On the combination of different transport mechanisms for the simulation of steady-state mass transfer through composite systems using permeation through stainless steel supported silicalite-1 membranes as a model system

A method to calculate the steady-state multicomponent mass transfer in heterogeneous structures is presented. For this, different transport mechanisms represent different regions inside the composite system. The solving scheme allows the calculation of the molar flow rates along the different transport pathways and the estimation of unknown transport parameters based on experimental data.

The steady-state mass transfer of hydrogen and sulfur hexafluoride through a sinter metal supported MFI zeolite membrane is examined as a model system. The support is simulated using the dusty gas model, the molecules passing the zeolite layer may follow transport mechanisms like Knudsen diffusion, surface diffusion or activated gas diffusion. The configuration used, with data from single gas experiments, can predict the binary system only at high temperatures. The problems arising at low temperatures are due to the oversimplified assumption that adsorbed and desorbed molecules do not interact on their way through the MFI zeolite micropores.

However, because of the modular structure of the approach, it can be easily extended to more advanced transport models to account for interactions between the different molecules. And the method can be applied equally well to other systems, such as palladium composite membranes or membranes with catalytic activity.     

几何结构对滤压式电解槽内部传质的影响

Effect of configuration （structure of electrode, interelectrode gap, positions of inlet and outlet, volume of the cell and additional nets） on mass transfer characteristic of a filter-press type electrochemical cell has been studied. The mass transfer coefficients on the electrodes were obtained by using the well-known technique based on the determination of limiting diffusion current. It is found that mass transfer coefficients with mesh electrode are greater than that of with plate electrode. Mass transfer coefficient is decreased with interelectrode gap. While interelectrode gap achieved a certain value （7 ram）, mass transfer coefficient is steady, no more declining. Mass transfer characteristic for different positions of inlet and outlet are different and dimensionless number groups correlated equations are obtained by experiment. Mass transfer characteristic is the best when inlet located on the top and outlet on the bottom of the cell respectively. While magnified the volume of the cell to eight times, mass transfer characteristic changes little. Mass transfer characteristic without nets is lower than that of with additional nets in the exit region, but higher than that of with additional nets in the entry region.     

A novel transport model for sorption and desorption of penetrants in dense polymeric membranes

The transport of penetrants in polymeric membranes is assumed to be a process of mixing of penetrant and polymer molecules, in which a creep strain is induced concurrently. Based on the assumption and combined with the mass conservation equation and phenomenological diffusive flux expression, a new transport model of penetrant in polymeric membrane is established, in which the total change of excess Gibbs free energy is considered as a sum of three parts calculated by the modified Scatchard-Hildebrand model, Flory-Huggins theory and linear viscoelastic theory, respectively. The partial difference equations in the model are solved by implicit finite difference method of Crank-Nicolson form, and the model parameters are optimized by simplex algorithm. The model is used to calculate various diffusions (Fickian diffusion, and non-Fickian diffusion) of ethanol in polyphthalazine ether sulfone (PPES), and polyphthalazine ether sulfone ketone (PPESK) membranes at 293.15, 298.15, and 303.15 K. The calculated results are in agreement with the experimental data and the maximal relative deviation is no more than 10.54% and the average relative deviation is 4.35%.     

A dynamic model of the fuel processor for a residential PEM fuel cell energy system

A dynamic numerical model describing an experimental methane fuel processor for a residential PEMFC energy system is presented. In contrast to previous simulation studies of steam reforming of methane, this model includes the various energetic couplings due to spatial proximity and constructive layout of the components. Thus, all significant energy flows inside the system are taken into account, including those caused by unintended conduction and radiation. Steady-state simulations were carried out to investigate the effect of a constructional modification in the reformer, which clearly reveal the significant influence of thermal couplings on the reformer efficiency. Furthermore, dynamic simulations were performed for the start-up procedure of the fuel processor and compared to experimental data. The results demonstrate that the dynamic model is a useful tool for further investigations of unsteady operating conditions and for optimisation with respect to both construction and system operation.     

