Simple Mass Transfer Model Research Articles

Efficiency, Kinetics and Mechanism of 4-Nitroaniline Removal from Aqueous Solutions by Emulsion Liquid Membranes Using Type 1 Facilitated Transport.

4-Nitroaniline (4NA) is a common organic pollutant that is released into the environment during the manufacture and processing of a wide variety of industrial products. This article describes the use of an emulsion liquid membrane process to remove 4NA from aqueous solutions using a type 1 facilitated transport mechanism. Optimization of the removal process was carried out by analyzing the efficiency of 4NA removal from the feed phase and the initial apparent feed/membrane fluxes and permeabilities under different experimental conditions. The kinetics of the removal process was analyzed using a simplified mass transfer model involving an empirical mass transfer coefficient calculated from experimental data, assuming that the concentrations of 4NA in the external aqueous phase and in the internal w/o emulsion are uniform. The results show that there is a very good fit between the experimental and model data and that the variation in the values of the overall mass transfer coefficients with the experimental conditions coincides with that of the removal efficiency mentioned above. The transport mechanism was studied by identifying the rate-controlling step of the removal process, using models described for adsorption processes, due to the strong parallelism between the transport mechanisms in adsorption and emulsion liquid membrane processes.

Removal of soluble divalent manganese by superfine powdered activated carbon and free chlorine: Development and application of a simple kinetic model of mass transfer–catalytic surface oxidation

Catalytic oxidative removal of Mn2+ on activated-carbon surfaces by free chlorine was recently discovered and found to be potentially practicable for water treatment when using micrometer-sized activated carbon. Herein, we newly derived a kinetic model for trace-substance removal by catalytic reaction and applied it to the Mn2+ removal. External-film mass transfer, adsorption, and oxidation/desorption contributed similarly to the Mn2+ removal rate under actual practical conditions. The low removal rate in natural water was attributed to decreases in available adsorption sites: e.g., a 50% decrease in available sites in water with 0.26 mmol-Ca2+/L caused a 15% reduction in removal rate. Low temperature greatly reduced the removal rate by both enhancing the decrease in available sites and hindering mass transfer through increased viscosity. While adsorption sites differed 8-fold between different carbon particles, causing a 2.2-fold difference in removal rates, carbon particle size was more influential, with a >10-fold difference between 2- and 30-μm sizes.

Supercritical CO2 extraction of pinocembrin from Lippia origanoides distillation residues. 1. Multicomponent solubility and equilibrium partition

Steam-distilled oregano (Lippia origanoides) distillation process was analyzed and described as a model binary mixture. The most abundant identified and selected compounds were pinocembrin, a high-value flavonoid, as representative of the minor fraction, and octacosane, a cuticular wax, of the major fraction. Thermodynamic solubility of the solid multicomponent mixture in supercritical CO2 was measured at 313 K and 323 K, and pressures from 8.6 to 32.1 MPa, using a dynamic-analytical method with on-line HPLC analysis. The molar fraction of pinocembrin in CO2-rich phase was assessed from 4.8·10−6 to 33·10−6 mol/mol. The solid + fluid equilibrium for the ternary model system was modeled with the Peng-Robinson equation of state and the classical van der Waals mixing rules. Extraction experiments of the solid multicomponent mixture with supercritical CO2 modified with 2–9% w/w ethanol, were carried out in a one-pass pilot scale apparatus at 308 K, 323 K and 338 K, and pressures of 18 MPa, 26 MPa, and 34 MPa. For each sample, the pinocembrin content was assessed. The extraction curves for oleoresin and pinocembrin were represented with empirical models from which the oleoresin partition constants were estimated, that were in range from 0.03 to 0.13 kg/kg substrate/CO2 depending on extraction conditions. However, the partition constant remained virtually invariant, independently of changes in the extraction temperature and pressure conditions, and the ethanol content in CO2, with an average value of 0.08 kg/kg substrate/CO2. These results will facilitate using a simplified mass transfer model to describe oleoresin extraction from steam-distilled L. origanoides.

