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In this study, in order to investigate the effect of the underlying pore-scale processes on continuum scale simulations of porous media dissolution, we improve the standard Lattice Boltzmann method using Quadtree grid refinement approach to simulate fluid flow and reactive transport through large domain sizes. Our results have shown considerable computational improvements up to 80% in simulation time together with increased numerical accuracy. The results and the added value of the new approach are discussed using comparison of our model with the conventional LBM. Moreover, we have applied a systematic analysis by increasing complexity levels and starting from fluid flow and continuing with tracer transport and reactive transport in single pores, and ultimately, reactive transport in dissolving porous structures. For each case, the accuracy and computational benefits of the Quadtree models are discussed and dimensionless numbers are used to characterize regimes of flow and reaction in each step of comparison. Porosity-permeability variation in a 2D pore structure and mass transfer coefficient in a closed-end fracture with porous walls are then evaluated under different flow conditions.

Introduction. In recent years, substances extracted from plant materials have been widely used in the pharmaceutical, cosmetic and food industries. Such substances are used as solutions, dry extracts for the manufacture of medicines, dietary supplements, cosmetic creams, food additives in various forms – tablets, capsules, solutions, granular powders. The extraction of valuable substances from plant materials is carried out using the extraction process, which is carried out by various methods and in apparatuses of various designs. Earlier, a comparative study of the extraction of dioscin from fenugreek by various methods was carried out: in devices with a stirrer, in an ultrasonic field, supercritical, fluid CO2 extraction, and in a vibro-cavitation homogenizer. It is shown that the most effective method is the extraction carried out in a vibrocavitation homogenizer.Aim.To analyze the kinetics of the extraction of dioscin from fenugreek seeds, to determine the optimal values of the required degree of grinding of the raw materials, working temperature, the concentration of ethyl alcohol in the solution and the rotational speed of the rotor of the vibrocavitation homogenizer. Determine the effective mass transfer coefficient responsible for the intensity of mass transfer inside the particles.Materials and methods. An experimental study of the extraction of valuable components from plant materials was carried out in a laboratory unit with a vibrocavitation homogenizer of periodic action. As raw materials were used seeds of hay fenugreek, ecotype of Morocco, acquired in the company Fitokasa, Casablanca (Morocco), which we used for research. Commodity analysis showed that raw materials comply with the requirements of the State Pharmacopoeia XIVth edition. As extractants, aqueous solutions of ethanol with an alcohol concentration of 40, 50, 60, 70, 80, and 90 %. The analysis of the kinetics of the process was based on the following ideas. Extraction begins with the surface of the particles of plant material. As the extracted component moves into the volume of the solution, the extractant penetrates into the internal pores of the particles, and the surface on which the extractant and the extracted component interact is gradually shifted into the individual particles. In this case, the resistance to mass transfer in the region between the specified surface and the outer surface of the particle increases over time.Results and discussion. An analysis of the results shows that the rotor speed significantly intensifies the process. In addition, the influence of the rotor speed is most pronounced at the initial stage of the process, when the surface layers of particles of plant material are extracted. It was also found that the resistance to mass transfer inside particles increases significantly as it approaches the final stage of the process, and with an increase in the rotor speed, it increases, especially at the initial stage of the process, which is associated with the intensity of cavitation and the weakening of its effect as the process deepens inward particles.Conclusions. The obtained dependences are necessary to determine the duration of the extraction process in a batch mode, or the average residence time of seeds in the working volume when organizing the process in a continuous mode.

To investigate the influence of fluid purity on the adsorption properties, adsorption kinetics and adsorption equilibria of two methanol samples with different water content on an activated carbon were studied. The purity of the methanol samples was 98.5% and 99.9%. Measurements were conducted at 298 K and 318 K using a magnetic suspension balance and cover a wide p/p0 range. To determine effective diffusion time constants and mass transfer coefficients, adsorption kinetics were evaluated using an isothermal and a nonisothermal Fickian diffusion model, and the linear driving force model. The pressure dependence of the kinetic parameters was studied and discussed. A small influence of sample purity on the adsorption equilibria was observed, as the purer methanol sample showed slightly higher equilibrium loadings than the less pure sample. However, significantly faster adsorption kinetics were observed for the purer sample at all temperature and pressure conditions. Compared to the less pure sample, the determined effective diffusion time constants and the mass transfer coefficients were up to 98% and 35% higher, respectively.

