Mass Transfer Data Research Articles

Intensification of the rate of heat and mass transfer in a batch and continuous parallel plate contactor by pulsed flow

The effect of pulsating flow on the rate of mass transfer in a parallel plate reactor was studied by the electrochemical technique. For batch reactor, pulsating flow increased the rate of mass transfer compared to natural convection by a factor ranging from 1.05 to 2.43. A mathematical model was developed to prove that surface renewal plays a major role in enhancing the rate of mass transfer at high pulsation velocities. The combination of steady flow and pulsating flow increased the rate of mass transfer by a factor ranging from 9 to 17 under steady laminar flow and from 3 to 4 in case of turbulent steady flow. Mass transfer data were correlated for batch and continuous reactors by dimensionless correlations. Applications of the present correlations in the design and operation of parallel plate contactors such as electrochemical reactors, heat exchangers, catalytic reactors, and membrane equipment were discussed.

Electro Winning from Dilute Solutions at Enhanced Rates using Three-Phase Flow Reactor

Enhancement of mass transfer coefficient is highly desirable for economic design of process equipment. The present study is essentially carried out to know the effect of flow variables such as gas and liquid velocities and geometric parameters of the internal on mass transfer coefficients in a three phase fluidized bed. The mass transfer coefficient data were obtained using a string of cones internal in a three-phase fluidized bed electrochemical reactor. The flow system investigated was nitrogen, a fluid electrolyte and spherical glass beads as gas, liquid and solid phases respectively. Limiting current technique was employed to obtain mass transfer data. The internal comprises of a string of cones arranged concentrically on a central rod which is placed coaxially in a three phase fluidized bed. The presence of internal in three phase fluidized beds augmented the mass transfer coefficient significantly. In the present investigation it was found that the effect of gas velocity, liquid velocity, rod diameter and cone diameter was only marginal. However, the influence of pitch, half apex angle of cone and particle diameter was found to be significant. Correlations were developed based on least squares regression analysis for the prediction of mass transfer coefficient in terms of pertinent variables.

TransPoly: A theoretical model to quantify the dynamics of water transfer through nanostructured polymer films

Mass transfer of penetrants is among the most important physical properties of polymer films to properly ensure function during service. In the case of interaction between penetrants and polymer, non-Fickian diffusion can be observed. This phenomenon is described by numerous reports and a few models have been proposed. Nevertheless, few of them quantify Fickian and non-Fickian behaviour using parameters with clear physical meaning. The present work develops a new non-Fickian mass transport model: TransPoly (Transfer through Polymers). Based on coupled heat and mass transfer, it accounts for simultaneous Fickian transport and molecular relaxation. This model is applied to data of water vapour mass transfer in nanocomposites of polylactide and cellulose nanocrystals. The contribution of the non-Fickian mass transfer on water vapour sorption is highlighted. TransPoly can be applied to several kinds of polymers and used for prediction purposes once the parameters are determined on a learning database.

Effect of drag reducing polymers and impeller geometry on the rate of mass and heat transfer at the wall of a cylindrical stirred tank reactor in relation to catalytic reactor design

The effect of impeller geometry on the rate of liquid-solid mass transfer at the wall of the stirred tank reactor was studied by measuring the rate of the diffusion-controlled disintegration of copper in acidified dichromate. Factors examined were rotation speed of impeller and its geometry, drag reducing polymer concentration, solution physical properties and baffles effect. The mass transfer data in the blank solution were correlated by dimensionless correlations. Radial flow impellers produced higher rates of mass transfer than axial flow impellers under the same conditions. For a given set of conditions the presence of baffles was found to increase the rate of mass transfer more than unbaffled reactors. Drag reducing polymer was found to decrease the mass transfer rate by an amount ranging from 3.5 to 38.5% depending on rotation speed of impeller, polymer concentration and impeller geometry. Implication of the present results for stirred tank biochemical reactors which use drag reducing polymer to control solution viscosity and decrease the shear stress between the moving solution and the vessel wall as to protect immobilized enzyme or cells fixed to the wall against mechanical damage were discussed. The present results would help in evaluating the financial possibility of utilizing drag reducing polymers in working biochemical stirred tank reactors.