Derivation and validation of a simplified analytical mass transfer model of the laminar co-flow tube for nucleation studies

A laminar co-flow tube is a device recently developed by the present team to study the formation of aerosol particles in atmospherically relevant vapor mixtures. The device employs isothermal mutual diffusion of vapors in two merging laminar gas flows, each saturated with a different vapor. The main quantity of interest, namely, the nucleation rate at which aerosol particles are formed at given temperatures and vapor concentrations, is not measured directly. Therefore, a mass transfer model is needed to evaluate the local nucleation rate and local concentrations obtained from measured integral quantities the flow rates and vapor concentrations at the inlets and the number concentration of generated aerosol particles at the tube outlet. This article presents the derivation and testing of an analytical simplified mass transfer model in which the diffusion problem is solved with approximations for simplification. The purpose of the simplified model is to provide a tool suitable for experimental design and evaluation of results that does not require lengthy computations and transparently shows the effects of the main parameters. By idealizing the velocity field in the co-flow section as plug flow and neglecting axial dispersion, the governing equations of mass transport reduce to a 1D unsteady diffusion problem in cylindrical coordinates moving with the fluid. Such a simplified model has an analytical solution in the form of an infinite series. The simplified mass transfer model is tested for particle formation in the sulfuric acid-water system. New experimental data for particle formation at temperatures of 15 ∘C and 27 ∘C at a relative humidity of 0.38 and various sulfuric acid concentrations are provided as a basis for testing. The results of the model are compared with numerical Computational Fluid Dynamics (CFD) simulations of the full mass and momentum transfer problem. The appropriate choice of plug-flow velocity for the analytical model is discussed. In this connection, hydrodynamics in the undeveloped region of the co-flow are described in detail. Based on the hydrodynamic entrance length, two essential fluid flow regimes are identified. The model results and CFD simulations show a nucleation zone with a shape resembling a candle flame located in the central part of the laminar co-flow tube, with a maximum nucleation rate at the tube axis. The main quantitative characteristics of the particle formation evaluated with the help of the simplified model and with CFD simulations are compared. It turns out that, especially when choosing the plug-flow velocity appropriately, the difference between the numerical CFD model and the simplified analytical model is less than the experimental uncertainty of the measured data. This justifies the application of the simplified mass transfer model for the purpose of quantitative evaluation of experiments with the laminar co-flow tube. This article presents new details of the mass transfer processes and evaluation procedures for the novel experimental device exemplified with a new set of experimental data for particle formation in a sulfuric acid-water system.

Influence of heat transfer on the estimation of water vapor diffusion coefficient in transient regime

The use of bio-sourced materials for thermal insulation of buildings is growing mainly for environmental reasons. It has already been demonstrated that since these materials are highly hydrophilic, mass transfer may have significant influence on their temperature field. We first develop a heat and mass transfer model with a limited number of parameters and we use it to simulate the mass and temperature fields during a typical transient experiment dedicated to vapor diffusion coefficient estimation. Estimations made from these simulations with a simple mass transfer model show that the estimation error can be greater than 30 % in some cases. A sensitivity study shows that the vapor diffusion coefficient, the thermal conductivity and the external mass transfer coefficient can be estimated separately from a mass recording, with the coupled model. An experimental study carried out at 15°C, 25°C and 35°C on a wood fiber board confirms the results of the theoretical study. The deviation between the vapor diffusion coefficient estimated with and without taking into account the heat transfer was 13.3 % at 35°C. It is finally shown that the isosteric heat of sorption has no effect on the estimation of the diffusion coefficient.

