Determination Of Mass Transfer Coefficients Research Articles

Mass transfer of dissolved oxygen using rotating cylinder electrode under bulk boiling conditions

The mass transfer behavior of oxygen and ferricyanide in dilute aqueous solutions was investigated using a rotating cylinder electrode under bulk boiling condition. A correlation was developed for predicting the mass transfer behavior using the reaction of dissolved oxygen below boiling condition. This correlation was used to predict the mass transfer behavior for ferricyanide reaction from room temperature to just below boiling point (i.e. 99°C) for the rotating speeds between 100 and 3300rpm. These results indicated that the ferricyanide reaction could be used as a model to predict the electrochemical behavior of dissolved oxygen at the elevated electrolyte temperatures. However, the correlation could not predict the experimental data obtained under boiling conditions very well. The experimentally determined mass transfer coefficients under boiling condition were on the average 38% higher than those obtained just below boiling point due to the generation and rupture of boiling bubbles in bulk solution.

Effect of CaO Addition on Iron Recovery from Copper Smelting Slags by Solid Carbon

We investigated the effect of flux (lime) addition on the reduction behavior of iron oxide in copper slag by solid carbon at 1773 K (1500 °C). In particular, we quantified the recovery of iron by performing typical kinetic analysis and considering slag foaming, which is strongly affected by the thermophysical properties of slags. The iron oxide in the copper slag was consistently reduced by solid carbon over time. In the kinetic analysis, we determined mass transfer coefficients with and without considering slag foaming using a gas holdup factor. The mass transfer of FeO was not significantly changed by CaO addition when slag foaming was ignored, whereas the mass transfer of FeO when slag foaming was considered was at a minimum in the 20 mass pct CaO system. Iron recovery, defined as the ratio of the amount of iron clearly transferred to the base metal ingot to the initial amount of iron in the slag phase before reduction, was maximal (about 90 pct) in the 20 mass pct CaO system. Various types of solid compounds, including Mg2SiO4 and Ca2SiO4, were precipitated in slags during the FeO reduction process, and these compounds strongly affected the reduction kinetics of FeO as well as iron recovery. Iron recovery was the greatest in the 20 mass pct CaO system because no solid compounds formed in this system, resulting in a highly fluid slag. This fluid slag allowed iron droplets to fall rapidly with high terminal velocity to the bottom of the crucible. A linear relationship between the mass transfer coefficient of FeO considering slag foaming and foam stability was obtained, from which we concluded that the mass transfer of FeO in slag was effectively promoted not only by gas evolution due to reduction reactions but also by foamy slag containing solid compounds. However, the reduced iron droplets were finely dispersed in foamy and viscous slags, making actual iron recovery a challenge.

Supersonic Lance Mass Transfer Modelling

Numerical models of steelmaking processes are essential tools for process development and optimisation. A usable model is detailed enough to provide reliable results and not to slow to run. In order to make a fast and accurate model of a single process, all model parameters must be known well. This can be achieved by first simulating detailed models from which the parameters are obtained.In many converter processes oxygen is delivered into melt by supersonic top lance blowing. When such process is modeled, a model describing mass transfer from the lance into melt surface is needed.This paper describes numerical modeling of mass transfer by supersonic lances. Lance flow CFD models are used to determine mass transfer coefficients for typical lance applications. Models are validated with supersonic nozzle data and wall impinging jet mass transfer data from literature. The results are later used in fast process simulation models.

Extended Model for Theoretical Determination of Mass Transfer Coefficients in Multiphase Flows – Part 2

AbstractDie Auslegung von Reaktoren mit Mehrphasensystemen und chemischer Reaktion stellt auch heute noch eine Herausforderung dar. Neue, erweiterte Erkenntnisse über die in Mehrphasenströmungen auftretenden örtlichen Transportprozesse weisen vielversprechende Optionen in Hinblick auf eine theoretische Abschätzung von Stoffübergangskoeffizienten auf. Ein auf den neuen Erkenntnissen basierender Modellansatz zur Berechnung des Stofftransportkoeffizienten wurde im ersten Teil dieser Veröffentlichung aufgezeigt und wird im vorliegenden Artikel hinsichtlich der Relevanz für die praxisrelevante Auslegung von Treibstrahl‐Schlaufenreaktoren überprüft.

