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1.
A theoretical approach is presented that describes membrane distillation processes due to the simultaneous action (in a proactive or in a counteractive way) of temperature and concentration differences through porous hydrophobic membranes. The model developed emphasizes the importance of the boundary layers, shows the existence of a coupling term between the two thermodynamic forces acting on the system, and permits the definition and characterization of the so-called steady states. In order to check the model, two membranes have been studied in different experimental conditions. The influence of some relevant parameters, such as solution concentration, stirring rate, mean temperature and temperature difference has been considered and the theoretical predictions of the model have been applied to the obtained results. The accordance may be considered good. 相似文献
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A new experimental method to obtain internal pressure profiles in a hollow fiber membrane was demonstrated. The experimentally obtained internal pressure profiles were compared with the theoretically calculated ones based on Hagen–Poiseuille equations. The experimental and theoretical results agreed very well in clean water conditions only when accurate membrane permeabilities and effective internal diameters were available. New experimental methods to obtain the two parameters were demonstrated. The same experimental technique was also applied for the submerged hollow fiber membranes filtering activated sludge to find out how internal pressure profiles were changing with time. Based on the pressure profiles, evidences that indicated the local flux near membrane exit was lower than those in adjacent area were found. This observation contradicted to the filtration models based on critical flux concept. It was considered that the cake layer collapse near the membrane exit was the cause. Though there was some degree of delay in pressures detection, the method demonstrated in this study provided a great accuracy when pressure profiles did not change rapidly. 相似文献
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Tarun K. Poddar Sudipto Majumdar Kamalesh K. Sirkar 《Journal of membrane science》1996,120(2):221-237
Atmospheric emission of volatile organic compounds (VOCs) such as toluene, xylene, acetone etc. from industrial facilities causes serious environmental problems and financial losses. Existing technologies for VOC emission abatement have many strengths as well as considerable limitations. A regenerative absorption-based process for removal of VOCs from N2 in an inert, nonvolatile, organic liquid flowing in compact hollow fiber devices has been studied here. These devices eliminate flooding, loading and entrainment encountered in conventional absorption units. Detailed experimental results and theoretical analyses for absorption studies were communicated elsewhere. The overall performance of the combined absorption-stripping process is described here; it appears to be controlled by stripping due to the low temperature and the lower membrane surface area in the stripper. The difference between only absorption and combined absorption-stripping results was more pronounced for VOC-absorbent systems having higher Henry's law constant and diffusivity. A theoretical model has been developed from first principles to simulate the behavior of the membrane stripper; this has been combined with the model for the membrane absorber to determine the overall process performance. Simulated results obtained from the mathematical models agree well with the experimental results for combined absorption-stripping. Simulation results suggest that higher stripping temperature and larger stripper area enhance the performance considerably. 相似文献
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《Journal of membrane science》1999,155(2):291-307
In this paper results obtained with air gap membrane distillation (AGMD) using sucrose aqueous solutions are shown. The role of the relevant process parameters has been investigated experimentally (the flow rate through the cell, the feed initial concentration, the type of membrane, the air gap thickness, etc.). Equations have been proposed to estimate the intermediate temperatures for the air gap configuration. The fluxes given by different gas stagnant film diffusion models showed good agreement with the experimental results over the entire range of temperatures studied. Also a model which accounts for the thermal diffusion phenomenon was used. From the fits of the experimental flux data to the theoretical equations, the diffusion coefficient of the water vapour–air mixture, DAB, and the thermal diffusion coefficient, KT (only in the last case), were obtained and the results were analysed. For the DAB coefficient higher values than the tabulated ones have been obtained, although of the same order of magnitude, and still higher when the thermal diffusion is considered. 相似文献
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《Journal of membrane science》1997,128(2):141-149