Euler–Euler model for CO2-MEA reactive absorption on a sieve-tray

CFD studies dedicated to Carbon Capture and Storage are still limited to simple geometries or mass transfer models. In this work, the CO2-MEA system is studied through a three-dimensional, transient, Eulerian–Eulerian model. A sieve-tray is chosen as case study and a global mass transfer coefficient model is implemented. A preliminary validation study in an air-water system is made to assess which drag force correlation provides better results for local clear liquid height, and therefore experimental measures for local clear liquid heights are also taken. Relative errors of about 20% are obtained for total clear-liquid height measures, and the numerical results are qualitatively validated. For the reactive absorption cases, CO2 is fully absorbed and consumed in the liquid phase, while with disabled chemical reaction less than 90% is absorbed. The implemented model physical consistency reinforces the potential of using CFD techniques for process intensification scale-up and design.

Determination of diffusion coefficient of a miscible CO2/n-hexadecane system with Dynamic Pendant Drop Volume Analysis (DPDVA) technique

A clear understanding of the diffusion characteristics between oil and CO2 phase in the miscible front is substantial to operate a successful CO2 miscible flooding process. However, there are few studies on diffusion characteristics of CO2/hydrocarbon systems under the multi-contact miscible state. In this paper, the Dynamic Pendant Drop Volume Analysis (DPDVA) technique is employed to obtain the diffusion coefficients of the CO2/n-hexadecane system over the Minimum Miscibility Pressure (MMP) conditions. Based on the oil droplet volume variation histories, a simplified mass transfer model adapted to the oil-gas miscibility condition is proposed. For the first time, the diffusion coefficients of a miscible CO2/n-hexadecane system at temperature range of 26.9–79.6 °C and the pressure range of 7–19 MPa were measured. It is found the diffusion coefficients close to the MMP condition have the same magnitude values compared to the literature reported results in immiscible conditions, indicating a nearly stable diffusion rate before system miscibility and in the meantime validating the experimental technique employed in this paper. On the other hand, larger diffusion coefficient appears under lower temperature and higher pressure conditions under miscible conditions, and a clearly linear relationship is observed between the diffusion coefficient and the system pressure. It is expected the study can fill some gaps in the research field of oil/gas miscible diffusion characteristics and help optimize the gas injection miscible flooding processes.

Experimental and Analytical Characterization of Firebrand Ignition of Home Insulation Materials

Wildland firebrands are known to ignite materials in attic spaces of homes. To clarify the effects of choices in attic insulation materials for homes located at the wildland urban interface, this study seeks to characterize the effects of firebrand characteristics on the ignition propensity of several common insulation materials: polyurethane foam, expanded polystyrene (EPS), extruded polystyrene (XPS), flame retarded and non-flame retarded denim, and flame retarded and non-flame retarded loosefill cellulose. An experimental system was developed to explore the effects of firebrand heating, air flow, and firebrand configuration on ignition. For an equal initial mass of wooden material, two firebrand configurations were generated: a single whole firebrand and multiple (five) fragmented firebrands. Relative to whole firebrands, the fragmented firebrands were found to more reliably ignite the insulation materials. Thermoplastic insulation material would only ignite in a temporary flash flame, but did not support sustained burning. Following the flash flame, the firebrands would melt through the synthetic polymer material (XPS and EPS) and cease smoldering. Cellulosic insulation materials would ignite in a sustained fire provided that there was adequate air flow. A simple heat and mass transfer model was developed to describe the ignition process due to firebrand deposition. Traditional lab-scale experiments, thermogravimetric analysis and cone calorimetry, were performed to parameterize the model. Results followed experimentally observed firebrand temperature patterns. There was an average error of approximately 8.5% between firebrand temperature model predictions and experimental measurements. Also, consistent with the experimental results, the model predicted that increasing air flow increased ember temperature and reduced the time to ignition for cases in which ignition occurs.