Semi-empirical model of toluene transport in polyethylene membranes based on the data using a new type of apparatus for determining gas permeability, diffusivity and solubility

Solubility, diffusivity and permeability of toluene vapors in low-density polyethylene (LDPE) membranes of various thicknesses (approximately 48, 93, 138 and 187 μm) at different temperatures 30, 40 and 50 °C in the range of relative vapor pressure p/p⁰=(0.05; 0.95) were measured using new type of permeation apparatus. Moreover, special construction of the new cell enables determination of the permeant amount sorbed in the membrane in the steady state operation of vapor permeation.The simple semi-empirical model of toluene transport in a polyethylene membrane based on relation between experimentally obtained effective diffusion coefficients and concentration dependent diffusion coefficients evaluated from experiments on a new permeation apparatus was proposed. The model enables estimation of toluene fluxes, sorption in the steady state of vapor permeation and concentration profiles in a polyethylene membrane from equilibrium sorption isotherms and effective diffusion coefficients. Very good agreement between experimental and calculated values from the proposed model was obtained.     

Water sorption and diffusional properties of a cured epoxy resin measured using alternating ionic liquids/aqueous electrolytes in electrochemical impedance spectroscopy

The protective quality of a coating is often measured by how long it delays the arrival of water to the substrate. The transport of water in, redistribution within, and eventually through a coating to the substrate has long been investigated through electrochemical impedance spectroscopy (EIS). EIS measurements employing alternating nonaqueous (room temperature ionic liquids, RTIL) and aqueous electrolytes elucidated the behavior of water within the coating. Diffusion coefficients could be measured and the redistribution of water into percolating paths identified. The use of RTIL alternating with aqueous electrolytes allows determination of intrinsic properties (water volume fraction at saturation and relative dielectric) and kinetic properties predicted by the Brasher Kingsbury formulation. This article focuses on the sensitivity of these intrinsic and kinetic properties to test duration in an unique experimental method.     

Numerical simulation of mass transport in a filter press type electrochemical reactor FM01-LC: Comparison of predicted and experimental mass transfer coefficient

This paper studies flow characteristics and their effect on local mass transfer rate to a flat plate electrode in a FM01-LC electrochemical reactor. 3D reactor simulations under limiting current and turbulent flow conditions were performed using potassium ferro-ferricyanide electrochemical system with sodium sulfate as supporting electrolyte. The model consists of mass-transport equations coupled to hydrodynamic solution obtained from Reynolds-averaged Navier–Stokes equations using standard k–? turbulence model, where the average velocity field, the turbulence level given by the eddy kinetic energy and the turbulent viscosity of the hydrodynamic calculation were used to evaluate the convection, turbulent diffusion and the concentration wall function. The turbulent mass diffusivity was evaluated by Kays–Crawford equation using heat and mass transfer analogies, while wall functions, for mass transport, were adapted from Launder–Spalding equations. Simulation results describe main flow properties, concentration profiles throughout the entire volume of the reactor and local diffusion flux over the electrode. Overall mass transfer coefficients estimated by simulation, without fitting parameters, agree closely with experimental coefficients determined from limiting current measurements (1.85% average error) for Re between 187 and 1407.     

Liquid membranes a moving film apparatus for measurement of mass transfer in emulsions,and its application to active transport of phosphate ions

A new apparatus to measure mass transfer in emulsion is described. It consists in a cylindrical rod of “Teflon” surrounded by a flowing film of a water-in-oil emulsion in a column filled with an aqueous solution. It allows easy and precise measurement of the interfacial area between the solution and the emulsion. In the conditions of the experiments, mass transfer resistance can be assumed to be mainly in a diffusional layer of the organic phase of the emulsion.Data of the rate of active transport of phosphate ions through the organic phase of a water-in-oil emulsion using Aliquat 336 as carrier and montanide 80 as surfactant are obtained.A simple diffusion model, assuming fast exchange reaction at the interfaces and control of the kinetics by the diffusion through a very thin layer of the organic phase, gives a good representation of the kinetics of transfer and explains its dependence on carrier and surfactant concentrations in good agreement with experimental results.     

An empirical model for kinetics of boron removal from boroncontaining wastewaters by the electrocoagulation method in a batch reactor

Boron removal from boron containing wastewaters prepared synthetically via the electrocoagulation method was studied. The experiments in which aluminum plate electrode was used were carried out in a batch reactor. The solution pH, initial boron concentration, current density, type of supporting electrolyte, temperature of solution and stirring speed were selected as experimental parameters. The obtained experimental results showed that efficiency of boron removal increased with increasing current density and decreased with increasing boron concentration in the solution. Supporting electrolyte had not significant effects on the percent of total boron removal. pH was very important parameter effecting boron removal and optimum pH was determined to be 8.0. This pH value reached an agreement with activity-pH diagrams for Al⁺³ species in equilibrium with Al(OH)₃ and boron species in aqueous media. As a result of increasing interaction between boron ions and dissolved aluminum ions in solution, the increasing solution temperature increased boron removal efficiency. Increasing stirring speed decreased boron removal efficiency where the increasing stirring speed decreased the capability of floc formation of aluminum ions. As a result, it was seen that about 99% of boron in the wastewater could be removed at optimum conditions. In addition, the process kinetics was predicted by using heterogeneous fluid–solid reaction models. It was seen statistically that the kinetics of this process agreed with the pseudo-second-order model as follows: X_B/(l−X_B) = 18,241[OH][C]^−3.45[CD]^7.79[t]^1.41[S]^−3.65exp[−30,668/RT].     