PEMFC GDE Oxygen Mass Transport Coefficient Separation with Different Gas Diluents

A parametric current distribution model is proposed for the overall PEMFC reactant mass transfer coefficient determination. The model was derived for a dilute reactant stream and a low cell voltage (limiting current). Separation of the mass transfer coefficient into gas and ionomer phase components is achieved with similar current distribution measurements completed with different molecular mass diluents. An extrapolation to a diluent with zero molecular mass leads to the ionomer phase mass transfer coefficient. The gas phase mass transfer coefficient is subsequently calculated using an additive relationship between the overall mass transfer coefficient and its components (gas and ionomer phase coefficients). Experimental measurements demonstrate the validity of the current distribution model and emphasize the need to use dilute reactant streams to facilitate data treatment.

Determination of Mass Transfer Coefficients for A Mixture of Compost, Sugarcane Bagasse, and Granulated Activated Carbon as Packing Medium in Biofilter

ABSTRACT A laboratory-scale biofilter unit packed with a mixture of compost, sugarcane bagasse, and granulated activated carbon (GAC) in the ratio of 55:30:15 by weight was used for a biofiltration study of air stream containing benzene, toluene, ethylbenzene, and o-xylene (BTEX). The effect of superficial velocity on mass transfer coefficient for the packing was studied by maintaining gas flow rates of 3, 4, 5, 6, and 8 L min−1 for inlet concentrations of 0.1, 0.4, and 0.8 g m−3 for each of benzene, toluene, ethylbenzene, and o-xylene. The maximum elimination capacity was found to be 20.92, 22.72, 20.73, and 18.94 g m−3 h−1 for BTEX, respectively, for stated flow rates. Removal efficiency of BTEX decreased from 99% to 71% for increasing inlet concentration from 0.1 to 0.8 g m−3. Gas film mass transfer coefficient predicted by modified Onda's equation was within ±10% of the experimental values.

Experimental determination of mass transfer coefficients of volatile sulfur odorants in biofilter media measured by Proton-Transfer-Reaction Mass Spectrometry (PTR-MS)

Mass transfer from air to the liquid phase is an important process that may limit the efficiency of biological air filters used for abatement of odor from livestock production facilities. Mass transfer limitation is especially important for volatile sulfur compounds with relatively low aqueous solubility. A better understanding of limitations of mass transfer is therefore important in order to enhance the performance and design of biofilters. In this study, a method based on Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) has been developed in combination with a developed model to determine the mass transfer coefficients of volatile sulfur compounds for selected packing material used in biofilters. PTR-MS was used to measure breakthrough curves for sulfur compounds with adequate sensitivity, time resolution and reproducibility. The overall mass transfer coefficient for the selected biofilter media was then estimated by fitting an advection–dispersion equation modified for mass transfer between the gas and liquid phases to the measured profile of individual sulfur compound. Different injection strategies were evaluated and an optimal measurement procedure was developed. The method was validated by comparison of mass transfer coefficients to literature values for toluene, which was used as a reference compound in this study. By applying the method to compounds with different Henry’s law constants, the application range of the method was demonstrated regarding solubility in water. This study demonstrates a method for determination of mass transfer coefficients of sparingly soluble gaseous compounds for selected biofilter media by applying PTR-MS in combination with modeling.

