Effective Interfacial Area Research Articles

Liquid film flow and area generation in structured packed columns

Several correlations are available in the literature for the prediction of wetted area or the effective interfacial area in packed columns. A careful examination shows considerable discrepancies in the calculated areas and conflicting predictions concerning the influence of viscosity on the interfacial areas. In this work, the effect of physical properties of liquids and of surface treatment on wetted area of structured packings was experimentally studied. Several wetting tests were performed on metallic and ceramic plates with flat, smooth or textured surfaces, using a circulation system, specially designed for this purpose. The liquid film width and thickness were measured for solutions with different surface tension and viscosities in a wide range (1 to 200 cP). The experimental results show that the liquid film width, and hence the wetted area, decreased with liquid viscosity, contrary to earlier correlations in the literature. Also the influence of contact angle is not so strong as stated in the literature for random packings. In this study, a new statistical correlation for the estimation of the wetted area and for the liquid film thickness is proposed, reflecting the measured variations with viscosity and advancing contact angles.

Mass transfer parameter estimation using optimization technique: Case study in CO2 absorption with chemical reaction

AbstractThis paper proposes a new approach of applying an optimization technique to simultaneously determine a physical liquid—film mass transfer coefficient (KoL) and effective interfacial area (av) from a pilot plant data. The mass transfer mechanism of the CO2‐NaOH system was modeled using the two‐film theory to represent the behaviors of packed absorbers. The model presents an overall absorption rate (Rv) as a function of KoL and av. The optimization algorithm used in this study follows a modified Levenberg‐Marquardt method with a trust region approach. The Rv predictions from the model are in good agreement with the experimental data, with an average error of 6.5%.

Magnetic Resonance Imaging Study of the Dissolution Kinetics of Octanol in Porous Media

Magnetic resonance imaging (MRI) is used to visualize the dissolution of entrapped ganglia or “blobs” of octanol within the pore space of a randomly packed bed of glass ballotini, by a mobile aqueous phase. MRI provides three dimensional images, able to distinguish the solid, hydrocarbon, and aqueous phases, as well as velocity maps of the mobile aqueous phase. Dissolution of the hydrocarbon phase has been modeled using a one dimensional advection–dispersion description incorporating a mass transfer term between the hydrocarbon and aqueous phases. Essential to this mass transfer term is a description of the interfacial area between the hydrocarbon and aqueous phases which is actively involved in dissolution and which can be determined directly from the images. The experimental data are best modeled by evaluating an effective interfacial area term characterizing the hydrocarbon/water boundary which excludes the narrowest constrictions within the interparticle space. MRI visualizations of the structure of the pore space and the flow processes occurring within it, demonstrate that heterogeneities in the flow at the length-scale of individual pores within the interparticle space cause significant heterogeneity in the dissolution process which becomes significant at low hydrocarbon saturations.

Total Reflux Simulation of Packed Column Distillation.

This paper presents a simulation algorithm with a rate-based model for a packed distillation column at total reflux.The proposed algorithm consists of 1) composition and temperature profile calculation, which is slightly modified from the one for steady-state continuous distillation at finite reflux, and 2) composition correction for accelerating convergence with the overall θ method based on the component material balance considering liquid hold-up within the distillation column.Simulation results are compared with the experimental results of a ternary system obtained from a 0.21 m diameter packed distillation column. Fairly good agreement is obtained, though proper evaluation of the effective interfacial area and liquid hold-up distribution is essential for better simulation.

Field Evaluation of Interfacial and Partitioning Tracers for Characterization of Effective NAPL‐Water Contact Areas

AbstractThe use of surface‐active tracers for measuring the interfacial area between no aqueous phase liquids (NAPLs) and water was evaluated in a hydraulically isolated test cell installed in a surficial aquifer located at Hill Air Force Base (AFB), Utah. Interfacial tracers were developed at the University of Florida for quantifying immiscible fluid‐fluid interfaces (air‐water or NAPL‐water) in porous media. Sodium dodecyl benzene sulfonate (SDBS) was used as the interfacial tracer to measure the effective NAPL‐water interfacial area (aNw), while 2,2‐dimethyl‐3‐pentanol (DMP) was used as the partitioning tracer to estimate the NAPL saturation (SN). The observed retardation of SDBS and DMP when compared to a nonreactive tracer (bromide or methanol) at eight multilevel sampling locations and one extraction well, was used to quantify the aNw and SN values averaged over the interval between the injection wells and each monitoring point. The NAPL morphology index, defined here as HN= aNw/φSN (φ= porosity), varied significantly within the test cell. In locations where the magnitude of HN was large, the NAPL was assumed to be more or less uniformly spread, providing good contact with the mobile fluid. In contrast, regions with low HN values were assumed to have NAPL that was more heterogeneously distributed as isolated patches providing poor contact with the mobile fluid. The index HN, provided by the combined use of interfacial and partitioning tracers, has important implications for NAPL source region remediation employing in situ flushing technologies.