Mass transfer evaluation in a multi-impeller extractor for reactive Mo (VI) extraction from aqueous Sulphate solution by utilizing coupling of acid and solvating Extractants

In this study, mass transfer experimental data from the present column with 70 cm active column length and 11.3 cm internal diameter were interpreted for molybdenum extraction with a mixture of D2EHPA and TBP in terms of the axial diffusion model. The influence of extractants concentration and the initial aqueous pH have studied in the bench-scale experiments. The experimental finding demonstrated that the synergistic solvent extraction increases the constancy of the extracted complexes for transfer into the organic phase. The effect of operating parameters, including agitation speed and inlet phase velocities on the overall mass transfer coefficients under the chemical reaction system, is discussed. By considering the reactive extraction system in this column, the results showed that the overall mass transfer coefficients increase with an increase in the agitation speed and inlet phase velocities. It was also found that the column performance is significantly dependent on agitation speed and dispersed phase velocity. However, it slightly depends on the continuous phase velocity. The experiments for solvent extraction processes have performed to obtain the concentration profile along the column in both the aqueous and organic phases as a function of the operating conditions. The available models for the prediction of mass transfer performance were studied, and their predictions have compared with the present mass transfer data. Because of the column geometry and chemical reaction condition, the available empirical models failed to predict the mass transfer data accurately. Therefore, a new correlation had developed to predict the enhancement factor. The values calculated by the proposed model had compared with the experimental data, and a good agreement between them had obtained.

Reconciliation of gas to liquid mass transfer in parallel and transverse flow (cross-flow) hollow fiber membrane contactors (HFMC) for CO2 absorption

ABSTRACT Previous studies have found difficulties in reconciling mass transfer between membrane contactors of different geometries, which has been attributed to differences in fluid mixing. In this study, we compare the two most commonly adopted geometries (parallel and transverse flow) and use residence time distribution (RTD) analysis to verify the influence of geometry on fluid mixing in addition to developing a generalized correlation that can collectively describe mass transfer for both geometries. Lumen-side mass transfer was well described by the Lévêque solution in well-developed laminar conditions for both parallel and transverse flow modules. However, considerably lower mass transfer was identified for shell-side flow in the parallel fiber configuration, with RTD analysis providing confirmation that this was due to shell-side bypass which reduced mean fluid residence time in the contactor to below that of the theoretical residence time. The mean residence time calculated from RTD analysis enabled reconciliation of mass transfer data between both geometries, such that mass transfer could be adequately described for both configurations using: . The Reynolds number exponent indicated transitional mass transfer despite operation firmly within the laminar regime, which would indicate an enhancement in mass transfer provided by secondary flow effects within tightly packed fiber bundles. Whilst previously observed, for example in heat transfer analogies, such dependencies are generally more closely associated with parallel flow rather than ‘classical’ cross-flow modules in which fluid flow is explicitly perpendicular to the fiber bundle, and indicates that mass transfer in transverse flow may be better described as parallel flow, which confirms previous assumptions. Importantly, this study demonstrates the capability to reconcile mass transfer between modules of different geometries and permits the opportunity to project process design and scale-up between the two most commonly applied membrane contactor module geometries.

Density, Viscosity, and Physical CO2 Diffusivity of Novel Formulated Solvent N-Methyl-4-Piperidinol and 2-Amino-2-Methyl-1-Propanol for Carbon Capture

Amine based CO2 capture is considered as one of the most effective technologies for mitigating global warming and climate change problems. The key of this technology is to use as highly effective solvent. In the present work, novel formulated MPDL-AMP solvent has been firstly introduced. Its essential data for determining and investigating the solvent performance as an alternative solvent for capturing CO2 has not yet been reported. Therefore, density, viscosity, and physical CO2 diffusivity of novel formulated MPDL-AMP solvent were determined in this work over ranges of concentrations and temperatures of 25%wt. MPDL/5%wt. AMP to 15%wt. MPDL/15%wt. AMP and 313 K to 333 K, respectively. The physical data reported in the present work are important for determining the optimum hydrodynamics of the fluid flow inside the absorption column as well as designing the height of the column through the kinetics and the mass transfer data. The results observed in the present work showed that the novel formulated MPDL-AMP solvent should be further investigated for its potential to be used as an alternative solvent for capturing CO2.