Extended Model for Theoretical Determination of Mass Transfer Coefficients in Multiphase Flows – Part 1

AbstractDie Auslegung von Reaktoren mit Mehrphasensystemen und die Steuerung überlagerter chemischer Reaktionen stellen auch heute noch Herausforderungen dar. Neuere, erweiterte Erkenntnisse zur Charakterisierung der Meso‐Ebene in Mehrphasenströmungen weisen vielversprechende Optionen in Hinblick auf eine theoretische Abschätzung von Stoffübergangskoeffizienten auf. Bestehende Modellansätze sind bisher nur für enge Anwendungsbereiche der Mehrphasenströmung gültig. Welche Möglichkeiten sich durch eine, auf den neuen Erkenntnissen basierende Zusammenführung der Modelle für die zukünftige Modellierung und die Berechnung des Stofftransportes ergeben, wird in dem vorliegenden Artikel aufgezeigt.

Mass transfer coefficient determination in three biphasic systems (water–ionic liquid) using a modified Lewis cell

Baeyer–Villiger bioconversion productivity of the cyclic ketone (±)-cis-bicyclo [3.2.0] hept-2-en-6-ona by the biocatalyst Escherichia coli TOP10 pQR239 in a multiphase system can be limited by mass transport. Mass transfer rates through the liquid–liquid interface depend on the volumetric mass transfer coefficient (kA) and the substrate and product partition coefficients. In situ experimental determination of the volumetric mass transfer coefficient in a partitioning bioreactor is complex. In this work, the substrate (kS) and product (kP) global mass transfer coefficients were determined in a modified Lewis cell in three water–ionic liquids systems. The ionic liquids used were butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide [MeBuPyrr][BTA], trioctylmethylammonium bis(trifluoromethylsulfonyl)imide [OMA][BTA] and 1-butyl-3-metyl-imidazolium hexafluorophosphate [BMIM][PF6]. The maximum kS and kP values obtained were 4.35×10−5 and 1.21×10−5ms−1 for water-[MeBuPyrr][BTA] system; 1.53×10−5 and 7.84×10−6ms−1 for water-[OMA][BTA] system, respectively; and kS values up to 1.01×10−5ms−1 were found for the water-[BMIM][PF6] system. The association among the mass transfer coefficients and the physicochemical properties (interfacial tension, viscosity and density) and the thermodynamics (partition coefficients) are analysed and discussed. Finally, the volumetric mass transfer coefficients (kSA and kPA) were calculated using interfacial areas (A) of the dispersed ionic liquid phase estimated from the “Sauter” mean drop diameter (d32) in a one litre stirred tank partitioning bioreactor.

A NOVEL METHODOLOGY TO MEASURE MASS TRANSFER AROUND A BUBBLE

An original approach for accurately measuring the mass transfer of a single bubble rising in a liquid is reported. The approach consists in using PLIF technique (Planar Laser Induced Fluorescence) at micro-scale to capture images of the released oxygen concentration field in the bubble wake. The applicability of the technique for determining mass transfer coefficients in different fluids (1 < Re < 100) is demonstrated and the relevance of the results is corroborated by established correlations. This direct and non-intrusive technique could be a promising tool to enrich the understanding of mass transfer phenomena.

Preliminary characterization of carbon dioxide transfer in a hollow fiber membrane module as a possible solution for gas–liquid transfer in microgravity conditions

In microgravity, one of the major challenge encountered in biological life support systems (BLSS) is the gas–liquid transfer with, for instance, the necessity to provide CO 2 (carbon source, pH control) and to recover the evolved O 2 in photobioreactors used as atmosphere bioregenerative systems. This paper describes first the development of a system enabling the accurate characterization of the mass transfer limiting step for a PTFE membrane module used as a possible efficient solution to the microgravity gas–liquid transfer. This original technical apparatus, together with a technical assessment of membrane permeability to different gases, is associated with a balance model, determining thus completely the CO 2 mass transfer problem between phases. First results are given and discussed for the CO 2 mass transfer coefficient k L CO 2 obtained in case of absorption experiments at pH 8 using the hollow fiber membrane module. The consistency of the proposed method, based on a gas and liquid phase balances verifying carbon conservation enables a very accurate determination of the k L CO 2 value as a main limiting step of the whole process. Nevertheless, further experiments are still needed to demonstrate that the proposed method could serve in the future as reference method for mass transfer coefficient determination if using membrane modules for BLSS in reduced or microgravity conditions.