Feasibility of Using Wood Chips to Regulate Relative Humidity Inside a Building: A Numerical Study

The use of bio-based materials in buildings has become more and more significant last years. In most of the cases, their health properties and natural provenance have made them a great solution to face global climate warming and the new policies to reduce building energy consumption. In many thermal problems, bio-based materials can allow to optimize the building thermal behavior according to its energy consumption and inside comfort conditions. So it is when they are used as an insulation material in the building. However, it is not the case in this paper. In fact, the bio-based matter is rather used as a desiccant wheel to control air conditioning inside the building. The aim of this paper is to numerically verify if it is possible to use a bed of wood chips as a hygroscopic material (or a desiccant matter) in order to modify the relative humidity inside the building in Reunion Island and so improve thermal comfort. A simple model of heat and mass transfer between a bed of wood chips and building inside air has been set up and implemented into a validated building simulation code named ISOLAB. Numerical simulations were set up for the four climate zones of the island regulations and a focus has been made on the low altitude one (with high, solar irradiation, temperature and relative humidity). Simulation results give the thermal behavior of the building particularly the temperature and relative humidity of inside air temperature, and temperature and moisture content of wood chips. The obtained results lead to determine if the wood chips bed is suitable for the reference building and to verify its technical feasibility (wood species, size of the bed, integration to the building, etc.). The results show that the use of a WCB help to decrease the building inside air temperature and water content up to 10°C less and 11.6 g.kg-1 less. These are the ways to improve inside comfort conditions. Indeed, comfort analysis have shown the possibility to significantly increase building users’ thermal comfort when coupled with a fan and natural ventilation, like the regulation needs for low altitude climate. In this case, a gain of 68% of year time is achieved for a building equipped with WCB system compared to one without it (6308 hours of comfort over a year with the WCB against 350 hours without WCB). So the WCB seems to be able to help reducing cooling loads in tropical climate conditions.

Membrane contactor reactor for transesterification of triglycerides heterogeneously catalyzed

A membrane reactor was developed for coupling heterogeneously catalyzed transesterification and glycerol extraction using a membrane contactor. The membrane contactor has two compartments of 0.4L separated by a nylon or PTFE microporous membrane. Ion-exchange resins were used as a catalyst under mild conditions with or without glycerol extraction. Water and ethanol were used as the extraction phase. The mass transfer coefficients of the reaction medium components were estimated using a synthetic reaction medium and different extraction phases. The reaction was followed by triglyceride conversion measuring free glycerol and combined glycerol. Triglyceride conversion increased by 18% when using an anionic resin (Amberlyst® A26) and ethanol as the extracting phase. A simplified mass transfer model was developed and applied to simulate the coupled system. The simulated results indicated that a ratio of membrane area to the reactor volume of 2.2cm−1 results in a 97.3% reduction of the glycerol content in the reaction medium. These results demonstrate the potential of coupling transesterification and a membrane contactor by shifting the reaction equilibrium and reducing the purification steps of the process.

Limitations of simple mass transfer models in polydisperse liquid–liquid dispersions

In this work the limitations of standard approaches, commonly used to describe mass transfer in fluid–fluid systems are critically discussed. Emphasis is placed on polydisperse systems, such as liquid–liquid dispersions. In the simplest possible approach the fluid–fluid system is assumed to be monodisperse: namely all the elements of the disperse phase have the same properties. This very simple (albeit inaccurate) approach is the one typically employed for design, scale-up and optimization of unit operations and of the corresponding equipments. The adequacy (or inadequacy) of this model depends on the competition between three phenomena: droplet coalescence, breakage and mass transfer (often enhanced by chemical reactions). When coalescence and breakage dominate, the only polydispersity that has to be accounted for is droplet size, whereas on the contrary, when mass transfer dominates the process, very often polydispersity with respect to both size and chemical composition must be considered. This can be efficiently done by solving the so-called population balance equation with, for example, quadrature-based moment methods. In this work a strategy to evaluate a-priori the complexity of the model to be used, based on time scales, is proposed and tested.