Study of mass transfer correlations for rotating packed bed columns in the context of solvent-based carbon capture

The application of rotating packed beds (RPBs) in solvent-based carbon capture processes, will greatly reduce the physical footprint, capital and operating cost of the process. However, in designing RPBs, correlations for predicting mass transfer parameters are generally limited in literature and their prediction accuracies have not been demonstrated independently. In this paper, an RPB absorber model was developed in gPROMS ModelBuilder® and used to test and compare different correlations for predicting the effective interfacial area, liquid and gas film mass transfer coefficients. Our results showed that the modified packed column mass transfer correlations where the “g” term (i.e. gravitational acceleration) is replaced with “rw2” (i.e. centrifugal acceleration) commonly used in literature for RPBs generally give poor predictions compared to using correlations developed specifically for RPBs. Also, the Tung and Mah correlation has better predictive accuracy for the liquid film mass transfer coefficient in RPBs than more complex correlations. Finally, a set of new data for the gas film mass transfer coefficient for RPBs were also derived from overall volumetric mass transfer coefficient (KGa) experimental data from literature. This is the first report of gas film mass transfer data for RPBs. The results in this paper will guide researchers in selecting suitable correlations for predicting mass transfer parameters in RPBs.

Numerical and experimental investigation of thermo-fluid flow and element transport in electromagnetic stirring enhanced wire feed laser beam welding

The introduction of electromagnetic stirring to laser beam welding can bring several beneficial effects e.g. element homogenization and grain refinement. However, the underlying physics has not been fully explored due to the absence of quantitative data of heat and mass transfer in the molten pool. In this paper, the influence of electromagnetic stirring on the thermo-fluid flow and element transport in the wire feed laser beam welding is studied numerically and experimentally. A three-dimensional transient heat transfer and fluid flow model coupled with dynamic keyhole, magnetic induction and element transport is developed for the first time. The results suggest that the Lorentz force produced by an oscillating magnetic field and its induced eddy current shows an important influence on the thermo-fluid flow and the keyhole stability. The melt flow velocity is increased by the electromagnetic stirring at the rear and lower regions of molten pool. The keyhole collapses more frequently at the upper part. The additional elements from the filler wire are significantly homogenized because of the enhanced forward and downward flow. The model is well verified by fusion line shape, high-speed images of molten pool and measured element distribution. This work provides a deeper understanding of the transport phenomena in the laser beam welding with magnetic field.

(Invited) Thoughts on the Viscous Sublayer

Years ago people postulated that there is a laminar sublayer near a solid wall in turbulent flow. Murphree (1932) and Levich (1942, 1944) postulated that the turbulence eddies decay only gradually as the solid wall is approached. There are two schools of thought: one says that the eddy diffusivity is proportional to y 3 near the wall; the other says y 4. Which is right? Perhaps there is some truth in both views. It may be that y 4 prevails near the outer limit of the viscous sublayer, adjacent to the outer turbulent flow, but that y3 prevails very close to the wall. It has been thought that this was important only for mass transfer in turbulent flow at high Schmidt numbers, that is, for diffusion coefficients much smaller than the kinematic viscosity. However, it is shown that Nikuradse’s data (1932) for pressure drops (or friction factors) in turbulent pipe flow do not agree with his very careful measurements of profiles of the eddy viscosity. In other words, the viscous sublayer cannot be ignored even in fluid flow. The profile of predicted eddy diffusivity of Wasan, Tien, and Wilke (1963) show regions of y 3 dependence very close to the wall and y dependence in the outer turbulent flow with perhaps a y 4 dependence in the intermediate region. On this diagram, one can identify the thickness of the diffusion layer as a function of the Schmidt number. As is well known, the diffusion layer gets very thin at high Schmidt numbers. Using this profile, one can show that the y 4 dependence will not show up clearly in mass-transfer data at any Schmidt number. Any region of y 4 dependence of the eddy diffusivity is outside the diffusion layer where the concentration does not change (at high Schmidt numbers). These thoughts inspire a method of calculating the profiles of eddy diffusivity and eddy viscosity from consideration of fluctuations themselves. Hopefully this can be a subject of future work.