Propylene glycol, also known as 1,2 propanediol, is one of the most important chemicals in the industry. It is a water-soluble liquid, considered by the U.S. Food and Drug Administration as safe to manufacture consumer products, including foodstuffs, medicines, and cosmetics. This chemical has essential properties, such as solvent, moisturizer, or antifreeze, in addition to a low level of toxicity. This paper aims to present the selection, simulation, and dimensioning of a trickle bed reactor at a laboratory scale. The sizing was validated with other authors. Two predictive models have been considered for reactor modeling, intrinsic kinetics and coupled intrinsic kinetics, along with mass transfer equations and the wetting of the catalyst particles. The model was implemented using Aspen Custom Modeler® (20 Crosby Dr. Bedford, MA 01730, EE. UU.) to study the reactor behavior in terms of conversion. The results show the profiles of different variables throughout the reactor and present higher glycerol conversion when mass transfer is added to the model.

The mass transfer coefficients, interfacial area and pressure drop of a packed bed are essential properties that need to be evaluated prior to the design of a CO2 absorption column. Various mathematical models have been proposed to predict these properties under different process conditions. This work has compared several mathematical models for pressure drop, mass transfer coefficients and interfacial area and discussed how the uncertainty of physical properties and process conditions affect the evaluation of packed bed height in a CO2 absorption column. A case study has been performed to study the propagation of uncertainty in input variables through the packed bed height design equations. Here, it was found as 12% from uncertainty in physical properties and 60% from uncertainty in choice of mathematical model of the calculated packed bed height. A recommended safety factor for the absorption packing height is 60 % for a generic packing, but this safety factor can be reduced considerably if experimental data for pressure drop and mass transfer coefficients are available for the specific packing.

To investigate mass transfer of phosphorus in hot-metal dephosphorization process, it is necessary to reduce the deviation of traditional dephosphorization models in fitting accuracy. According to the change in hot-metal phosphorus content during dephosphorization, a new dephosphorization model was established by introducing the concept of “dynamic relative area”. With the help of literature data and comparative analysis of the new and old models, the rationality of the new model was verified. On this basis, in order to reveal the effects of CaO and its derivatives on mass transfer of phosphorus, based on the dephosphorization effect of FetO–CaO–SiO2–CaCl2 slags on high-phosphorus hot metal at 1673 K (1400 °C), the mass transfer process of phosphorus was investigated by calculating, analyzing, and discussing the overall mass transfer coefficients of phosphorus using CaO, Ca(OH)2, and CaCO3 with equal molar amount as fixatives (slag formers) in dephosphorizer respectively. The results show that the overall mass transfer coefficients of phosphorus under the action of Ca(OH)2 and CaCO3 are 0.0216 cm/s and 0.0363 cm/s, respectively, which are significantly lower than 0.0840 cm/s under the action of CaO.

This study assesses the mass transfer of compounds inside the US EPA flux hood, one of the enclosure devices most commonly employed for the direct measurement of atmospheric emissions from liquid surfaces in wastewater treatment plants (WWTPs). Experiments comprised the evaporation of water and the volatilisation of a range of volatile organic compounds (VOCs). Special attention was given to the evaluation of the mass transfer coefficients in the microenvironment created by the flux hood and the effects of concentration build up in the hood's headspace. The VOCs emission rates and the water evaporation rates generally increased with the sweep air flow rate, as did the mass transfer coefficients for all compounds. The emission of compounds whose volatilisation is significantly influenced by the gas phase was greatly affected by concentration build up, whereas this effect was not significant for liquid phase-controlled compounds. The gas-film mass transfer coefficient ( k G ) estimated inside the US EPA flux hood was of the same order as the respective k G reported in the literature for wind tunnel-type devices, but the emission rates measured by the flux hood can be expected to be lower, due to the concentration build-up. Compared against an emission model for the passive surfaces in WWTPs, the mass transfer of acetic acid (representing a gas phase-dominated compound) inside the US EPA flux hood was equivalent to conditions of wind speeds at 10 m height ( U 10 ) of 0.27, 0.51 and 0.99 m s−1, respectively, for sweep air flow rates of 2, 5 and 10 L min−1. On the other hand, for higher wind speeds, the emission rates of gas phase-controlled compounds obtained with the flux hood can be considerably underestimated: for instance, at U 10 = 5 m s−1, the emission rates of acetic acid inside the flux hood would be approximately 23, 12 and 6 times lower than the emission rates in the field, for sweep air flow rates of 2, 5 and 10 L min−1, respectively. A procedure is presented in order to scale the emission rates of these compounds measured with the flux hood to field conditions of higher winds.

Accurate knowledge of volumetric oxygen mass transfer coefficients in multiphase systems is important for successfully designing and efficient operation of process plants. As a result, a large number of papers on the determination of volumetric mass transfer coefficients k L a have been published in the literature. The dynamic degassing method is probably the most common method for determining the volumetric mass transfer coefficient. However, little work is known on the influence of countercurrent diffusion effects, arising from further dissolved components, on the volumetric mass transfer coefficient. For this reason, the effect of countercurrent diffusion is investigated in the present work by using different stripping gases to determine the volumetric oxygen mass transfer coefficient. Furthermore, the effect of counterdiffusion is investigated for both conventional aeration and aeration with microbubbles. The present work shows that the choice of stripping gas has a decisive influence on the determination of the volumetric oxygen mass transfer coefficient. Moreover, it can be shown that this effect is directly proportional to the solubility of the stripping gas in the aqueous phase. Simultaneous measurements of bubble size distributions allow determining mass transfer coefficients k L . A model is developed describing the decrease in the mass transfer coefficient as a function of the solubility of the stripping gas. Furthermore, it can be shown that for the experimental determination of volumetric oxygen mass transfer coefficients, the choice of stripping gas should be adapted to secondary gas types occurring within real processes achieving a better comparability.