Early stage C-history method: Rapid and accurate determination of the key SVOC emission or sorption parameters of indoor materials

The accurate and rapid determination of the emission parameters of semi-volatile organic compounds (SVOCs) from indoor materials is of great importance for estimating and controlling indoor exposure. By virtue of a simplified mass transfer model we derived, a new method called the early stage C-history method, has been developed to measure the key emission parameters: the gas phase SVOC concentration adjacent to the material surface (y0) and the convective mass transfer coefficient (hm). We validate this model using experimental data found in the literature. When compared with established methods, the new method has the following salient features: (1) rapid (the experimental time is reduced from several months to several days); (2) accurate (R2 in the range of 0.92–0.97). Further analysis shows that both features can be further improved if the test system has a smaller chamber wall/air partition coefficient. The new method is also extended to measure the key parameters of SVOCs from sorption materials. This method should prove useful for screening SVOC emission characteristics and for assessing exposure, as well as for chamber and test design.

Fluorocarbon nanodrops as acoustic temperature probes.

This work investigated the use of superheated fluorocarbon nanodrops for ultrasound thermal imaging and the use of mixed fluorocarbons for tuning thermal and acoustic thresholds for vaporization. Droplets were fabricated by condensing phospholipid-coated microbubbles containing C3F8 and C4F10 mixed at various molar ratios. Vaporization temperatures first were measured in a closed system by optical transmission following either isothermal pressure release or isobaric heating. The vaporization temperature was found to depend linearly on the percentage of C4F10 in the droplet core, indicating excellent tunability under these fluorocarbon-saturated conditions. Vaporization temperatures were then measured in an open system using contrast-enhanced ultrasound imaging, where it was found that the mixed droplets behaved like pure C4F10 drops. Additionally, the critical mechanical index for vaporization was measured at the limits of therapeutic hyperthermia (37 and 60 °C), and again the mixed droplets were found to behave like pure C4F10 drops. These results suggested that C3F8 preferentially dissolves out of the droplet core in open systems, as shown by a simple mass transfer model of multicomponent droplet dissolution. Finally, proof-of-concept was shown that pure C4F10 nanodrops can be used as an acoustic temperature probe. Overall, these results not only demonstrate the potential of superheated fluorocarbon emulsions for sonothermetry but also point to the limits of tunability for fluorocarbon mixtures owing to preferential release of the more soluble species to the atmosphere.

Modifier mass transfer kinetic effect in the performance of solvent gradient simulated moving bed (SG-SMB) process

The solvent-gradient simulated moving bed process (SG-SMB) is the new tendency in the performance improvement if compared to the traditional isocratic solvent conditions. In such SG-SMB separation process the modulation of the solvent strength leads to significant increase in the purities and productivity followed by reduction in the solvent consumption. A stepwise modelling approach was utilized in the representation of the interconnected chromatographic columns of the system combined with lumped mass transfer models between the solid and liquid phase. The influence of the solvent modifier was considered applying the Abel model which takes into account the effect of modifier volume fraction over the partition coefficient. The modelling and simulations were carried out and compared to the experimental SG-SMB separation of the amino acids phenylalanine and tryptophan. A lumped mass transfer kinetic model was applied for both the modifier (ethanol) as well as the solutes. The simulation results showed that such simple and global mass transfer models are enough to represent all the mass transfer effect between the solid adsorbent and the liquid phase. The separation performance can be improved reducing the interaction or the mass transfer kinetic effect between the solid adsorbent phase and the modifier. The simulations showed great agreement fitting the experimental data of the amino acids concentrations both at the extract as well as at the raffinate.

Exergetic simulation of a combined infrared-convective drying process

Optimal design and performance of a combined infrared-convective drying system with respect to the energy issue is extremely put through the application of advanced engineering analyses. This article proposes a theoretical approach for exergy analysis of the combined infrared-convective drying process using a simple heat and mass transfer model. The applicability of the developed model to actual drying processes was proved using an illustrative example for a typical food.

