Measurements and predictive modeling of water diffusion coefficients in bovine serum albumin/polymer blends for biosensors

The knowledge of mass transport parameters in polymer/protein blend films is of substantial interest for the preparation of glucose biosensor test strips where drying and rehydration need to be controlled. In this study, the diffusion of water in bovine serum albumin (BSA) and poly(vinylpyrrolidone) (PVP) films and blends of BSA with PVP and polyvinylalcohol is investigated and the applicability of predictive models for the diffusion coefficient in mixtures is explored. Water concentration profiles are measured with Raman spectroscopy during drying experiments under controlled conditions. Concentration‐dependent diffusion coefficients of water in the films are then determined by fitting simulated drying curves to measured data. Comparison of the resulting diffusion coefficients in the blends with a predictive logarithmic model shows good agreement. The application of such predictive models could greatly facilitate the development of polymer/protein blends in the future. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45368.     

Characterization of isotherms and thin-layer drying of red kidney beans,Part II: Three-dimensional finite element models to estimate transient mass and heat transfer coefficients and water diffusivity

Three-dimensional finite element models with consideration of shrinkage and irregular shape were developed to estimate the relationships among the transient heat and mass transfer coefficients, the transient water diffusivity, and the temperature and moisture content of the red kidney beans being dried under different drying conditions. An equation was developed to calculate the transient mass transfer coefficient using the measured time–moisture content data. This calculated transient mass transfer coefficient was further used to calculate the transient heat transfer coefficient. To verify the predicted temperature on the surface of the red kidney beans, surface temperature was measured using a handhold infrared thermometer. These measured temperature and time–moisture content data were used to determine the transient water diffusivity using the least square method when the red kidney bean kernel experienced a shrinkage during drying. Strong relationship among the transient heat and mass transfer coefficients, the water diffusivity, and the ratio of the transient heat and mass transfer coefficients was revealed. This relationship could be used to predict temperature and moisture content of the red kidney beans during the entire drying period. The Lewis number?=?27, and the ratio of the transient heat over mass transfer coefficients was 10765?J?m^?3?k^?1 at 30 and 40°C, and 10729?J?m^?3?k^?1 at 50°C. Shrinkage did not significantly influence the value of the estimated transient water diffusivity.     

电渗析过程传质模型的研究进展

电渗析是一种利用离子交换膜和电势差从溶液及其他不带电组分中分离出离子的物质分离过程,该技术具有适应性强、预处理简单、能耗低、环境污染小等优点,被广泛应用于化工、生物等领域的分离纯化过程。本文主要介绍了用于电渗析分离过程的6种传质模型,总结了各模型的优势及存在的问题,指出限制电渗析技术进一步发展的主要原因是对包含物质传递、浓差极化、流体流动行为、电解质溶液-膜平衡等复杂现象的电渗析过程进行理论和实验研究难度大,而传质模型化为电渗析分离过程的物质传递研究提供了一条有效途径,有助于深入研究电渗析过程中物质的传递机理,准确预测分离性能并导向性优化电渗析结构设计和操作工艺。并且提出未来电渗析传质模型的研究方向是结合经验方程或传质系数进一步优化传质模型,并采用仿真工具模拟传质过程,提高模型的准确性和普适性。     

PREDICTION OF MASS TRANSFER COEFFICIENTS IN REGULAR PACKED COLUMNS

Developments in the area of packed columns, particularly structured packed columns, are ongoing, specifically in the area of liquid-liquid extractions. Accurate predictions of mass transfer coefficients lead to more accurate design of columns. In the present study, mass transfer coefficients were measured experimentally for packed columns of different heights to study the effect of packing height and specific area. Two experimental pilot regular packed extraction columns were examined using toluene/acetic acid/water and n-butyl acetate/acetic acid/water systems. Based on the results, a novel model for prediction of effective diffusivity has been proposed that is a function of column height and specific area. The mass transfer coefficients obtained by this prediction were compared with other models. The results of this new model are in good agreement with the experimental data. Therefore, this new model can be used to design better regular packed columns.     