Mass transfer of chlorobenzene in concentrated sulfuric acid

Mass transfer of chlorobenzene in sulfuric acid is very important in the nitration of chlorobenzene by mixed acid. This article presents the determination of mass transfer coefficient at high-concentrations of sulfuric acid at 298 K and 313 K at 2 π rad/s and 4 π rad/s impeller speeds. The experiments were carried out under flat-interface conditions in an unbaffled glass reactor of 10 cm diameter and 1 dm 3 capacity. A glass stirrer with two paddle-type impellers was employed for stirring. The upper paddle stirred the organic phase and the lower paddle stirred the aqueous phase. High mass transfer coefficients were obtained at high-concentrations of sulfuric acid. Dynamic light scattering of the aqueous phase revealed that a dispersion of chlorobenzene spontaneously formed in sulfuric acid, which is believed to be the main factor behind the high mass transfer coefficient. NMR analysis of the aqueous phase showed that no chemical reaction occurred at 298 K and 313 K, but some amount of 4-chlorobenzenesulfonic acid formed at 323 K. The high mass transfer coefficient is expected to result in high yield of chloronitrobenzenes at moderate temperatures and low stirring speeds.

Statistical Rate Theory Insight into Evaporation and Condensation in Multicomponent Systems

Current approaches to mathematically modeling liquid-vapor mass transport (e.g., film theory, penetration theory, boundary layer theory) treat bulk phase transport accurately with diffusion models, but leave the transport across the interface to be described by empirically determined mass transfer coefficients. In multicomponent systems, this requires empirical mixing rules for the single-component mass transfer coefficients. Such approaches can only give estimates of net rates at the interface but cannot examine the movement of individual components. Here we use statistical rate theory to provide new physical insight into evaporation and condensation at interfaces in systems containing multiple volatile components. In contrast to the traditional multicomponent mass transfer approach, we show ranges where one component evaporates while the other condenses even when the net transport is unidirectional.

Peritoneal Inflammation after Twenty-Week Exposure to Dialysis Solution: Effect of Solution versus Catheter–Foreign Body Reaction

We hypothesized that both sterile solutions and foreign body reaction to the peritoneal dialysis catheter are associated with inflammatory changes in rats exposed to hypertonic solution. Four hypertonic solutions (30 - 40 mL) were injected daily via needle and syringe over 20 weeks in 4 groups of rats: 4.25% standard clinical solution (LAC), LAC plus pyridoxamine (PYR), LAC plus ethyl pyruvate (EP), and a biocompatible 4% dextrose solution (BIC). Two groups received catheters: a non-injected 4-week catheter group (C4) and a group injected for 20 weeks with the BIC solution (CI). Control animals (CON) were not injected. In the C4 group, adherent cells were separated from the catheter and examined by culture and electron microscopy to ensure that animals were bacteria free prior to exposure to solution. Animals underwent transport experiments to determine mass transfer coefficients of mannitol (MTC(M)) and albumin (MTC(A)), osmotic filtration flux (J(osm)), and hydrostatic pressure-driven flux (J(p)). After euthanasia, tissues were examined for submesothelial thickness, vascular density, and immunohistochemistry for various cytokines. The catheter cell layer was free of bacteria and consisted of macrophages, lymphocytes, mesothelial cells, and fibroblastic cells. Marked differences in angiogenesis and submesothelial thickening were noted for the catheter groups. Transport differences were mixed: MTC(M) was significantly less for the CI group and MTC(A) was variable among the groups. There were no differences among groups for J(osm) or J(p). Inflammatory markers in the catheter-adherent cells correlated with inflammatory changes in the tissue. These data demonstrate significant changes in submesothelial thickness, angiogenesis, transport function, and inflammatory markers between animals injected with sterile solutions over 20 weeks with and without catheters. An indwelling catheter amplifies peritoneal inflammation from dialysis solutions through a foreign body reaction. Our data also suggest that additives to existing solutions may have limited the effect on inflammatory response to non-biocompatible solutions.