A proposed mathematical model for exergy analysis of an infrared (IR) drying process

In this paper, a new mathematical model was proposed for exergy analysis of an IR drying process. The exergy balance equation was derived based on the IR heating principle and accordingly was applied for determining the exergetic parameters, i.e., exergy destruction and exergy efficiency. A simple heat and mass transfer model was taken into account to ascertain the applicability of the presented model to actual IR drying process at different drying conditions. An illustrative example was numerically solved for a typical food during IR drying process. This model can be offered as an adaptable framework to scrutinise the economical and environmental concerns associated with the application of the IR drying method, to compare the exergetic performance of the IR drying process with the other available drying techniques, to optimise the design of IR drying facilities and their elements and to recognise the suitable applications and optimal configurations for IR drying equipments.

Leakage of central venous catheter locking fluid by hemodynamic transport.

Central venous catheters are often filled when not in use with an anticoagulating fluid, usually heparinized saline, known as the locking fluid. However, the use of the locking fluid is associated with known risks because of "leakage" of the lock. A new hypothesis is proposed here to explain the lock fluid leakage: that the leakage is due to advective and diffusive mass transfer by blood flow around the catheter tip in situ. On the basis of previous in vitro experiments, the leakage mechanism has been hypothesized to be fluid motion driven by buoyancy forces between the heavier blood and the lighter locking fluid. The current hypothesis is justified by a simple one-dimensional mass transfer model and more sophisticated three-dimensional computational hemodynamic simulations of an idealized catheter. The results predict an initial, fast (<10 seconds) advection-dominated phase, which may deplete up to 10% of the initial lock, followed by a slow diffusion-limited phase which predicts an additional 1-2% of leakage during a 48 hour period. The current results predict leakage rates that are more consistent with published in vivo data when compared with the buoyancy hypothesis predictions, which tend to grossly overestimate leakage rates.

Surface engineering characteristics of ultrasound assisted hypophosphite electroless plating baths

This article addresses the characteristics of metallic skin layer and the performance of hypophosphite based ultrasonic electroless plating baths during the fabrication of nickel/ceramic microfiltration membranes. The process performance was evaluated in terms of overall conversion and metal plating efficiency, and the metal film was characterised in terms of average film pore size, average effective porosity, film thickness and per cent pore densification. Parametric investigations were carried out for a wide range of initial nickel solution concentrations (0·04–0·16 mol L−1) at two different loading ratios (196 and 393 cm2 L−1) for sonication coupled electroless plating. A simple mass transfer model was developed to provide insights with respect to the pertinent mass transfer limitations. Sonication resulted in faster deposition rate, better efficiency and improved surface morphology. In comparison with conventional and agitated electroless plating baths, ultrasound assisted electroless plating provided the best combination of process as well as performance characteristics.

Densification and microstructure evolution during sintering of silicon under controlled water vapor pressure

Abstract Sintering of fine silicon powder was studied under controlled water vapor pressures using the Temperature–Pressure–Sintering Diagram approach. The water vapor pressure surrounding the sample was deduced from thermogravimetric analysis and related to the water content of the incoming gas flux with a simple mass transfer model. The thickness of the silica layer covering silicon particles was then monitored by the water vapor pressure and the microstructure evolution and densification during sintering could be controlled. Stabilizing the silica layer indeed inhibits grain coarsening and allows better densification of the compacts under humidified atmosphere as compared to dry atmosphere.

Simple model of mass transfer in template synthesis of metal ordered nanowire arrays

A simple model of electrochemical growth of nanowires in the pores of anodic aluminum oxide (AAO) template is developed. The metal deposition is considered at various overpotentials. The model takes into consideration the ionic transfer both in the varying diffusion layer in the pores and in the diffusion layer above the template, which is determined by the external hydrodynamic conditions. The model takes into account the kinetics of electrochemical reaction by means of the Tafel equation and the diffusion transfer of metal cations both in the pores and in the outer diffusion layer. The analytical solution of the problem with several simplifications yields the equations for calculating the time dependence of current, the pore filling time, and other parameters of the process. An example of the application of the model for the analysis of nanowire growth in the template pores is compared with the experimental data showing good agreement.