Vapour- and liquid-side volumetric mass transfer coefficients measured in distillation column. Comparison with data calculated from absorption correlations

Volumetric mass transfer coefficients in liquid and vapour phases in distillation column were measured by the method consisting of a fitting of the concentration profile of liquid phase along the column obtained by the integration of a differential model to the experimental one. The mathematical model of distillation process includes mass and energy balances and the heat and mass transfer equations. The film model flux expressions with the convective transport contributions have been considered in the transfer equations. Vapour and liquid phases are supposed to be at their saturated temperatures along the column. Effect of changes of phase flows and physical properties of phases on the mass transfer coefficients along the column and non-ideal thermodynamic behaviour of the liquid phase have been taken into account. The concentration profiles of liquid phase are measured in the binary distillation of the ethanol-water and methanol-ethanol systems at total reflux on metal Pall Rings and Intalox saddles 25 mm in the column with diameter of 150 mm. The distillation mass transfer coefficients obtained by the fitting procedure are compared with those calculated from absorption data using Onda's, Billet's and Linek's correlations. The distillation heat transfer coefficients calculated from the model assuming saturated temperatures in both phases are compared with those calculated from the Chilton-Colburn and penetration model analogy between mass and heat transfer. The results have confirmed an agreement neither between distillation and from absorption correlations calculated mass transfer coefficients nor between analogy and from enthalpy balance calculated heat transfer coefficients. Also the concentration profiles obtained by the integration of the differential model of the distillation column using the coefficients from absorption correlation have differed from the experimental profiles considerably.     

不同分子模型对甲烷水合物分解微观特性表征

采用SPC/E-UA、SPC/E-AA、TIP4P-UA和TIP4P-AA分子模型研究了NVE系综下甲烷水合物的微观分解特性。对比分析了不同模型下水合物的平衡温度及分解热。研究了F₃随空间及时间的变化,对液态水-水合物的界面进行了界定。比较了不同区域的势能的变化规律,发现分解过程具有显著的非平衡传热特性。分析了水和甲烷密度的空间分布规律及逸出的甲烷分子数随时间的变化规律,发现甲烷逸出速度逐渐减小。对不同模型下分解所需的活化能进行了计算,并与实验值进行对比。对比不同区域均方位移及扩散系数发现分解呈现显著的非平衡传质特性。研究表明甲烷分子模型对分解影响甚微,而水分子模型影响较为明显,在NVE系综下通过SPC/E模型表征的平衡温度、活化能及分解热与实验值更加吻合。     

采用泰勒分散法测量蜡分子扩散系数

蜡分子扩散系数是蜡沉积预测模型中非常重要的物性参数。为测量蜡分子（高碳数正构烷烃）在液相体系中的分子扩散系数,建立了基于泰勒分散法的扩散系数测量装置,并对装置操作注意事项进行了详细探讨。采用该装置测量了丙酮水溶液、n-C₆+n-C₇溶液以及甲醇水溶液中溶质在溶剂中的分子扩散系数,以文献值对测量值进行校验,验证了装置的可靠性。分别以n-C₁₈、n-C₂₀、n-C₂₂、n-C₂₄、n-C₂₆为溶质,以n-C₇为溶剂,在不同温度、浓度下测量蜡分子在液相体系中的分子扩散系数,并将实验测量值与Hayduck-Minhas关系式计算值进行比较。结果表明：蜡分子扩散系数随温度升高而线性增大,随溶液中蜡分子摩尔分数的增大而以指数形式减小;在相同条件下,高碳数正构烷烃的分子扩散系数低于低碳数正构烷烃的分子扩散系数。采用Hayduck-Minhas关系式的计算结果比实验测量结果平均小50%,应用于蜡沉积预测时,将低估蜡分子扩散质量流。     

Mixing of two binary nonequilibrium phases in one dimension

The mixing of nonequilibrium phases has important applications in improved oil recovery and geological CO₂‐storage. The rate of mixing is often controlled by diffusion and modeling requires diffusion coefficients at subsurface temperature and pressure. High‐pressure diffusion coefficients are commonly inferred from changes in bulk properties as two phases equilibrate in a PVT cell. However, models relating measured quantities to diffusion coefficients usually ignore convective mass transport. This work presents a comprehensive model of mixing of two nonequilibrium binary phases in one‐dimension. Mass transport due to bulk velocity triggered by compressibility and nonideality is taken into account. Ignoring this phenomenon violates local mass balance and does not allow for changes in phase volumes. Simulations of two PVT cell experiments show that models ignoring bulk velocity may significantly overestimate the diffusion coefficients. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Incorporation of osmotic pressure in an integrated incremental model for predicting RO or NF permeate concentration

Consideration of concentration, recovery and osmotic pressure has been incorporated in a fully integrated diffusion based mass transfer model identified as integrated osmotic pressure model (IOPM). Osmotic pressure was incorporated into the model using correction coefficients that were calculated from boundary conditions, which were determined from the feed and concentrate streams osmotic pressures. Predicted permeate stream water quality using IOPM and the homogenous solution diffusion model (HSDM) were compared with and without consideration of osmotic pressure. IOPM was verified using independently developed data from full and pilot scale plants. The numerical simulation and statistical assessment show that osmotic pressure corrected models are superior to non-osmotic pressure corrected models, and that IOPM improved predictability of permeate stream water quality.     