By the incorporation of filler materials in a membrane one may change the permeability of the overall, dense membrane towards various gases, vapours and/or liquids. The influence of solid fillers dispersed in a polymeric matrix on permeability, diffusivity and solubility has been studied extensively in literature. In this paper the influence of the filler on overall membrane permeability resulting in an upper and a lower limit of the permeability given the filler content and the permeability of the continuous phase will be studied theoretically. From this analysis the change in membrane selectivity towards a gas mixture by incorporation of a filler, relative to the selectivity of the pure matrix membrane, can be obtained. The maximum change in membrane selectivity is a function of the filler content only, i.e. irrespective of matrix and filler permeabilities. The difficulties often encountered in estimating the filler permeability from experimental permeability data using membranes with varying amounts of the filler will be discussed, and possible solutions will be given using theoretical and experimental data. 相似文献
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A vacuum membrane distillation (VMD) model has been developed and validated with experimental data. The model consists of an extended transport model for the VMD process and is able to predict the effects of concentration and temperature polarization on the overall process performance. To validate the model, first it was tested with few experimental case studies from literature [S. Bandini, G.G. Sarti, Heat and mass transport resistances in vacuum membrane distillation per drop, AIChE J. 45 (7) (1999) 1422–1433; K.W. Lawson, D.R. Lloyd, Membrane distillation. I. Module design and performance evaluation using vacuum membrane distillation, J. Membr. Sci. 120 (1996) 111–121; A.M. Urtiaga, G. Ruiz, I. Ortiz, Kinetic analysis of the vacuum membrane distillation of chloroform from aqueous solutions, J. Membr. Sci. 165 (2000) 99–110]. Then the VMD model has been validated with experimental data collected from the recovery of aroma compounds from black currant [R.B. Jørgensen, A.S. Meyer, C. Varming, G. Jonsson, Recovery of volatile aroma compounds from black currant juice by vacuum membrane distillation, J. Food Eng. 64 (2004) 23–31]. In this work, recovery of 12 characteristic volatile aroma compounds from black currant juice has been studied. The simulated results from the VMD model, in terms of aroma concentration in the permeate have been compared with those obtained from laboratory experiments. The validated model has been used to study the effects of various process and membrane parameters on the concentration factor. The physical properties of various aroma compounds have been predicted using group contribution method as a function of temperature. 相似文献
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Theoretical modeling and experimental analysis of direct contact membrane distillation 总被引:1,自引:0,他引:1
A two-dimensional mathematical model was theoretically developed to predict the temperature polarization profile of direct contact membrane distillation (DCMD) processes. A concurrent flat-plate device was designed to verify the theoretical prediction of pure water productivity on saline water desalination. The numerical results from the temperature polarization profile were obtained using the finite difference technique to reduce the two-dimensional partial differential equations into an ordinary differential equations system. The resultant simultaneous linear equations system was solved with the fourth-order Runge-Kutta method. The results show theoretical prediction agreement with the measured values from the experimental runs. A combination of the Knudsen flow and Poiseuille flow models in the present mathematical formulation for membrane coefficient estimation was used to establish theoretical agreement. The influence of the inlet saline water temperature and volumetric flow rate on the pure water productivity as well as the hydraulic dissipated energy are also delineated. 相似文献
9.
Supersonic expansion is a very powerful tool to produce an atomic beam with a well defined velocity and, by seeding a test gas in such an expansion, the energy of the test gas can be transferred, at least partially, to the very-low-temperature carrier gas. The case usually studied is the one of a heavy gas seeded in a light carrier gas and, in this case, the parallel temperature of the seeded gas is always larger than the one of the carrier gas. In the present paper, we study the opposite case which has received less attention: when a light gas is seeded in a heavier carrier gas, the parallel temperature can be substantially lower for the seeded gas than for the carrier gas. This effect has been first observed by Campargue and co-workers in 2000, in the case of atomic oxygen seeded in argon. In the present paper, we develop a theoretical analysis of this effect, in the high dilution limit, and we compare our theoretical results to several experimental observations, including a set of measurements we have made on a beam of lithium seeded in argon. The agreement between theory and experiments is good. 相似文献
10.
Recently, the EDTA-based sweeping of metal ion that combines chelate formation and in-line sample pre-concentration was advanced. However, the moving chelation boundary (MCB) existing in the sweeping system has not been investigated for the quantitative illumination of the mechanism of metal ion sweeping yet. In this paper, the model of MCB was developed from the EDTA-based sweeping. The theoretical studies were performed for boundary movements and controllable sweeping of metal ion. The theoretical studies show that the sweeping system contains the MCB boundary and chelate boundary, and the difference between the MCB and chelate boundary velocities plays a key role in the stacking efficiency of metal ion. To demonstrate the validity of the theoretical conclusion, the experiments of continuous EDTA-based sweeping were performed with CE and a home-made apparatus of a large tube. The home-made apparatus consisted of a glass tube used for the run of continuous EDTA-based sweeping and two peristaltic pumps used for the supply of solution. The experimental results were in accordance with the theoretical conclusions above. The developed theory holds evident for significance for the mechanism of controllable stacking of metal ions in EDTA-based sweeping system in CE. 相似文献