A adsorção é uma técnica amplamente utilizada nos processos de tratamento de águas e efluentes industriais. Entender a cinética deste fenômeno é fundamental para obter informações sobre os mecanismos que ocorrem durante a transferência de massa e avaliar o desempenho de um determinado adsorvente. Vários modelos matemáticos foram desenvolvidos para descrever os processos que ocorrem na adsorção, entretanto, esses modelos são frequentemente empregados para ajustar os dados cinéticos de maneira errônea ou inadequada. Isso ocorre principalmente porque as condições de contorno e/ou iniciais dos modelos não são adequadas para o processo que está sendo avaliado. Com base nessas considerações, o presente trabalho tem como objetivo estimar os coeficientes cinéticos da transferência de massa da adsorção em sistemas sólido-líquido em batelada. Além disso, será realizada uma revisão crítica dos principais modelos utilizados na literatura para estimação e a análise da estimabilidade desses coeficientes. Experimentos de equilíbrio e cinética de adsorção foram realizados com os corantes Verde Rápido, Azul de Metileno e Vermelho Allura utilizando como adsorvente a alumina Pural SB e carvão ativado com duas faixas diferentes de diâmetro (Mesh 14-18 e Mesh 100-200), a revisão crítica foi feita com base em alguns dos modelos presentes na literatura para a estimação dos coeficientes de transferência de massa. A partir dos dados coletados nestes experimentos, estimou-se o coeficiente convectivo pelas metodologias propostas por Furusawa-Smith (1973), Yao-Chen (2015), Mathews-Weber (1976) e modelos fenomenológicos. A difusividade foi determinada utilizando-se os modelos apresentados por Boyd (1947) - Reichenberg (1953), Yao-Chen (2015), Vermeulen (1953) e o modelo fenomenológico. Os parâmetros das metodologias simplificadas foram estimados utilizando o software STATISTICA. Para o modelo fenomenológico a solução foi realizada numericamente por meio da discretização por diferenças finitas e posterior integração do sistema de EDO’s resultante com o auxílio da rotina DASSL. A estimação dos parâmetros de transferência de massa foi feita simultaneamente minimizando-se a função objetivo de mínimos quadrados ponderados pelo método do Enxame de Partículas (PSO) associado ao método de Newton. O coeficiente de transferência de massa convectivo calculado pelas metodologias simplificadas apresentou valores finitos na ordem de 10-2 e 10-3 cm/min, enquanto que utilizando-se o modelo fenomenológico o valor deste parâmetro tendeu ao infinito. A difusividade pelos modelos simplificados apresentou valores bastante próximos aos do modelo fenomenológico. Analisando-se os resultados, verificou-se que a estimação simultânea dos parâmetros de transferência de massa a partir de um modelo teórico baseado em balanços de massa é mais adequada e que os métodos que buscam simplificar a determinação desses coeficientes são extremamente limitados ou possuem hipóteses distantes da realidade. Adsorption is a technique widely used in water and industrial effluent treatment processes. Understanding the kinetics of this phenomenon is fundamental to obtain information about the mechanisms that occur during mass transfer and evaluate the performance of a specific adsorbent. Several mathematical models have been developed to describe the processes that occur in adsorption however, these models are often used to adjust the kinetic data in an erroneous or inappropriate form. This is mainly because the boundary and/or initial conditions of the models are not appropriate for the process being evaluated. Based on these considerations, this study intends to estimate the kinetic coefficients of adsorption mass transfer in solid-liquid batch systems. In addition, a critical review of the main models used in the literature for estimation and analysis of the estimability of these coefficients will be performed. Equilibrium and adsorption kinetics experiments were performed with the colorants Fast Green, Methylene Blue and Allura Red using Pural SB alumina and activated carbon with two different ranges of diameter (Mesh 14-18 and Mesh 100-200) as adsorbent, the critical review was made based on some of the models present in the literature for the estimation of mass transfer coefficients. From the data collected in these experiments, the convective coefficient was estimated using the methodologies proposed by Furusawa-Smith (1973), Yao-Chen (2015), Mathews-Weber (1976) and phenomenological models and the diffusivity using the models presented by Boyd (1947)-Reichenberg (1953), Yao-Chen (2015), Vermeulen (1953) and the phenomenological model. The parameters of the simplified methodologies were estimated using the STATISTICA software. For the phenomenological model the solution was numerically carried out through the discretization by finite differences and subsequent integration of the resulting EDO system with the aid of the DASSL routine. The estimation of the mass transfer parameters was made simultaneously minimizing the objective function of least squares weighted by the method of Particle Swarm Optimization (PSO) associated with the Newton's method. The convective mass transfer coefficient calculated by the simplified methodologies presented finite values in the order of 10-2 and 10-3 cm/min, while using the phenomenological model the value of this parameter tended to infinity. The diffusivity of the simplified models presented values quite close to those of the phenomenological model. Analyzing the results, it was found that the simultaneous estimation of the mass transfer parameters from a theoretical model based on mass balances is more appropriate and that methods that seek to simplify the determination of these coefficients are extremely limited or have hypotheses distant from reality.