SURFACE MASS TRANSFER COEFFICIENTS FOR WOOD

Experimentally determined mass transfer coefficients for wood surfaces are often much lower than theoretically and experimentally determined coefficients for other surfaces. An investigation of this is made by comparing mass transfer coefficients for water and saturated non-wood surfaces, with coefficients measured for wood surfaces. It is found that measurements on wood surfaces are usually evaluated by assuming that Fick's law describes diffusion in wood. As this is not always true, it is proposed that the mass transfer coefficients measured on wood surfaces are low because the internal mass transfer in wood is not well understood. New measurements are presented which support this conclusiou.     

Modelling of alcohol and water diffusion in fuel cell membranes—Experimental validation by means of in situ Raman spectroscopy

In this work a multi-component transport model has been set up to describe the diffusion driven mass transport of water and methanol in fuel cell membranes. For a membrane in contact with liquid methanol and water on one side and conditioned air on the other, the corresponding differential equations and boundary conditions were derived in a polymer-related coordinate system taking into account the polymers three-dimensional swelling. Phase equilibrium parameters and unknown diffusion coefficients for Nafion^® 117 were obtained by comparing the simulation results to water and methanol concentration profiles measured with confocal Raman spectroscopy. The influence of methanol concentration, temperature and air flow rate was predicted by the model with a maximum relative mean deviation between measurement and simulation of 8.6% for methanol and 3.4% for water.     

Turbulent particle mass flux in a two-phase shear flow

This paper presents measurements of mean and rms of fluctuations of concentration, particle turbulent velocities, shear stress and covariance of the fluctuations of particle number density and particle velocities in a horizontal plane shear layer. Particle Image Velocimetry (PIV) was used to obtain simultaneously particle velocities and number densities to evaluate models for the prediction of particle dispersion in Reynolds-Averaged Navier-Stokes calculation approaches. The flow was horizontal with the low speed side on top and laden with nearly mono-dispersed 55 and 90 µm glass beads, which were injected at the upper, low speed side of the flow. The Stokes number of the particles was in the range of 0.41 to 4.3 and the drift parameter due to gravity was in the range 0.18 to 1.5. The experimental results quantified how particle ‘centrifuging’ by the large fluid vortices influenced the measured quantities. The turbulent particle mass flux was compared with models based on the gradient of mean particle concentration. Different dispersion coefficients were evaluated by introducing the measured quantities into the model equation and it was found that dispersion coefficients based on the fluid eddy diffusivity performed poorly leading to an order of magnitude errors. A dispersion coefficient in tensor form, based on the product of particle shear stress and particle integral time scale, led to good agreement with measured turbulent particle mass fluxes with errors between 0 and 50%.     

Interpretation of mass transfer measurements in bubble columns considering dispersion of both phases

Mass transfer measurements in two bubble columns with an inner diameter of 100 resp. 140 mm with the systems air/water/carbon dioxide and nitrogen/n-propanol/carbon dioxide have been evaluated with the axial dispersion model. The dispersion coefficients of both phases have been determined in separate investigations. As the results revealed a strong influence of the liquid viscosity, additional dispersion coefficient measurements have been carried out with the system air/glycol. It could be shown that the liquid phase dispersion coefficient decreases with increasing viscosity while the gas phase dispersion coefficient increases with increasing liquid viscosity. Both coefficients are strongly dependent on the gas throughput and the column diameter. Using these coefficients, the mass transfer coefficients have been calculated by fitting the calculated concentration profile to the measured values and by splitting the volumetric mass transfer coefficient with the experimental value of the interfacial are a. The results agree best with a correlation of Calderbank and Moo-Young.     

On the concentration dependence of the UNIQUAC/UNIFAC models

The UNIQUAC/UNIFAC models can not in general represent vapor-liquid and liquid-liquid equilibria simultaneously with satisfactory results. Recent modifications of the models take into account association and solvation effects by means of chemical theory. However, this approach leads to complicated expressions for the activity coefficients and the improvements are only moderate. A modification of the UNIQUAC/UNIFAC models is presented which takes into account solvation and association by allowing the interaction energies to vary with composition. This approach leads to explicit expressions for the activity coefficients. It is shown that the modified models in simultaneous correlations lead to quantitative representation of vapor-liquid equilibrium data and semi-quantitative representation of binary and ternary liquid-liquid equilibrium data.     