Properties of La 0.6Sr 0.4Co 0.2Fe 0.8O 3− x (LSCF) double layer cathodes on gadolinium-doped cerium oxide (CGO) electrolytes : II. Role of oxygen exchange and diffusion

The area specific resistivity (ASR) of La 0.6Sr 0.4Co 0.2Fe 0.8O 3− x cathodes on Gd-doped ceria electrolytes has been measured over the temperature range 325–725°C. The ASR values for single layer porous cathodes could be satisfactorily interpreted in terms of available data for oxygen surface exchange coefficients. By introducing a thin (∼1 μm) dense layer of La 0.6Sr 0.4Co 0.2Fe 0.8O 3− x (LSCF) adjacent to the gadolinium-doped cerium oxide (CGO) electrolyte the resistivity values were decreased by a factor of 2–3 times, which could be explained by increasing the effective interfacial contact area between the LSCF and GGO. However calculations using data for oxygen self diffusion coefficients indicated much higher ASR values than determined experimentally for these duplex layer cathode structures. It is necessary, therefore, to invoke enhanced oxygen ion transport through the dense layer which could arise either due to the development of A-site deficient LSCF material, or too rapid diffusion via grain boundaries.

Analysis of packed distillation columns with a rate-based model

Multicomponent packed column distillation is simulated using a rate-based model and the simulation results are compared with the experimental results obtained from a 0.2 m diameter pilot-scale packed column. The simulation algorithm used is previously proposed by the authors, which based on an equation-tearing method for (6c+7) equations of one packing segment and the whole column is solved by an iterative segmentwise calculation with the overall normalized θ method for acceleration. The performance of two packings is examined by simulating the pilot-scale column experiments using the published correlations for estimating liquid and vapor phase mass transfer coefficients and an effective interfacial area.

Microstructural evolution during solidification of austenitic stainless steel weld metals: A color metallographic and electron microprobe analysis study

Structural evolution during solidification of austenitic stainless steel welds plays a crucial role in solidification cracking and microsegregation. Currently, there is no unambiguous method available to study the solidification mechanism in detail. The present investigation was undertaken to explore the potential of color metallography for revealing solidification structures. Weld composition was altered by adding varying amounts of nitrogen such that its location with respect to the phase diagram is moved in a specified direction. The controlled variations in the solidification mechanism thus brought about were studied metallographically, using Beraha's etchant and electron microprobe analysis. Metallographic studies complemented by electron probe microanalysis demonstrated color metallography to be a highly useful, simple, and reliable technique for revealing solidification structures. Color etching enables the quantitative estimation of high-temperature phases in the ferritic-austenitic mode of solidification. It also reveals the three-phase reaction mechanism in the (L+δ+γ) region in detail. In fully austenitic structures, color etching reveals the growth patterns of cell structures and the effective interface area where impurities are expected to segregate.

Effective interfacial area in magnetically stabilized slurry bubble column

The influence of magnetic field on effective interfacial area in a slurry bubble column of magnetizable particles (magnetic) has been studied by using the theory of absorption accompanied by chemical reaction. The model system used was oxidation of sodium sulphite in presence of cobalt sulphate as catalyst. The effective interfacial area increaseswith the increase in intensity of magnetic field. The increase was approximately 1.4 times ( a H a H=0 =1.4 ) for a field strength of 462 Oersteds with 2% magnetite concentration.

Distillation Columns Containing Structured Packings: A Comprehensive Model for Their Performance. 2. Mass-Transfer Model

This is the second part of a two-part paper dealing with the fluid mechanics and mass transfer in structured packings for distillation column service. The first part elucidated pressure drop, flooding, and liquid holdup. The second part covers the generation of effective interfacial area and provides a general correlation for predicting the mass-transfer efficiency as a function of surface type, packing geometry, phase flow conditions, and fluid properties. The mass-transfer model has been tested against a variety of commercial structured packings, for distillation pressures ranging from 0.33 to 20.4 bar. In all cases the fit of the data is excellent, with the possible exception of the highest pressures, where additional factors of axial mixing appear to have an effect.