A model for mass transport in the electrolyte membrane of a DMFC

A steady state model for multicomponent mass transport was derived for the direct methanol fuel cell membrane. Data for development and validation of the model was taken both from experiments and literature. The experimental data was collected in a polarisation cell, where mass transport of methanol across the electrolyte membrane was measured through a potentiostatic method. The results from modelling and experiments showed good agreement. The model was capable of describing the non-linear response in mass transport to increased methanol feed concentration. The model also accurately described the change in membrane conductivity with methanol concentration. From the model transport equations, it was also possible to derive some characteristic transport parameters, namely the electro osmotic drag of both water and methanol, diffusive drag of water and methanol, and effective, concentration dependent, diffusion coefficients for methanol and water.     

A model for simultaneous measurement of gas and solid holdups in a bubble column using ultrasonic method

The ultrasonic method developed to measure the dispersed phase holdups in dispersion systems is based on the fact that the velocity of ultrasound in the dispersion is different from that in the liquid. The relationships between velocity differences in the term of transmission time differences of ultrasound and gas holdup in a gas-liquid system and solid holdup in a liquid-solid system were derived. The holdups became linearly dependent on the time differences, which is in agreement with the experimental data. Based on those relations, a model for simultaneous measurement of gas and solid holdups in three-phase systems is proposed. The model permits measurement of the dispersed phase holdups by measuring the transmission time of ultrasound transmitted through the dispersions in two frequencies. It allows investigation of local holdups distributions in a bubble column and in a suspended bubble column.     

A generalized model for the measurement of effective diffusion coefficients of heterovalent ions in ion exchangers by the zero-length column method

A generalized theoretical model for the measurement of effective diffusion coefficients of heterovalent ions in ion exchange resins by the zero-length column method was developed. The model included the resistance to mass transfer both in the particle and in the film and described ion fluxes with Nernst-Planck equations. Equilibria were described using a model based on the mass action law. The values of intraparticle diffusivity of Cu²⁺, Cd²⁺, Zn²⁺, and H⁺ on commercial Amberlite IR-120 were obtained by non-linear regression, these values agree fairly well with data reported previously in literature. The following trend was observed: D_Cu>D_Zn>D_Cd.     

Dynamic behaviour of electrochemical reactors for a step change in inlet concentration under potentiostatic control according to the dispersion model

The dynamic modelling of electrochemical reactors under potentiostatic control is performed according to the dispersion model. The response of the system in concentration and current is discussed for a step change in the inlet concentration in terms of the Peclet number. The stirred tank and plug flow behaviours are analyzed as limiting cases of the dispersion model.     

An electrochemical study of stainless steels and a nickel alloy in a decontamination agent using the potentiodynamic method

Chemical decontamination is accepted as one of the effective methods for decreasing radioactivity from radioactive materials existing in the systems of the nuclear power plants. In chemical decontamination processes, metal oxides dissolve in chelating agents such as oxalic acid and EDTA (Ethylenediaminetetraacetic acid) in the dissolution step for the chemical decontamination process. It is important to investigate corrosion behaviors with respect to decontaminating agents in the development of decontamination process. In this study, the potentiodynamic method was considered among electrochemical methods in order to investigate corrosion behaviors of stainless steels (SS 316, SS 304) and a nickel alloy (Inconel 600). The corrosion behaviors observed in the potentiodynamic results agreed with those of corrosion behaviors observed in the weight loss method, showing that the electrochemical study is a very useful method for estimating corrosion behavior.     