Kinetics of CO2 Absorption in Novel Tertiary N-Methyl-4-Piperidinol Solvent

In the present work, the reaction kinetics of CO2 absorption into aqueous solutions of novel N-methyl-4-piperidinol (MPDL) was experimentally determined in a stirred cell reactor over a MPDL concentration range of 0.5-2.0 M and a temperature range of 303-333 K. Based on the pseudo-first order assumption, a drop of pressure technique was used to extract the reaction rate constant, in terms of overall reaction rate constant (kov) and second-order reaction rate constant (k2,MPDL), from the experimental absorption data. Additionally, the physical properties and mass transfer data (i.e., density, viscosity, Henry’s constant, and liquid phase mass transfer coefficient) of aqueous MPDL solutions were experimentally measured and comprehensively discussed. In the present work, the experimental k2,MPDL is firstly introduced and can be expressed as: k2,MPDL=1.66×107Exp-3903.6T. The results also show that the CO2 absorption kinetics of MPDL can be ranked as: MEA > DEA > AMP > MPDL > MDEA. Even though novel MPDL has faster kinetics than conventional MDEA, it possesses too slow absorption kinetics to be used as a single solvent. Thus, it should be promoted with a very reactive amine to improve the overall CO2 absorption performance.

Macroscale modeling the methanol anomalous transport in the porous pellet using the time-fractional diffusion and fractional Brownian motion: A model comparison

In this paper, we present physically-based macroscale models for the simulation of the mass transport process through the solid porous media. The models are based on the standard diffusion, time-fractional diffusion, and the fractional Brownian motion diffusion equations respectively. For the experimental verification of the developed models, the transport process in zeolite ZSM-5 pellet was studied using the methanol as a probing agent. Treating the experimental data by the second Fick's law of diffusion demonstrated no correspondence between the methanol transport and the Fickian concept. Therefore, the models, based on the time-fractional diffusion and the fractional Brownian motion, were adopted for a description of the experimental mass transfer kinetic. Both models provided an excellent correspondence between the experimental data and the relevant asymptotic solutions. For the time-fractional diffusion model, the asymptotic analysis of the experimental data revealed the equivalence of the anomalous diffusion exponents measured at the short and the long times. In contrast, the anomalous diffusion exponents estimated in the frame of the fractional Brownian motion model are different for the short and the long times. These findings allowed us to speculate on the applicability of the certain anomalous diffusion model in the experimental scenario studied. The obtained conclusions are additionally supported by an analysis of the mass transfer data presented in the literature.

Mass transfer during bubble-free polymer devolatilization: a systematic study of surface renewal and mixing effects

This paper deals with a systematic study of bubble-free polymer devolatilization. Experimental degassing tests are combined with a surface renewal analysis. For this purpose, a simplified extruder model is used as representative rotating degassing machine. It is a partially filled agitator vessel with a blade stirrer. A model substance system consisting of highly viscous polydimethylsiloxane as polymer and 1,1,2-trichloro-1,2,2-trifluoroethane as volatile allows the experiments to be carried out at ambient temperature. The driving force for the mass transfer is achieved by reducing the partial pressure in the gas phase via an inert gas flow of nitrogen. This allows the specific investigation of the mechanism of film degassing. The temporal decrease in the concentration of volatiles in the polymer solution is measured thermogravimetrically at three different filling levels and three different rotational speeds in a total of 18 test series. At the same time, the free surfaces and renewal times are determined by video recordings and numerical simulations. For this, the free CFD software OpenFOAM is used with a VOF-based free surface solver. The numerical results are validated by the experiments. It is shown that the deviations of the measured mass transfer data from the theoretical predictions of the common surface renewal models depend on the degassing degree. Mixing is the decisive factor which can be taken into account in the form of a corrected model for the design of degassing machines. Furthermore, it is shown that the gas-side mass transfer resistance is not negligibly small in all cases.