Mass and heat transfer coefficients (MTC and HTC) in automotive exhaust catalytic monolith channels are estimated and correlated for a wide range of gas velocities and prevailing conditions of small up to real size converters. The coefficient estimation is based on a two dimensional computational fluid dynamic (2-D CFD) model developed in Comsol Multiphysics, taking into account catalytic rates of a real catalytic converter. The effect of channel size and reaction rates on mass and heat transfer coefficients and the applicability of the proposed correlations at different conditions are discussed. The correlations proposed predict very satisfactorily the mass and heat transfer coefficients calculated from the 2-D CFD model along the channel length. The use of a one dimensional (1-D) simplified model that couples a plug flow reactor (PFR) with mass transport and heat transport effects using the mass and heat transfer correlations of this study is proved to be appropriate for the simulation of the monolith channel operation.

Plant leaves play an important role in the fate of hydrophobic organic contaminants (HOCs) in the environment. Yet much remains unknown about the permeability of leaves by HOCs. In this pilot study we measured (i) the kinetics of mass transfer of three polycyclic aromatic hydrocarbons (PAHs) and six polychlorinated biphenyls between a spiked and an unspiked sheet of polydimethylsiloxane (PDMS) in direct contact with each other for 24 h and (ii) kinetics of mass transfer of two PAHs through leaves and low-density polyethylene (LDPE) in a passive dosing experiment by inserting these matrices between the two sheets of PDMS for 48 h. The kinetics of mass transfer of fluoranthene between PDMS sheets in direct contact were a factor of 12 slower than those reported in the literature. The kinetics of mass transfer of fluorene and phenanthrene through leaves were within the range of those previously reported for 2,4-dichlorophenoxyacetic acid through isolated cuticles. Our results provide a proof-of-concept demonstration that the passive dosing method applied in this study can be used to measure the mass transfer coefficients of organic chemicals through leaves. Key recommendations for future experiments are to load the PDMS at the highest feasible concentrations to avoid working at analyte levels close to the limit of detection, to keep the leaves moist and to minimize potential pathways for contamination of the PDMS sheets by exposure to laboratory air.

Ultrasound was applied to enhance mass transfer within the boundary layer during wood vacuum drying. Fast growing poplar (Populus tomentosa) was used as the specimen in this work. The water migration rates and the mass transfer coefficients were studied at temperatures of 35 and 50 °C, absolute pressures of 0.03, 0.06, and 0.1 MPa, and ultrasound power-frequency groups of 60 W-28 kHz, 100 W-28 kHz, and 100 W-20 kHz, respectively. The results indicated that ultrasound could markedly increase the water migration rates within the boundary layer. The water migration rates increased with increasing ultrasound power and frequency. The mass transfer coefficients within the boundary layer for specimens treated with ultrasound were much higher than those of the control group, and the mass transfer coefficients increased with decreasing absolute pressure. Ultrasound could be applied in the wood drying industry as a means of saving time and energy.

A complex study of the operation of supported ionic liquid membranes from practical point of view was made. It was shown that supported ionic liquids are selective for the binary mixture of CH4/CO2. Unfortunately, the literature reports certain pure ionic liquid data, which are mainly focused on CO2 and there is lack of data for CH4. The main problem seems to be the lack of data of the diffusion coefficients of gases in ionic liquids and, consequently, there are no correlations avialable between the transport properties and the molecular properties of the gas and of the IL.. The data available in literature are measured and calculated for pure ionic liquids only but there is no reasonable way how to apply them to the supported ionic liquid membranes. All the literature data sets overestimate at least twice the membrane performance in terms of pemeability and selectivity. Such a discrepancy brings the supported ionic liquid membranes into an inconvenient position from the point of view of practical application because it is not possible to design a process reliably although the supported ionic liquid membranes are comparable in separation characteristics to the best polymeric membrane (see Robeson plot Fig. 7). The reasons why the theoretical models overpredict the real values of permeation fluxes may be summarized below: o The mass transfer resistance of the support is not negligible, as often assumed o Some pores of the support are not opened for permeation o The structure of the support obstructs the maximal saturation of the liquid with the gas or in other words the initial concentration of the gas in the liquid does not reach the expected equilibrium value. None of these reasons should be totally excluded. A simple model of transport of gases through the liquid membrane in permeation cell was suggested. It showed that in the used pressure range (150-350kPa), the mass transfer coefficient may be assumed constant with reasonable accuracy. The model could be applied in the scale-up of the process because it takes into account the decrease of the driving force that occurs along the membrane. This decrease is not really significant in the lab scale process, where the membrane area is small, but it may be important in larger scale processes, especially when the high enrichment of retentate is required. Generally, it can be concluded that the ionic liquid membranes are convenient for gas separation processes, but it is necessary to rely on the data connected to the supported liquid membranes themselves rather than on the data of pure (free) ionic liquids.