Development of a novel electrochemical immuno-assay using a screen printed electrode for the determination of secretory immunoglobulin A in human sweat

This paper reports on the steps involved in the development of a novel electrochemical immunoassay for secretory immunoglobulin A (sIgA) determinations in human sweat. This novel immunoassay involves an initial step whereby sweat sIgA is adsorbed onto a polyvinylidene fluoride (PVDF) membrane (sweat patch). Following a wash step, a solution containing bovine serum albumin (BSA) is used to block any sites at which non-specific binding might occur. After a second wash step, the PVDF sweat patch is transferred to a second tube to which is added diluent and anti-sIgA antibody conjugated to horseradish peroxidase (HRP). Following an incubation step, an aliquot of supernatant containing unbound antibody is transferred to a well in a 96 well plate format which had been previously coated with sIgA. After a second incubation step and wash step, 3,3′,5,5′-tetramethylbenzidine (TMB) is added to the same well and left to undergo enzymatic oxidation. Finally a screen-printed carbon electrode (SPCE) is inserted into the well and any oxidised TMB is detected by chronoamperometry using an applied potential of +50 mV. The resulting reduction current is then referred to a calibration plot to deduce the unknown sIgA concentration. The optimisation of the steps involved in this assay is described in detail. Some preliminary data is presented on sweat sIgA levels collected from human volunteers who had undergone a controlled exercise regime on a bicycle (Ergociser). To our knowledge this is the first report where a sweat patch and a SPCE have been successfully incorporated into an immunoassay for sIgA.     

Nanostructured CuO thin film electrodes prepared by spray pyrolysis: a simple method for enhancing the electrochemical performance of CuO in lithium cells

Nanostructured CuO thin films were prepared by using a spray pyrolysis method, copper acetate as precursor and stainless steel as substrate. The textural and structural properties of the films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The SEM images revealed thorough coating of the substrate and thickness of 450-1250 nm; the average particle size as determined from the AFM images ranged from 30 to 160 nm. The XRD patterns revealed the formation of CuO alone and the XPS spectra confirmed the presence of Cu²⁺ as the main oxidation state on the surface. The films were tested as electrodes in lithium cells and their electrochemical properties evaluated from galvanostatic and step potential electrochemical spectroscopy (SPES) measurements. The discharge STEP curves exhibited various peaks consistent with the processes CuO ⇔ Cu₂O ⇔ Cu and with decomposition of the electrolyte, a reversible process in the light of the AFM images. The best electrode exhibited capacity values of 625 Ah kg⁻¹ over more than 100 cycles. This value, which involves a CuO ⇔ Cu reversible global reaction, is ca. 50% higher than that reported for bulk CuO. The nanosize of the particles and the good adherence of the active material to the substrate are thought to be the key factors accounting for the enhanced electrochemical activity found.     

Use of axial dispersion model for determination of Sherwood number and mass transfer coefficients in a perforated rotating disc contactor

The mass transfer process in a perforated rotating disk contactor (PRDC) using a toluene-acetone-water system was investigated.The volumetric overall mass transfer coefficients are calculated in a PRDC column.Both mass transfer directions are considered in experiments.The influences of operating variables containing agitation rate,dispersed and continuous phase flow rates and mass transfer in the extraction column are studied.According to obtained results,mass transfer is significantly dependent on agitation rate,while the dispersed and continuous phase flow rates have a minor effect on mass transfer in the extraction column.Furthermore,a novel empirical correlation is developed for prediction of overall continuous phase Sherwood number based on dispersed phase holdup,Reynolds number and mass transfer direction.There has been great agreement between experimental data and predicted values using a proposed correlation for all operating conditions.     

冷态模型系统糖浆溶液模拟PET熔体可行性分析

利用旋转流变仪和毛细管流变仪研究了聚对苯二甲酸乙二醇酯(PET)和糖浆溶液的流变行为及黏弹行为,通过对PET熔体和糖浆溶液在线性粘弹区、本构方程、维森伯格(Wi)数及挤出胀大等方面的分析,研究了冷态模型系统中模拟介质糖浆溶液模拟PET熔体的可行性。结果表明:PET的线性粘弹区和糖浆溶液相似,且应力临界值(τc)大于等于1 000 Pa;通过调节糖浆溶液的含水量使之与某一温度下的PET熔体在一定剪切速率范围内具备大概一致的流动曲线,在牛顿流体拟合和Cross拟合范围上,两者具有高度相似性;在储能模量、损耗模量、Wi数及挤出胀大比等方面,PET熔体和经过调节的糖浆溶液具有一定的规律相似性;可通过除去水分、添加一定量的聚丙烯酰胺使糖浆溶液的黏度和弹性在一定的剪切速率范围内与PET熔体具备一致或者相似的变化规律;证实了糖浆溶液作为冷态模型系统模拟介质的可行性。