Nonthermal pretreatments enhances drying kinetics and quality properties of dried ginger (Zingiber officinale Roscoe) slices

AbstractThe objective of this present work was to investigate the effect of ultrasound (US), osmotic dehydration (OD), and osmosonication (OS) pretreatment on microstructure, weight loss, texture, mass transfer, chromatic properties and drying kinetics of ginger slices under relative humidity convective drying. The results revealed that OS pretreatment yielded higher weight loss (16.5%) and lower firmness (12.11 N) than US (9.8%, 20.33 N) and OD (6.5%, 15.30 N). Microstructure analysis showed that OS, US, and OD pretreatments altered cell structure and resulted in the observable formation of several microchannels and collapsed the cell structure. Mass transfer data showed that the OS pretreated sample led to higher solid gain (3.2%) and water loss (5.1%) than the US (2.36%, 4.2%) and OD (1.7%, 2.53%) pretreatments. The chromatic property analysis revealed that the chroma value and hue angle was higher for OS treated sample (29.74, 88.77°) compared the US (26.95, 85.76°) and OD (22.96, 82.24°) treated sample. Among the three pretreatments, OS was found to enhance the drying kinetics comparative to the US and OD pretreated sample. Weibull model fitted well to the experimental results (R2 > .99) than the first order.Practical applicationsUltrasound, osmotic dehydration, and osmosonication are unique pretreatment techniques that are widely used prior to drying of various agricultural products due to its numerous advantages over conventional methods. Its application in the drying of foods could help shorten the drying time, reduce processing costs, improve energy consumption and efficiency and preserve the physical and nutritional properties of the dried product. The outcomes of the present study will provide a better understanding of different nonthermal pretreatment methods and also make available more information for selecting pretreatment techniques for ginger drying.

Enhancing biodegradation of toxic industrial wastewaters in a continuous two-phase partitioning bioreactor operated with effluent recycle

In this study, we propose the application of a Continuous Two-Phase Partitioning Bioreactor (C-TPPB) operated with the tubing effluent recycle to enhance the biodegradation of toxic substrates in industrial wastewaters under severe loading conditions. Stepwise increasing influent concentrations (from 200 to 900 mg L−1) of 2,4-dichlorophenol (2,4-DCP) were fed to a C-TPPB operated with Hytrel G3548 tubing to simulate phenolic wastewater. Practically complete 2,4-DCP removal has been achieved during the entire experimental period, but the increased load reduced biodegradation efficiency. At influent concentration of 700 mg L−1, the first effluent recycle (recycle /influent flow rate ratio = 0.3) was applied: biodegradation efficiency doubled from 40 to 80% and was maintained until influent concentrations of 800 mg L−1. Higher influent concentrations caused a decrease in 2,4-DCP biodegradation, so the effluent recycle ratio was increased to 0.5 at 900 mg L−1 and, also in this case, the bioreactor showed a fast recovery (∼ 24 h) of the biodegradation efficiency at 80%. Mass transfer data analysis showed that the effluent recycle resulted in an increase of the mass transfer coefficient. This positive effect, joined with the reduction of the influent concentrations, demonstrated the feasibility of recycle application in enhancing the C-TPPB performance.

Absorption and desorption mass transfer rates as a function of pressure and mixing in a simple hydrocarbon system

Determining the time required for degassing within a gas–liquid separator is usually accomplished by assuming thermodynamic equilibrium between the two phases and calculating the time required for entrained gas bubbles to rise out of the liquid. However, if the gas–liquid separation is being performed at elevated pressures, the inlet multiphase fluid may not be at thermodynamic equilibrium, thus the chance for solution gas to evolve out of the liquid must also be accounted for. There is, however, a paucity of mass transfer data in hydrocarbon systems available at elevated pressures. For the current experimental study, the rates of absorption and desorption of methane in a n-dodecane solution were measured in a batch stirred tank system at pressures ranging from 3.45 to 10.34 MPa and mixing speeds ranging from 100 to 250 rpm. All absorption and desorption experiments were performed using the same physical and hydrodynamic conditions. Additionally, care was taken in ensuring that the gas–liquid interface during mass transfer remained flat, allowing for the explicit calculation of the liquid-side mass transfer coefficient. Within the experimental variability, the rates of absorption and desorption were found to be the same in most cases. The mixing speed was found to be the main variable affecting the rate of mass transfer, while the saturation pressure was found to have little effect. The process was well described by the theoretically derived solid surface eddy cell model presented by Lamont and Scott, resulting in an average absolute error of 12.3% between the predicted and measured mass transfer coefficients.