Effect of Artificially Provoked Marangoni Convection at a Gas/Liquid Interface on Absorption

The effect of artificially provoked Marangoni convection on absorption of CO2 by water was theoretically and experimentally investigated. The effectiveness of absorption enhancement by continuously dissolving aqueous binary mixtures of methanol, ethanol, and n-propanol at a water surface was studied. Although the mass-transfer coefficient values were underpredicted, the theoretical predictions were found to be qualitatively verified by the experimental results. The discrepancy was attributed to the inability of the theory to consider the effective interfacial area for the absorption process in the presence of induced turbulence. A dimensionless equation for correlating the experimental mass-transfer coefficient in the presence of interfacial turbulence was satisfactorily developed.

Electronic conductivity and current instability in superionic crystals

The current-voltage characteristics of −Ag¦RbAg 4I 5¦C + cell are measured and described in terms of a model assuming that the electron current across the electrochemical cell is essentially defined by the transfer of electrons through the interface. The position of the Fermi level in the band gap and the value of the electronic conductivity σ e ∼- 2.5 × 10 −9 Ω −1 cm −1 are determined. The role of the near contact region and silver dendritic clusters in the process of electron transport in RbAg 4I 5 superionic crystals are studied. The onset of the exponential rise of the current at increasing voltage V (at V ⩾ 450 mV) is described within the model based on the conception that the silver dendritic clusters fractally grow at the interface. It is shown that the increase of the voltage leads to growth of the effective interface area (due to the cluster structure formation) and as a result to the exponential increase of the current through the cell at V ⩾ 450 mV. At constant voltage on the cell we observed experimentally the electronic current instability. We suppose that at this voltage some of the clusters reach the opposite electrode that leads to stochastic current oscillations. The number of these clusters increases with the voltage growth and therefore the current oscillations become more frequent. All experimental data are well described within the framework of the theory of reversible diffusion limited aggregation without branching.

A study on characteristics of a modern structured packing

The hydraulic characteristics including dry pressure drops, liquid holdups, flooding data, effective interfacial areas, and wet pressure drops of a modern structured packing (Sulzer BX) were studied using the air-water system. As a result, a predictive equation for the wet pressure drops of this structured packing at below the flooding point was derived for the design of the distillation column. The equation was tested with the experimental data obtained from the practical vacuum distillations. It was suggested that the equation is useful for the vacuum distillation under the flooding point, but the deviation is increased above the flooding point.

Mass transfer in packed columns: The cylinder model

AbstractIn order to predict mass transfer in packed columns, it is necessary to know the interfacial area. The well‐known and often cited equation (Onda, Kolev, Zech, etc.) do not yield precise values for the mass transfer coefficient βL ae or the interfacial area ae, especially for modern packing elements. A new model will be presented which takes into account the structure of packing (cylinder model) as well as the structure of the liquid hold‐up. This model allows the separation of liquid flow through packings into its main constituents, i.e. rivulets and drops (freely falling). The determination of the structure of liquid flow allows the prediction of effective interfacial areas as well as of volumetric mass transfer coefficients for irrigated large packing elements manufactured from plastics, metals or ceramic. The applicability to novel future packings is one of the advantages of the new model.

Optimal electrolytic chloriding of silver ink electrodes for use in electrical impedance tomography.

The electrode-electrolyte interface impedance may be simplistically modelled by an equivalent circuit comprising a resistance, RTOTAL, in series with an empirical, constant phase angle impedance, ZCPA. This pseudo-capacitance can be thought of as representing empirically the non-faradaic, double layer capacitance in the presence of specific adsorption and surface roughness effects. RTOTAL is the sum of the lead and electrolyte resistances. Depositing a thin layer of silver chloride on silver electrodes can yield improved electrical performance characteristics (potential and impedance) when used in conjunction with a chloride gel. An electrolytically deposited AgCl layer tends to have a rough surface profile thus leading to an increase in the effective interface area. This gives rise to a decrease in RTOTAL and ZCPA, both of which are desirable. Unfortunately AgCl is a relatively poor conductor. Increasing layer thickness causes RTOTAL to increase, thus adversely affecting the inter-electrode impedance at high frequencies. Electrode systems for use in electrical impedance tomography therefore require only relatively thin layers of AgCl.

Influence of effective interfacial areas in the operation and control of packed distillation columns

The different types of packings commonly used in distillation columns possess different wetting characteristics due to their shape and the nature of their surfaces. The way interfacial area is created, renewed, and maintained in these different geometries has a marked effect on the efficiency of the packings, as well as on the response of the column to different operating conditions. We explore the effect of the interfacial area behavior of different packings on the way distillation column responds to varying loads. Implications for the design of control strategies are discussed as well. Experimental data obtained previously were used to establish the basis for the analysis

Computer Simulation of Microstructural Evolution in Thermomechanical Processing of Steel Plates.