To obtain mass transfer coefficients of three baby food mixtures on cereal basis in a tunnel dryer, Bi-G drying correlation can be used. Experimental moisture content values for three mixtures at three different air temperatures (60, 80 and 100°C) and air velocities (0.5, 1.0 and 1.5 m/s) during tunnel drying were collected. Effective moisture diffusivities coefficients were calculated in two ways and for mixtures 1, 2 and 3 and ranged between 1.51 × 10-8 to 52.7 × 10-8 m2/s, 1.05 × 10-8 to 64.9 × 10-8 m2/s and 0.107 × 10-8 to 53.1 × 10-8 m2/s, respectively. At lower drying temperature, moisture diffusivities values calculated in two ways agreed better than at higher temperature. The influence of baby food composition on mass transfer parameters was observed. Key words: Baby food, exponential drying model, mass transfer coefficients, tunnel drying.

Department of Polymer Science and Technology, University of Calcutta, Kolkata-700 009, India E-mail : mausumial@gmail.com, bidyutbarank@yahoo.com, barnaliduttaroy84@gmail.com Manuscript received 21 January 2015, revised 02 March 2015, accepted 02 March 2015 Solvent absorptions were studied in vulcanized rubber samples of widely varying amounts of nano calcium carbonate with a view to rate-limiting steps, the major diffusion rate control and other solvent properties. The surface resistance (the mass flux through the polymer surface, Fs ) was found to affect the absorption process of the composites. The sorption results were interpreted by using first-order kinetic model. The S-shaped curvature clearly indicates that solvent uptake process is significantly control by surface resistance in the present experiment. The hap (the surface mass transfer coefficient) values for all the nano composite samples are always higher than the corresponding gum values. This indicates that time required for solvent molecules to get place on the composite sample surface is prominent. The B (the ratio of diffusional resistance and surface resistance) values ranging from 9 to 55, are not very high (i.e. Dc (diffusion coefficient corrected for free film exposed on two sides) value increases with filler loading. The comparable ED (the activation energy of diffusion) values of gum and composites, expect good elastic properties in composites. The values of n (an idea about the mechanism of solvent transport) obtained for the different nano composites show anomalous (0.5 < n < 1.0) behaviour.

Sulfate dry deposition increases the deteriorating effects on environment. Sulfate can be deposited from atmosphere to water via both particulate (SO4 2 :sulfate)and a gas(SO 2:sulfurdioxide)form.In this research, the fluxes of gaseous(SO 2)and particulate(SO 4 2)species were measured employing a water surface sampler(WSS)and glass fiber filters(GFFs)ontheknife−edge surrogate surface(KSSs)in the campus of Uludag University and the city of Bursa, Turkey.Sampling program was conducte dinter mittently between September2004and March2005.Average to talsulfate fluxes measured with the WS Satthe Uludag University campus and in the city of Bursa were58 ± 41and235 ± 43 mgm −2 d −1, respectively.The to talsulfate fluxe smeasure dat Bursa were highe rand this was probably due to greater sulfur containing species in it satmosphere.The dry deposition of gas eous SO 2 flux was calculated by sub tracting the particulate flux collected with the KSS s from the total flux(particulate sulfate plus SO 2 flux)obtained by the WSS.Anautomatic SO 2 analyzer was used concurrently to measure the ambient concentration of gas eous SO 2. The average SO2 gas fluxes and ambient SO 2 concentrations were18 ± 28and54 ± 48 mgm ⊟2 day ⊟1 and11 ± 7and49 ± 14 μgm ⊟3 for the campus and the city, respectively.The measured gaseous SO 2 fluxes and ambient concentrations were used to calculate the mass transfer coefficient.The calculated MTC values for the campus and the city were0.8 ± 1.0and1.2 ± 1.1 cms ⊟1, respectively.The sevalues wereinag reement with previously reported dry deposition velocities for SO 2.