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A new computational approach to calculating binding energies and spatial positions of small molecules, peptides, and proteins in the lipid bilayer has been developed. The method combines an anisotropic solvent representation of the lipid bilayer and universal solvation model, which predicts transfer energies of molecules from water to an arbitrary medium with defined polarity properties. The universal solvation model accounts for hydrophobic, van der Waals, hydrogen-bonding, and electrostatic solute-solvent interactions. The lipid bilayer is represented as a fluid anisotropic environment described by profiles of dielectric constant (ε), solvatochromic dipolarity parameter (π*), and hydrogen bonding acidity and basicity parameters (α and β). The polarity profiles were calculated using published distributions of quasi-molecular segments of lipids determined by neutron and X-ray scattering for DOPC bilayer and spin-labeling data that define concentration of water in the lipid acyl chain region. The model also accounts for the preferential solvation of charges and polar groups by water and includes the effect of the hydrophobic mismatch for transmembrane proteins. The method was tested on calculations of binding energies and preferential positions in membranes for small-molecules, peptides and peripheral membrane proteins that have been experimentally studied. The new theoretical approach was implemented in a new version (2.0) of our PPM program and applied for the large-scale calculations of spatial positions in membranes of more than 1000 peripheral and integral proteins. The results of calculations are deposited in the updated OPM database ( http://opm.phar.umich.edu ). 相似文献
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Takashi Iwatsubo Toshio Masuoka Kensaku Mizoguchi 《Journal of Polymer Science.Polymer Physics》1994,32(1):1-6
Pervaporation of a water/alcohol mixture through a membrane which has ion-exchange capacity has been investigated. Theoretical equations are introduced which relate the degree of ionic dissociation of the polymer to quantities of water and alcohol dissolved in the polymer. From these equations, an equation for selective dissolution R is derived which does not contain an explicit term for ionic dissociation. Dissociation affects selective dissolution only by changing the degree of swelling of the polymer. Reformulating R asymptotically obtains a reciprocal relationship between permselectivity and permeability for a water-selective membrane. Experiments to check the validity of the relationship have been carried out using chitosan membranes neutralized by several acids. The effect of degree of neutralization also has been investigated. Results can be well understood on the supposition that ionic dissociation depends upon the water/alcohol composition, the kind of acid, and the degree of neutralization. Experimental results indicate that the reciprocal relationship is maintained over an appropriate range of feed compositions which confirm the validity of the theoretical equations for the swelling equilibrium of an ionic membrane. © 1994 John Wiley & Sons, Inc. 相似文献
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真空注浆法制备YSZ电解质膜管及其在固体氧化物燃料电池中的应用 总被引:7,自引:0,他引:7
以吡啶为分散剂,采用真空注浆法制备出膜厚为0.2mm、长度为140mm的致密YSZ电解质膜管。研究了烧结温度对样品致密度和离子导电率的影响.用1650℃烧结2h制备的致密YSZ电解质膜管组装成固体氧化物燃料电池,以氢气和煤气为燃料,研究了电池在500~900℃的电化学性能.实验结果表明,用真空注浆法可制备出高质量和高密度的YSZ电解质膜管,在1600℃烧结后,其相对密度已达到理论密度的98.1%,接近理论密度.单电池的开路电压最大值为1.213V,最大输出功率为0.48W.以氢气为燃料的燃料电池性能明显高于以煤气为燃料的电池性能. 相似文献
16.
A theoretical model has been developed that describes ultrafiltration of nonionic surfactants. The model takes into account the fact that surfactants start to aggregate and form micelles at the critical micelle concentration. The model can be used to predict the performance of the membrane if the transport properties inside and at the membrane surface as well as the surfactant association behavior, are known. Three hydrophilic ultrafiltration membranes, made of regenerated cellulose, were used in the investigation. The cut-offs of the membranes were 10,000, 20,000, and 30,000 Da. The surfactant used in the investigation was the nonionic surfactant Triton X-100. The influence of the concentration of surfactant, transmembrane pressure and pure water flux were studied theoretically and experimentally. From the results presented in this work it can be concluded that the calculated values are in good agreement with experimental data. 相似文献
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湿润率对疏水性膜接触器传质性能的影响 总被引:2,自引:0,他引:2
根据双膜理论提出了疏水性膜湿润机理,关联了阻力层方程、Laplace方程和膜孔径分布函数,建立了新型传质数学模型,采用PP疏水性微孔膜、水和MDEA(N-甲基二乙醇胺)水溶液为吸收剂,研究了膜接触器吸收CO2传质过程,考察了压差、表面张力和温度等因素所产生的湿润率对传质性能的影响.结果表明,用新型模型能较准确地预测湿润率对传质系数的影响,模型值与实验值符合较好;压差、表面张力和温度对湿润率影响较大,是膜接触器传质过程需要考虑的因素. 相似文献
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Summary Sorbtion of cobalt halide species on an anion exchange membrane has been studied by spectral measurements in the u.v., visible and far i.r. region. The results obtained were compared with parameters calculated for mixed water halide species. From this data, the predominant species sorbed from various solutions and their geometry have been defined. 相似文献