Hydrodynamic analogy approach for modelling of reactive stripping with structured catalyst supports

Modelling of gas/vapour–liquid separation processes usually requires experimentally determined parameters, e.g., mass transfer coefficients. This results in expensive experimental work, especially for new types of column internals. A novel modelling approach based on hydrodynamic analogies (HA) has recently been developed for distillation units equipped with structured corrugated sheet packings. The HA model takes the packing geometry directly into account whereas the experimental determination of mass transfer coefficients is not required. In this work, the HA approach is extended to cover heterogeneously catalysed reactive stripping processes. Experimental investigations are performed with a test system, esterification of hexanoic acid and 1-octanol, using different types of catalytically coated supports as column internals (one corrugated sheet packing and three film-flow monoliths with different channel geometries). Simulation results obtained with the extended HA model are in a good agreement with experimental values.

Convective Mass Transfer Coefficients for Gypsum and Wood Paneling

Abstract This paper presents the measured convective mass transfer coefficients for humid air flowing above an initially dry gypsum and wood panel (equilibrium with 30 % RH air) in the transient moisture transfer (TMT) facility at the University of Saskatchewan. The convective coefficients are measured during laminar flow at three different Reynolds numbers (Re=800, 1500, and 2100) and with three different humidities in the air stream (50, 70, and 90 % RH). The results show that the measured mass transfer coefficients are lower than the values measured above an open water surface by Iskra and Simonson in a previous work. For gypsum, the convective mass transfer coefficient varies from 0.0016 to 0.0033 m/s (1.2×10−8 to 2.4×10−8 s/m) with 95 % confidence uncertainty bounds ranging from ±20 to ±57 %. For wood, the convective mass transfer coefficient varies from 0.0001 to 0.0008 m/s (9.4×10−10 to 5.7×10−9 s/m) with 95 % confidence uncertainty bounds ranging from ±50 to±300 %. The experimental data are analyzed with a 1-D heat and mass transfer numerical model to check the discrepancy with the experimental data. The uncertainty associated with an indirect determination of mass transfer coefficient is discussed.

Development of an approximate empirical-CFD model estimating coupled heat and water transfers of stacked food products placed in airflow

This paper reports on the development of an approximate empirical-CFD modelling procedure combining experimental correlations for the heat and mass transfer coefficient determination and specific user-defined functions (UDF) implemented in the commercial CFD code Fluent to simulate the interrelationships at play between airflow and transfers of unwrapped food products bathing in air. Transfer modelling required specific calculation to account for water evaporation from the product surface. Mean transfer coefficients at the air–product interface were determined empirically from validated experimental correlations, where the CFD mean air velocity that is calculated in a small user-defined volume surrounding the product was incorporated. Internal water diffusion was taken into account by considering the product as a motionless fluid composed of dry matter and water. The procedure developed allows, in a single CFD calculation using a single mesh, temperature and water concentration fields to be computed and the water loss kinetics of the products to be determined together with the temperature and relative humidity fields of the air flowing around them. Although the established procedure was set up with the aim of assessing heat and water exchanges occurring in large stacks of unwrapped food products subjected to airflow, this last was validated for modelling, first, one-dimensional drying of a meat cylinder and second, three-dimensional drying of five cylindrical plaster casts placed in a row. Its application to the ripening of a row of six cheeses is also discussed.