Turbulent Flow with the Inner Cylinder Rotating

The dissipation theorem does a respectable job of describing turbulent mass transfer in the rotating-cylinder system, although parameters still need to be obtained by fitting against experimental data. Unfortunately the available experimental data show discrepancies that hamper theoretical development. This is part of a long-range program to compare the predictions of the dissipation theorem to systems ranging from pipe flow and rotating cylinders to developing flows on a rotating disk and on a flat plate at zero incidence, where extensive experimental data exist. One learns that values of the eddy viscosity should superpose after dividing by the stress parameter R+ in order to obtain coherent behavior at very large Reynolds numbers. One innovation here is to use the mass-transfer data as a proxy for the absence of torque data. One finds that the data of Eisenberg and of Mohr do not constitute a single coherent data set even though they were obtained on the same apparatus and with the same chemical system. New experimental data are needed to resolve these discrepancies. The dissipation theorem is supposed to enhance our understanding of turbulence and permit prediction of the behavior of turbulence in a variety of systems. The next step is to apply it to developing flows on a flat plate and a rotating disk.

Recovery of copper from spent catalyst using acid leaching followed by electrodeposition on square rotating cylinder

In this study, the kinetics of acid leaching of a spent catalyst containing CuO was investigated. The effect of key parameters such as type of acid (H2SO4, HCl, Oxalic acid), concentration of acid (0.5–2 M), stirring speed (200–600 rpm), liquid to solid ratio (40–200 ml/g) and temperature (27–55 °C) on the rate of leaching was determined experimentally. The treatment of present leaching data using shrinking core model (SCM) revealed that diffusion through the catalyst's ash layer is the rate controlling step. Activation energy values confirmed also the diffusion controlled nature of the leaching process. Kinetics of copper recovery from synthetic leach liquor by electrochemical deposition on square rotating cylinder was studied under different conditions using limiting current technique measurements. The rate of copper electrodeposition was expressed by the mass transfer coefficient. The present results showed that mass transfer coefficient increases with decreasing initial concentration of copper ions and increasing rpm. The present mass transfer data for copper deposition under constant current electrolysis at square rotating cylinder was correlated by the following dimensionless equation: Sh = 0.4557 Sc0.33 Re0.59 for the conditions 657 < Re < 2373, 2165.21 < Sc < 2819.2.

Falling film evaporation of aqueous lithium bromide solution at low pressure

Horizontal tube bundles are often used as falling film evaporators in absorption chillers, especially for systems working at low pressure with H2O/LiBr. The heat and mass transfer processes in these apparatuses are affected by several physical effects and the geometrical design of the heat exchanger, for example the material properties of the working fluid or the surface structure of the heat exchanger. Several influencing parameters are summarized and evaluated. Correlations for the prediction of the heat transfer coefficients of falling film evaporators from the literature are discussed concerning their applicability in dependence of the working conditions of the evaporator in an absorption chiller. In this work, experimental investigations are carried out in a falling film evaporator consisting of a horizontal tube bundle with eighty horizontal tubes installed in an absorption chiller because of a lack of consistent data for heat and mass transfer in the literature. The heat and mass transfer mechanisms and the flow pattern in the falling film are analysed and compared with correlations from literature. The deviations of the experimental data from those of the correlations are within a tolerance of 30%. These deviations may be explained by a change of the flow pattern at a lower Reynolds number than compared to the literature.

Liquid – Solid mass transfer behaviour of heterogeneous reactor made of a rotating tubular packed bed of spheres

The mass transfer behaviour of a rotating tubular packed bed of spheres was studied using an electrochemical technique which involved measuring the limiting current of the cathodic reduction of potassium ferricyanide in a large excess of supporting electrolyte. Variables studied were bed rotation speed, physical properties of the solution, and bed thickness (L). The mass transfer coefficient was found to increase with increasing bed rotation speed and decreases with increasing bed thickness. The mass transfer data were correlated by the equation:Sh=0.126Sc0.33Re0.52LdP-0.8Importance of the present study in the design and operation of high space – time yield heterogeneous reactors such as electrochemical reactors, catalytic reactors, photocatalytic reactors and immobilized enzyme biochemical reactors suitable for conducting diffusion controlled liquid – solid reactions was highlighted. Advantages of the present reactor in conducting small scale production compared to other reactors were pointed out.