Two-phase and slurry bubble columns are characterized with high volumetric mass transfer coefficients kLa at low energy input. The design, modelling, optimization and scale-up of these reactors require precise knowledge of the mass transfer parameters. The mass transfer coefficients determine the efficiency and dimensions of (slurry) bubble columns. Nedeltchev et al. (2007) developed a correlation for prediction of mass transfer coefficients in gas-liquid bubble columns operated in the homogeneous flow regime. It was based on experimental gas holdups. On the other hand, Nedeltchev and Schumpe (2008) developed a correlation for prediction of gas holdups in gas-liquid bubble columns operated in the homogeneous regime. In this work, the theoretically calculated gas holdups were substituted in the mass transfer model (in the correlation for the interfacial area) of Nedeltchev et al. (2007) and the mass transfer coefficients were recalculated by means of a purely theoretical approach. The same gases and liquids (18 pure organic liquids, 14 adjusted liquid mixtures and tap water) were used and 263 kLa values (only in the homogeneous regime) were successfully predicted at ambient and high pressures (up to 1 MPa). The same approach was tested in a slurry bubble column. Nedeltchev et al. (2014) predicted successfully the experimental mass transfer coefficients in a slurry bubble column based on bubble sizes which depended on the experimental gas holdups. On the other hand, Nedeltchev (2014) established a new approach for predicting the gas holdups in a slurry bubble column. When these theoretical gas holdups were substituted in the mass transfer model (in the correlations for prediction of bubble size and interfacial area), a purely theoretical kLa values in a slurry bubble column were obtained. The predictions were good not only in the homogeneous regime but also in the heterogeneous regime. The theoretical approach was applicable up to relatively high (18 %) solids concentrations. Six different liquid-solid systems were used and 66 kLa values were successfully predicted. In both mass transfer models, correction factors (a function of Eӧtvӧs numbers) were introduced due to the non-spherical (ellipsoidal) shape of the bubbles.

A counter-current multistage extraction column having high performance (i.e., highextraction efficiency and large maximum throughput) has been developed. The hydrodynamic behavior and the mass transfercharacteristics of the column were ana-lyzed experimentally. Each stage of the column consists of lower mixer part, upper settler partand a drop coalescer between them. Both of the continuous and the dis-persed phases rise from the mixer into the settler and areseperated into two phases within the settler. The continuous phase goes down to the lower stage mixer through the downspout pipes and the dispersed phase rises to the upper stage mixer through the riser pipes. The maximum throughput in the column is independent of the drop size because the counter-current flow in the dispersion situation is avoided. Then the column can be operated at a strongagitation where the extraction efficiency is high due to large interfacial area with small drops. As the hydrodynamic behavior, the maximum throughput, the holdup of dispersed phase and the drop size were ex-amined. The maximum throughput can be determined from the balance between the pressure drop within the downspout and the sum of the suction pressure induced by the impeller and the buoyant force of dispersed phase. The holdup of the dis-persed phase in the mixer is given by a model of dispersed phase leaving the mixer, including the diffusional flow of dispersed phase. The drop size in the mixer de-pends on the residence time of the dispersed phase as well as the Weber number. The mass transfer characteristics can be expressed by a rigid sphere model of drop because the drop diameter is small at a strong agitation in the mixer. A theoretical model of diffusion within a rigid sphere gives the mass transfer coefficient in the dispersed phase, and the correlation by Ranz-Marshall for the mass transfer around a rigid sphere gives the mass transfer coefficient in the continuous phase. The ex-traction of copper with the five-stage mixer settler extraction column was represented by the calculation with the above hydrodynamic and mass transfer characteristics as well as the extraction reaction rate at the interface.

La corrosión por CO2/H2S en la producción de gas y petróleo es una de las áreas de investigación más importantes, debido a la necesidad de evaluar la severidad de la corrosión, disminuir el riesgo de problemas en operación y además bajar los costos de producción. En Colombia, las investigaciones se orientan hacia la corrosión por CO2, a pesar de la existencia de trazas de H2S, que son un peligro potencial para los materiales de las líneas de transporte de hidrocarburos. En este artículo se analiza la experimentación y los resultados del acero expuesto a un sistema Salmuera/CO2/H2S en un cilindro rotatorio. En esta geometría se determinaron las velocidades de corrosión sobre el acero AISI 1020, así como los coeficientes de transferencia de masa y capas viscosas de las especies más representativas del sistema. Adicionalmente, se caracterizó la morfología de los productos de corrosión formados en estos ambientes. El estudio permitió concluir que las especies relacionadas con el CO2 (H2CO3) son las que influyen sobre el mecanismo de deterioro del acero AISI 1020, que está fuertemente influenciado por la variación de la velocidad, la temperatura y el pH. The corrosion by CO2/ H2S in gas and petroleum production represents one of the most important areas of research, due to the necessity to evaluating the severity of corrosion and thus to decrease the risk of operation problems and in addition the decrease of effective costs of production. In Colombia, the researchers have been oriented to the study of CO2 corrosion, although in the country production can appear traces of H2S, which are potentially harmful for the materials of the hydrocarbon transporting pipelines. In this first part, the steel in a multiphase system containing brine-CO2-H2S was evaluated. To carry out this research, the concentrations of CO2 and H2S and the hydrodynamics conditions present in the pipelines were simulated in an electrode rotating cylinder. In this geometry, the corrosion rate was determined on steel AISI 1020, as well as, the mass transfer coefficients and viscous layers of the representative species of the system; the morphology of corrosion products formed in these environments was also characterized. This study allowed concluding that the species related to CO2 (H2CO3), are those that influence the mechanism of deterioration of steel AISI 1020. This behavior was strongly influenced by the variation of the electrode speed, the temperature and pH.

