventional method only 60% was eliminated. In this case, the removal of 4-CP by GAC in the ultrasound-assisted technique is due to both adsorption and ultrasonic degradation, but the removal by simple stirring is only due to adsorption, which makes a direct comparison unacceptable. In order to distinguish sonochemical degradation and adsorption of 4-CP onto GAC and to make an exact and practical comparison of the adsorption in the absence and presence of ultrasound, kinetic adsorption experiments were conducted using aqueous solution containing 10% (v/v) tert-butyl alcohol. The obtained results show that both adsorption rate and adsorbed amount were significantly enhanced and improved in the presence of ultrasound for all the studied frequencies and powers. The enhancement of adsorption is favored by increasing ultrasonic power. Adsorption kinetic data were modeled using the liquid-film mass transfer equation and intraparticle diffusion model. The values of the intraparticle diffusion coefficient obtained in the presence of ultrasound are greater than that obtained in the absence of ultrasound. In the initial period of adsorption, where external mass transfer is assumed to predominate, liquid-film mass transfer coefficients significantly increased by the assistance of ultrasound. These results indicate that ultrasound enhances the mass transport in the pores as well as across the boundary layer. This effect increased with increasing ultrasonic power for the three studied frequencies. The average order for the studied ultrasonic waves according to the initial adsorption rate, the intraparticle diffusion coefficient and the liquid-film mass transfer coefficient is 516 kHz>800 kHz>1660 kHz. 相似文献
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Shiquan Lin Jing Yang Jiefeng Yan Yaping Zhao Bin Yang 《Journal of Macromolecular Science: Physics》2013,52(2):286-300
A gravimetric method was used to study the sorption and diffusion of supercritical carbon dioxide in a temperature range from 40°C to 80°C and a pressure range from 8.0 to 18.0 MPa in a biodegradable polymer, namely poly(butylene adipate-co-terephthalate) (PBAT). The PBAT presented Fickian behavior and Fick's diffusion model was applied to determine the amount of carbon dioxide present in the samples after a predetermined exposure time as well as the diffusion coefficients. The variations of diffusion coefficients of CO2 for the sorption under supercritical conditions and desorption at ambient conditions as well as equilibrium sorption amounts of CO2 with variations of pressure and temperature were determined and compared. 相似文献
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Linhai Duan Xiaotong Zhang Ke Tang Lijuan Song Zhaolin Sun 《Applied Surface Science》2005,250(1-4):79-87
The adsorption isotherm, differential thermal gravimetry (DTG), thermal gravimetry (TG), diffusion and thermodynamic parameters of cyclopentane at various adsorption coverages have been investigated using microgravimetric technique over a range of temperature. The differences in equilibrium adsorption capacity and in diffusion coefficient at different temperature are discussed in terms of the characteristics of silicalite-1 and the features of cyclopentane molecule. The heat of sorption Qst varies significantly with sorption coverage indicating that the adsorption and diffusion mechanism is complex. The dependences of thermodynamic properties like free energy change (ΔG) and entropy change (ΔS) on sorption coverage show a sharp decrease and increase suggesting that the adsorption sites of the silicalite-1 are not energetically uniform to cyclopentane. Two desorption peaks in the DTG and TG curves suggest that two heterogenous binding sites surely exist in silicalite-1 to cyclopentane. 相似文献