基于电荷模型的荷电膜传递现象的研究进展

根据电荷模型（空间电荷和固定电荷模型）,将荷电膜传递现象分为膜的分离性能、电性质及传递参数3类.其中膜的分离性能用截留率和通量来表征;膜的电性质包括膜的电化学性质和膜的动电性质,膜的电化学性质用膜电位来表征,膜的动电性质用流动电位、Zeta电位和电滞效应等参数来表征;膜的传递参数则用反射系数、溶质透过系数、纯水透过系数、电导率、离子的迁移数及电渗系数6个系数来表征.概述了空间电荷和固定电荷模型描述电解质溶液在荷电膜中的传递现象的研究进展,介绍了两种模型在荷电膜中应用时的各自优势,展望了电荷模型在荷电膜体系中应用的发展方向.     

Prediction of Concentration Profiles in an L‐Shaped Pulsed Extraction Column

The L‐shaped extraction pulsed plate column is believed to be able to perform under operating conditions between those of the vertical and the horizontal pulsed plate columns. It has an extraction efficiency similar to the vertical pulsed plate column. Here, the mass transfer performance of this novel column type was investigated and the application of three different models, i.e., the plug flow, the axial dispersion, and the back flow models, was evaluated to predict the solute concentration profile along the column length. The water‐acetone‐n‐butyl acetate and the water‐acetone‐toluene systems were used. The influence of the operational parameters on the height of the mass transfer unit and the back flow coefficients was evaluated using the back flow model. New correlations were proposed to predict the height of the mass transfer unit along with the back flow coefficients in each phase, which were in satisfactory agreement with the experimental data.     

Probing Water Diffusion Inside Crystals of AlPO-5 by PFG NMR and IRM for Heat Storage Applications

Diffusion of water in the aluminophosphates AlPO-5 is studied using a combination of pulsed field gradient NMR and IR microimaging. The concentration profiles measured by the latter allowed to visualize the process of water sorption and propagation into the crystals of AlPO-5. The self-diffusion coefficients obtained by NMR were one order of magnitude higher values compared to corrected ones from the IR microimaging study. The concentration profiles allowed to visualize the process of water sorption and propagation into the crystals of AlPO-5. The obtained results are compared with experimental and simulation data for the water/AlPO-5 system for the literature and discussed in the context of its potential use for heat storage applications.     

SURFACE MASS TRANSFER COEFFICIENTS FOR WOOD

ABSTRACT

Experimentally determined mass transfer coefficients for wood surfaces are often much lower than theoretically and experimentally determined coefficients for other surfaces. An investigation of this is made by comparing mass transfer coefficients for water and saturated non-wood surfaces, with coefficients measured for wood surfaces. It is found that measurements on wood surfaces are usually evaluated by assuming that Fick's law describes diffusion in wood. As this is not always true, it is proposed that the mass transfer coefficients measured on wood surfaces are low because the internal mass transfer in wood is not well understood. New measurements are presented which support this conclusiou.     

Removal of acetic acid from water by catalytic distillation. Part 2: Modeling and simulation studies

A simulation program has been established by incorporating basic models for reaction kinetics, vapor–liquid equilibrium and mass transfer into Aspen Plus (Aspen Technology Inc., 1996) to simulate the catalytic distillation process for the removal of dilute acetic acid from water. The simulated concentration profiles agree well with those measured under various operating conditions.     

Soft-sensor models to estimate the efficiency of H2S removal from an oil refinery stream of nonphenolic sour water

A large set of results of concentration of hydrogen sulfide in the feed and bottom product streams of a sour water stripper found in a typical oil refinery was experimentally obtained. The readings of H₂S concentrations were at several different operating conditions in terms of the main process variables that classically have significant effects on the efficiency of H₂S removal (E). In particular, the considered factors were the mass flow rate, and temperature of sour water fed into the stripper, the mass flow rate of external steam injected into the reboiler, the difference between the temperature of the product stream leaving and entering the reboiler, and the difference of pressure at the two ends of the tower. Three different soft-sensor models were suggested to describe the observed variation in E from 63 to 97%, namely, an equilibrium, statistical and an artificial neural network model. The best of them was the neural network one with three input variables, four neurons in the one-hidden layer, and a hyperbolic tangent function for both the output and one-hidden layers. The mean absolute relative deviation between measured and calculated E by involving this model was only approximately 2.5% with negligible tendency for the residuals. It confirms the reliability of this approach as a tool to inferential estimation of the efficiency of removal of H₂S from the sour water by stripping.