Se estudió la deshidratación osmótica de la castaña en disoluciones acuosas de sal (17, 22, 26,5 % p/p), sacarosa (40, 50, 60 % p/p) y glucosa (40, 50, 56,5 % p/p) a diferentes grados de agitación (0, 40, 110 rpm) y tiempos (1, 2, 4, 8 h) a 20 ºC. En las disoluciones de glucosa se estudió el efecto de la temperatura (50 ºC). Se determinaron los parámetros cinéticos de ganancia de sólidos, pérdida de agua, reducción de peso y relación pérdida de agua-ganancia de sólidos. Al aumentar la agitación, aumentó la ganancia de sólidos, la pérdida de agua y disminuyó la relación entre ambos, especialmente cuando las disoluciones tuvieron elevada viscosidad. Las cinéticas de los contenidos de humedad y de sólidos se modelizaron mediante la ecuación de Hawkes y Flink para tiempos cortos. Se determinaron los coeficientes de transferencia para el agua y el soluto osmótico y los coeficientes de difusividad mediante la ley de Fick. Chestnut fruits were submitted to osmotic dehydration in sodium chloride (17, 22, 26.5 % w/w), sucrose (40, 50, 60 % w/w) and glucose (40, 50, 56.5 % w/w) solutions at different stirring rates (0, 40, 110 rpm) and periods of time (1, 2, 4, 8 h) at 20 ºC. The effect of temperature (50 ºC) was studied in the case of samples dehydrated with glucose solutions. Several parameters for each dehydration process such as solids gain, water loss, and its corresponding ratio and weight reduction, were determined. High stirring rates increased solids gain and decreased water loss and its ratio, especially in the case of solutions of high viscosity. Moisture and solids gain contents were modelled by Hawkes and Flink equation for short times and water and osmotic solute transfer coefficients were calculated. The corresponding effective coefficients of diffusion were also evaluated by means of Fick’s law. Los autores agradecen a la Xunta de Galicia (España) y a FEDER el apoyo parcial con el proyecto PGIDIT04TAL265004PR SI

The design of a liquid-liquid extraction column is based on energy transfer phenomenon leading to a fragmentation of the light phase in droplets allowing the mass transfer with the heavy phase. However, this mechanism suggests a recurring coalescence of the drops followed by a fragmentation to each plate. The process studied in this Thesis is based on the use of a pulsated column attached by optical techniques (analyzes images and Anemometry Doppler Laser) in order to investigate the processes of transfer and the hydrodynamic of the column. The selected experimental model consists of the study of the mass transfer from the dispersed phase (ethyl acetate) to the continuous phase (water) under the standard conditions. A better understanding of pulsed liquid-liquid extraction columns was obtained by using an online digital image analysis system to characterize emulsion drop. The system enabled drop size distribution (DSD) in the emulsion to be qualified with physical (flow rate, stirring pulse) and thermodynamic (surface tension) parameters. The surface tension was investigated by static contact angle measurement as a function of the mixture composition. Mass transfer and energy transfer, characterized by the surface/volume ratio of the droplets were compared with the working parameters such as surface tension of the liquid in order to interpret restrictive phenomena such as hold up, flooding; transfer mass velocity and column efficiency. However, the adhesion work between liquid and plate surface determined by contact angle measurements indicates that interface property variations, as a function of solute concentration, must be taken into account in the theoretical correlations. A simulation code was used in order to estimate each plate's efficiency and to determine the limit of the energy transfer which is responsible for the flooding phenomena. The droplet rates and their residence time between each plate were estimated by ADL measurements and we simulate under Comsol 3.4 current lines and the phenomena turbulence for a pulsed system., La conception d'une colonne d'extraction liquide-liquide repose sur le mécanisme de transfert d'énergie conduisant à une fragmentation de la phase légère en gouttelettes permettant le transfert de matière avec la phase lourde. Toutefois ce mécanisme présente de façon récurrente à chaque plateau une coalescence des gouttes suivie d'une fragmentation. Le processus étudié dans ce mémoire repose sur l'emploi d'une colonne pulsée instrumentée par des techniques optiques (analyse d'images et Anémométrie Doppler Laser) afin de disposer d'outils non intrusifs pour qualifier les processus de transfert et l'hydrodynamique de la colonne. Le modèle expérimental choisi consiste à étudier le transfert de matière de l'acide acétique de la phase dispersée (acétate d'éthyle - acide acétique) à la phase continue (eau). Le système d'analyse d'image a permis de mesurer in situ la distribution des gouttes de la phase légère selon leur taille (DSD) en fonction des paramètres physicochimiques et thermodynamiques. La tension de surface de chaque liquide vis-à-vis des plateaux perforés (PTFE) a été déterminée à partir des mesures d'angle de contact. Les transferts d'énergie et de matière caractérisés par le rapport surface/volume des gouttes sont corrélés avec les paramètres d'action afin d'interpréter le phénomène restrictif tels que le Hold-up et l'efficacité de séparation. Cependant, l'étude du travail d'adhésion entre la goutte et la surface des plateaux indique que les variations des propriétés interfaciales sont fonction de la concentration du soluté et doit être prises en compte dans la corrélation du diamètre moyen de Sauter. Nous avons utilisé des codes industriels Hysys/Aspen afin d'établir le rôle déterminant de la tension de surface sur les codes de calcul et la convergence des modèles. A partir de ces modèles nous avons déterminer l'efficacité de chaque plateau et de mettre en évidence le rôle du transfert d'énergie responsable du phénomène d'engorgement. Nous avons estimé la vitesse moyenne et le temps de séjour moyen sur chaque plateau par ADL en fonction de l'énergie transmise au plateau par pulsation mécanique et à partir de ces résultats nous avons simulé sous Comsol 3.4 l'écoulement hydrodynamique de la colonne type pulsée.

