Showing papers on "Mass transfer coefficient published in 2002"
TL;DR: Activated carbon derived from bagasse, an agricultural waste material, has been investigated as a replacement for the current expensive methods of removing heavy metals from wastewater and it was concluded that the adsorption occurs through a film diffusion mechanism at low as well as at higher concentrations.
1,122 citations
TL;DR: In this paper, the authors present a packed-bed approach for the use of porous silicon as a catalyst support, in the form of a thin layer covering microstructured channels, to enhance mass transfer relative to an open channel.
Abstract: Using silicon microfabrication technology, microchemical devices have been constructed for the purpose of conducting heterogeneously catalyzed multiphase reactions. The motivation behind the design, the fabrication approach, and the experimental characterization are presented for two classes of devices. The first design involves multiple parallel channels with integrated filter structures to incorporate standard catalytic materials. These catalysts are in the form of finely divided porous particles in a packed-bed arrangement. The second device involves the incorporation of porous silicon as a catalyst support, in the form of a thin layer covering microstructured channels. These microstructured channels simulate the structure of a packed bed and enhance mass transfer relative to an open channel. The ability to incorporate features at the tens-of-microns scale can reduce the mass-transfer limitations by promoting mixing and dispersion for the multiple phases. Directly integrating the catalyst support structures into the channels of the microreactor allows the precise definition of the bed properties, including the support's size, shape and arrangement, and the void fraction. Such a design would find broad applicability in enhancing the transport and active surface area for sensing, chemical, and biochemical conversion devices. Reaction rates for the gas-liquid-solid hydrogenation of cyclohexene using the integrated catalyst with porous silicon as a support compare favorably to those rates obtained with the packed-bed approach. In both cases, the mass transfer coefficient is at least 100 times better than conventional laboratory reactors.
235 citations
TL;DR: Its very high sorption capacity and relatively low production cost make chitosan an attractive sorbent for the removal of heavy metals from waste streams.
215 citations
TL;DR: In this article, a zero-order kinetics for both non-catalytic and catalytic oxalic acid ozonation was investigated in an agitated slurry semibatch reactor where powdered TiO2 has been used as a catalyst.
Abstract: The ozonation of oxalic acid has been carried out in an agitated slurry semibatch reactor where powdered TiO2 has been used as a catalyst. The presence of TiO2 catalyst significantly improved the ozonation rate of oxalic acid compared to the results from non-catalytic ozonation. For gas flow rates higher than 12 l h−1 and agitation speed above 100 rpm, the catalytic process rate was chemically controlled. The kinetic study led to a zero-order kinetics for both the non-catalytic and catalytic ozonations. These experimental findings were corroborated by a mechanism of reactions. This kinetics also supported experimental results at different temperatures, ozone partial pressure and mass of catalyst per slurry volume. At low gas flow rate, where both mass transfer and chemical reaction controlled the process rate, the external gas to liquid mass transfer coefficient was also determined.
210 citations
Journal Article•
TL;DR: In this article, a numerical and an analytical model were developed to predict the volatile organic compound (VOC) emission rate from dry building materials, and the predictions of the models were validated at two levels: with experimental results from the specially designed test and with predictions made by a CFD model.
165 citations
TL;DR: In this article, a large draft-tube air-lifted bioreactor with Prochem hydrofoil impellers placed in the draft tube was analyzed for gas holdup, mixing, liquid circulation and gas-liquid oxygen transfer.
165 citations
TL;DR: In this article, a numerical and an analytical model were developed to predict the volatile organic compound (VOC) emission rate from dry building materials, and the predictions of the models were validated at two levels: with experimental results from the specially designed test and with predictions made by a CFD model.
161 citations
TL;DR: It was confirmed that the range of CO2 concentration used in the experiments was cost-effective for mass culture and the overall volumetric mass transfer coefficient, kLa, was evaluated for several different flat-plate sizes.
Abstract: To optimize the aeration conditions for microalgal biomass production in a vertical flat-plate photobioreactor (VFPP), the effect of the aeration rate on biomass productivity was investigated under given conditions. Air enriched with 5% or 10% (v/v) CO2 was supplied for the investigation at rates of 0.025–1 vvm. The CO2 utilization efficiency, change of pH in the medium, and the optimum aeration rate were determined by evaluating biomass productivity. To investigate the VFPP mass transfer characteristics, the overall volumetric mass transfer coefficient, k
La, was evaluated for several different flat-plate sizes. Increasing the height of the VFPP could improve both the mass transfer of CO2 and the illumination conditions, so this appeared to be a good method for scaling up. Based on a comparison of the k
La value at the optimum aeration rate with previously reported results, it was confirmed that the range of CO2 concentration used in the experiments was cost-effective for mass culture.