Determination of mass transfer coefficients for packing materials used in biofilters and biotrickling filters for air pollution control—2: Development of mass transfer coefficients correlations

Correlations that allow determination of gas film mass transfer coefficients ( k G a t , k G a w ) and liquid film mass transfer coefficients ( k L a w ) for packing materials used in biofilters and biotrickling filters for air pollution control are presented. Lava rock, polyurethane foam cubes (PUF), Pall rings, porous ceramic beads, porous ceramic Raschig rings, and various compost–woodchips mixtures were used as packing materials. The functionality of gas and liquid velocity on mass transfer coefficients ( k G a t , k G a w , k L a w ) obtained experimentally (see Part 1 of this paper) was correlated using modified Onda-type equations. The correlation equations helped to better understand the sensitivity of gas and liquid velocities on mass transfer, and the effects of packing wetting. Each packing had a different functionality with gas and liquid velocity and different wetting property, hence different correlation equations were needed for the different packing materials. Most of the fitted data fell within ± 20 % of the experimental values.

Determination of mass transfer coefficients for packing materials used in biofilters and biotrickling filters for air pollution control. 1. Experimental results

Gas film mass transfer coefficients ( k G a t , k G a w ) and liquid film mass transfer coefficients ( k L a w ) for packing materials used in biofilters and biotrickling filters for air pollution control were determined experimentally. Lava rock, polyurethane foam cube (PUF), Pall ring, porous ceramic beads, porous ceramic Raschig rings and compost–woodchips mixtures were investigated. The experiments were performed at gas velocities ranging from 100 to 8000 m h - 1 and liquid velocities of 0.1 – 12 m h - 1 , i.e., a wide range that covers most biofilters and biotrickling filters. k G a t in biofilter packings ranged from about 500 to 2500 h - 1 , while k G a w and k L a w in biotrickling filters ranged from 100 to 8000 h - 1 , and 1 to 300 h - 1 , respectively, depending on the packings and the conditions. This is markedly lower than mass transfer coefficients usually observed for conventional wet scrubbing. The gas film mass transfer coefficient ( k G a t ) of 50:50% vol compost–woodchips mixture, a common biofilter packing, was greater than this of a 20% vol compost and 80% woodchips mixture, though the mass transfer was not increased by increasing further the volume fraction of compost. All compost mixtures exhibited a greater gas film mass transfer coefficient than lava rock or other synthetic materials. The mass transfer coefficients of compost mixtures was also influenced by packing method and it was directly proportional to the surface area of the bulking agents added. The gas film mass transfer coefficient ( k G a w ) of five biotrickling filter packing materials increased linearly with gas velocity. The effect of liquid on the gas film mass transfer coefficient was not significant. Of all the biotrickling filter packings, the porous ceramic beads had the highest gas and liquid film mass transfer coefficients followed by lava rock, porous ceramic rings, 1 in Pall ring and PUF cubes. The liquid film mass transfer coefficient ( k L a w ) was directly proportional to liquid velocity and the effect of gas velocity was negligible. Several correlations allowing prediction of mass transfer coefficients are presented in Part 2 of this paper.

NOM removal by adsorption onto granular ferric hydroxide: Equilibrium, kinetics, filter and regeneration studies

Adsorption onto granular ferric hydroxide (GFH) with subsequent in-situ regeneration is studied as a new process for natural organic matter (NOM) removal from groundwater. Adsorbent equilibrium loadings of 10–30 mg DOC g −1 GFH −1 are obtained, whereas the non-adsorbable DOC fraction amounts to 1.5 mg L −1 for all investigated groundwaters. The larger and UV-active NOM fractions (mainly fulvic acids) are well adsorbed while the smaller molecular fractions are poorly or not adsorbed. However, kinetic studies show that the smaller and medium-sized fulvic acids are removed first. The equilibrium is strongly dependent on pH but only weakly on ionic strength, pointing to ligand exchange as the dominant adsorption mechanism. With regard to NOM structure, prerequisites for adsorption onto GFH are both a minimum number of functional groups and a molecular size small enough to enter the GFH pores. NOM breakthrough curves are successfully simulated using the LDF model (homogeneous surface diffusion model (HSDM) with linear driving force approach for surface diffusion) and experimentally determined mass transfer coefficients. Regeneration of loaded GFH is possible either by use of NaOH or oxidatively by H 2O 2. The optimal quantities and concentrations are determined.