The computer simulation model of microstructural evolution on the basis of chemical thermodynamics and classical nucleation and growth theory has been developed. The metallurgical phenomena in thermomechanical treatment of steel, such as austenite grain growth, recrystallization and growth, carbonitride precipitation and austenite to ferrite phase transformation can be predicted by the model. The influences of steel chemistry and thermomechanical condition on the transformed microstructure of 0.10C-1.5Mn-0.35Nb steel (high C-high Mn steel) and 0.06C-1.25Mn-0.035Nb steel (low C-low Mn steel) are evaluated by computer simulation. With the increase of C and/or Mn concentrations, the volume fraction of second phase increases and the ferrite grain size is refined C-high Mn steel, the transformed microstructure consists of ferrite and pearlite phases at lower cooling rates and/or larger effective austenite interfacial area per unit volume, SV. The volume fraction of second phase increases with the increase of cooling rate and/or the decrease of SV value. The second phase of the steel at higher cooling rates is bainite. The transformed microstructure of low C-low Mn steel consists of ferrite and bainite phases. The influences of the rolling condition and the cooling rate on the transformed microstructure are smaller in low C-low Mn steel. However, the transformed microstructures is apparently influenced by the start temperature of accelerated cooling.

Investigations of the Electrical Properties of Porous Silicon

We report capacitance and current‐voltage measurements of porous silicon in contact with sputter‐deposited aluminum. Three different substrates: 30–50 Ω‐cm boron‐doped (p−‐type), 0.01–0.03 Ω‐cm boron‐doped (p+‐type), and 0.003–0.005 Ω‐cm phosphorus‐doped (n+‐type) silicon, are used as starting material. Porous silicon formed from p−‐ and p+‐type substrates exhibits full‐ and partial‐carrier depletion, respectively. The electric field, potential distribution, and capacitance for full depletion are derived and shown to compare qualitatively with measured capacitance as a function of porous layer thickness for p−‐type porous silicon. Impedance variation with porous layer thickness was used to determine the resistivity of p−‐type porous silicon as . A three‐dimensional space‐charge region accounting for the observed partial depletion in p+‐type porous silicon is described in detail. Capacitance with bias was used to measure the effective interface area of p+‐type porous silicon. This reduced interface area can be explained in terms of a lateral depletion region surrounding each pore, with an average of 0.8 times the pore radius. Current‐voltage measurements indicate a blocking contact between sputtered aluminum and both p−‐ and p+‐type porous silicon, in contrast to ohmic contacts between sputtered aluminum and nonporous p−‐ and p+‐type silicon. Capacitance‐ and current‐voltage dependences of n+‐type silicon indicate that in this material conversion to porous silicon has a relatively small effect.

Effective interfacial area in gas-liquid cocurrent downflow through packed beds

The effective interfacial area in cocurrent gas-liquid downflow through packed beds is analysed taking into consideration the specific surface of the packing and the inter-dispersion of the phases. Predictive equations valid for low and high interaction regimes are developed based on the experimental data of the present study, and are satisfactorily compared with the data of the earlier investigations.

Effect of bile salts on monolayer curvature of a phosphatidylethanolamine/water model membrane system

A partial phase diagram of the ternary system dioleoylphosphatidylethanolamine (DOPE)/sodium cholate/water has been determined using 31P Nuclear Magnetic Resonance (NMR) spectroscopy. In the absence of cholate, it is well known that the DOPE/water system forms a reversed hexagonal (HII) phase. We have found that addition of even small amounts of cholate to the DOPE/water system leads to a transition to a lamellar (L alpha) phase. At higher cholate concentrations, a cubic (I) phase (low water content) or a micellar solution (L1) phase (high water content) is present. Thus, cholate molecules have a strong tendency to alter the lipid monolayer curvature. Increasing the concentration of cholate changes the curvature of DOPE from negative (HII phase), through zero (L alpha phase), and finally to a phase of positive curvature (micellar solution). This observation can be rationalized in terms of the molecular structure of cholate, which is amphipathic and has one hydrophobic and one hydrophilic side of the steroid ring system. The cholate molecules have a tendency to lie flat on the lipid aggregate surface, thereby increasing the effective interfacial area of the polar head groups, and altering the curvature free energy of the system.