133 citations
TL;DR: In this article, the fixed bed extraction of black pepper essential oil using supercritical carbon dioxide was modeled by the extended Lack's plug flow model developed by Sovova (Sovova's model).
116 citations
Book•
21 Mar 2002TL;DR: In this article, an energy transfer model is proposed to describe the energy conservation properties of a mass transfer with respect to temperature, mass conservation, and kinetic properties of the mass transfer.
Abstract: Contents ENERGY TRANSFER Equilibrium, Energy Conservation, and Temperature Modes of Heat Transfer Governing Equation and Boundary Conditions of Heat Transfer Conduction Heat Transfer: Steady-State Conduction Heat Transfer: Unsteady-State Convection Heat Transfer Heat Transfer with Change of Phase Radiative Energy Transfer MASS TRANSFER Equilibrium, Mass Conservation, and Kinetics Modes of Mass Transfer Governing Equations and Boundary Conditions of Mass Transfer Diffusion Mass Transfer: Steady-State Diffusion Mass Transfer: Unsteady-State Convection-Dispersion and Convection-Diffusion Mass Transfer APPENDIX Summary of Processes and Equations Physical Constants, Unit Conversions, and Mathematical Functions Heat Transfer and Related Properties Mass Transfer Properties Miscellaneous Environmental Data Equations of Motion in Various Coordinate Systems Some Useful Mathematical Background Index
113 citations
TL;DR: In this article, a kinetic model for the photocatalytic degradation of formic acid in an immobilized system is presented, including the dependency of the reaction rate on the concentration of Formic acid and oxygen, the catalyst layer thickness and the light flux.
TL;DR: In this article, a volume-of-fluid (VOF)-based numerical method for calculating heat transfer or mass transfer of a species within and between fluids with deforming interfaces is described.
Abstract: A new volume-of-fluid (VOF)-based numerical method for calculating heat transfer or mass transfer of a species within and between fluids with deforming interfaces is described. The algorithm is tested first against an analytical solution for diffusion from a sphere, and good agreement between theory and calculation is shown. The method is then demonstrated by predicting (a) heat transfer from a rising bubble when the bubble forms a toroidal shape, and (b) mass transfer from a rising drop when the drop phase controls diffusion. The method is shown to be a viable approach for complex interfacial heat/mass transfer.
TL;DR: In this paper, the authors describe the mass transfer and hydrodynamics within an ear-horizontal tubular photobioreactor and determine the minimum mass transfer coefficients for O2 stripping and CO2 dissolution which would be required to achieve a desired biomass productivity.
Abstract: In photobioreactors, which are usually operated under light limitation,sufficient dissolved inorganic carbon must be provided to avoid carbonlimitation. Efficient mass transfer of CO2 into the culture mediumisdesirable since undissolved CO2 is lost by outgassing. Mass transferof O2 out of the system is also an important consideration, due tothe need to remove photosynthetically-derived O2 before it reachesinhibitory concentrations. Hydrodynamics (mixing characteristics) are afunctionof reactor geometry and operating conditions (e.g. gas and liquid flow rates),and are a principal determinant of the light regime experienced by the culture.This in turn affects photosynthetic efficiency, productivity, and cellcomposition. This paper describes the mass transfer and hydrodynamics within anear-horizontal tubular photobioreactor. The volume, shape and velocity ofbubbles, gas hold-up, liquid velocity, slip velocity, axial dispersion,Reynoldsnumber, mixing time, and mass transfer coefficients were determined intapwater,seawater, and algal culture medium. Gas hold-up values resembled those ofvertical bubble columns, and the hydraulic regime could be characterized asplug-flow with medium dispersion. The maximum oxygen mass transfer coefficientis approximately 7 h−1. A regime analysisindicated that there are mass transfer limitations in this type ofphotobioreactor. A methodology is described to determine the mass transfercoefficients for O2 stripping and CO2 dissolution whichwould be required to achieve a desired biomass productivity. This procedure canassist in determining design modifications to achieve the desired mass transfercoefficient.
TL;DR: In this article, the authors examined the effectiveness of a silicone rubber membrane to separate biogas from the liquid medium in the hydrogen fermentation reactor, and showed that silicone rubber effectively reduced the biogAS partial pressure in hydrogen fermentation, and improved the hydrogen evolution rate by 10% and the hydrogen yield by 15%.
TL;DR: In this article, the authors characterized the two-phase flow hydrodynamic behavior and mass transfer in a static mixer in a horizontal pipe and compared different arrangements of elements of the static mixer.
TL;DR: Simulations showed that the nonequilibrium mass transfer process could be characterized by the exponent beta, a parameter which described the reduction of the specific area available for NAPL volatilization.
TL;DR: In this paper, the authors investigated the effect of all three parameters on the degradation rate as well as their importance on unveiling the existence of mass transfer limitations in the liquid phase under specific conditions.