The terminal velocity and mass transfer coefficients of drop swarms of high viscosity solvents were investigated to study the effect of viscosity on drop behavior in a column packed with super mini ring (SMR) packing. The experimental column was equipped with a multi-channel precise syringe pump and a computerized video imaging system. Cyanex 923S kerosene solutions of different concentrations were used as experimental systems, and their viscosities are ranged from 1.2 to 53.7 mPa S. The effect of drop size and viscosity on the mass transfer coefficient, Kod, has been studied. It is clear from the results that Kod decreases sharply with the increase of viscosity, whereas drop size only has a little effect on Kod. The SMR packing increases Kod significantly up to 100%. Calculations with well-known literature equations cannot predict our experimental data, thus a model considering the interfacial mobility was provided to predict Kod of high viscosity solvents. The model has an adjustable parameter easily obtained from experimental data and fits the experimental data well. A modified Klee–Treybal equation describing terminal velocity under mass transfer conditions was also proposed in this paper.

Average mass transfer coefficients within denitrifying biofilms were determined during biofilm growth with an inert compound (LiCl) in a membrane flow cell at different flow conditions, until the biofilm reached (pseudo-) steady state. Similar values were obtained for the steady-state mass transfer coefficients of LiCl within the different biofilms. However, those coefficients were higher during the transient period of biofilm growth for the biofilm developed under the highest upflow velocity., Xunta de Galicia, project BioToBio

Neural networks have been investigated for predicting mass transfer coefficients from supercritical Carbon Dioxide/Ethanol/Water system. To avoid the difficulties associated with reduce experimental data set available for supercritical extraction in question, it was chosen to use a technique to generate new semi-empirical data. It combines experimental mass transfer coefficient with those obtained from correlation available in literature, producing an extended data set enough for efficient neural network identification. With respect to available experimental data, the results obtained to benefit neural networks in comparing with empirical correlations for predicting mass transfer parameters.

Mass transfer coefficients within denitrifying biofilms were determined with an inert compound (LiCl) using two different flow conditions in a membrane flow cell and feeding an easily degradable substrate. The experiments were made until the biofilm reached steady state. The results obtained from the biofilm mass transfer experiments show that the biofilms grown under these two different conditions reach similar values in the steady state. However, the mass transport was higher during biofilm formation, for the biofilm developed under higher upflow velocity., Comissão Europeia, TMR program (project BioToBio); Spanish CICYT (project AMB 98-0288).

Average mass transfer coefficients of an inert compound (LiCl) within denitrifying biofilms were monitored during biofilm growth in a membrane flow cell under different flow conditions, until the biofilm reached (pseudo-) steady state. Average effective diffusivities were found to increase with the decrease in tortuosity factors of the biofilm matrix. The lowest tortuosity factor corresponded to the biofilm formed under the highest liquid velocity., União Europeia - BioToBio - ERBFMRXCT97-0114. Centro de Investigación Científica y Tecnológica (CICYT) - AMB 98-0288, PR404E 2000/6-0