Abstract: The photocatalytic degradation of a model non-volatile chlorinated aromatic compound 4-chlorobenzoic acid (4-CBA) was investigated as a function of disk angular velocity, contaminant concentration, and incident light intensity using a rotating disk photocatalytic reactor (RDPR). The study was designed to investigate the effect of all three parameters on the degradation rate as well as their importance on unveiling the existence of mass transfer limitations in the liquid phase under specific conditions. The results showed that the reaction rate increased with disk angular velocity in accordance with a saturation-type dependency. In the range of 2–6 rpm the degradation rate increased almost linearly with disk angular velocity. Above 6 rpm, however, the influence of disk angular velocity was not significant. The initial increase in the reaction rate with disk angular velocity was attributed to the longer time available per rotation resulting in higher down flow of liquid carried by the disk and to the increase in the overall mass transfer coefficient. The rates of 4-CBA acid decomposition and Cl− mineralization at 6 rpm as a function of initial 4-CBA concentration followed Langmuir–Hinshelwood kinetics. At 6 rpm, the rates of 4-CBA degradation followed a linear dependency with incident light intensity. This was attributed to the existence of low local values of incident light intensity on the illuminated disk. With respect to the effect of these three parameters on the degradation rate, the obtained results suggested the absence of significant mass transfer limitations at disk angular velocities higher than 6 rpm. The latter was verified by additional calculations of the Damkohler (Da) number based on dimensionless analysis. The Da number was found to decrease significantly with disk angular velocity and at high disk angular velocities (ω>15 rpm), Da was much lower than 0.1, even when the concentration of the contaminant in the bulk was extremely small (i.e. 1 μmol/l).
TL;DR: Alkyl phenylphosphonic acids were used for strontium removal by supported liquid membranes (SLMs) with strip dispersion in this article, which achieved an accuracy of 8 pCi/L or lower.
Abstract: We have synthesized a family of new extractants, alkyl phenylphosphonic acids, for strontium removal by supported liquid membranes (SLMs) with strip dispersion. The stability of the SLMs has been ensured by the improved SLM with strip dispersion technique. The SLMs removed radioactive Sr-90 to the target of 8 pCi/L or lower from feed solutions of 300−1000 pCi/L. Overall mass transfer coefficient data indicate that the mass transfer resistance for the membrane phase is negligible. An analysis of mass transfer resistances shows that the interfacial resistances due to extraction and stripping reactions are dominant. Stripping with HCl was nearly quantitative and more effective than that with H2SO4. The extractant was more effective than di(2-ethylhexyl) phosphoric acid.
TL;DR: In this paper, an asymmetric hollow fiber membrane module was used to remove H2S from gas streams containing 17.9-1159 ppm H2s. But, the membrane was not designed for the removal of solvents.
TL;DR: In this article, the effect of intraparticle mass transfer limitations on the performance of heat and mass transfer kinetics is addressed. And the authors show that in the case where the intraparticles diffusional resistances are significant, the system performance is markedly decreased.
TL;DR: In this article, a knife-leading-edge surrogate surface (KSS) and a WSS covered with both a Nylasorb filter, and a greased strip were used to directly measure nitrate, sulfate, and ammonium dry fluxes in Chicago between May and October 1997.
TL;DR: In this paper, the gas phase mass transfer in the empty channels and the liquid phase transfer within the catalyst-packed channels, of the crisscrossing sandwich structures of KATAPAK-S have been studied using computational fluid dynamics.
TL;DR: In this article, the effect of free and combined convection on the mass transfer was investigated by solving the governing equations using the finite element method, and it was shown that the effect depends very strongly on the flow conditions.
TL;DR: In this article, the effect of the rotation speed and the liquid submergence on global hydrodynamic and mass transfer parameters such as the critical impeller speed, the induced gas flow rate, the gas holdup, the power consumption and the volumetric gas-liquid mass transfer coefficient were investigated.
TL;DR: In this article, the influence of relevant parameters on the osmotic evaporation process, namely temperature, stirring rate and osmotics nature and concentration, is evaluated, and the water flux is expressed as a function of the Reynolds number (Re), characterising the hydrodynamic conditions, and as a functional difference, which is the driving force of the process.
TL;DR: In this article, the solubility and dissolution of oxygen as a function of temperature and concentration of sulphuric acid was investigated in aqueous acid media, and the effect of temperature (25-55 °C), gas flow rate (0.75-2.25 l/min) and acid concentration (up to 2 M) on the mass transfer coefficient k L a between gas and liquid was evaluated.
TL;DR: In this article, a two-opposed-jets contacting device (TOJCD) was used for liquid-liquid extraction of the CBW, and the experimental results clearly indicate that TOJCD provides much higher overall volumetric (capacity) mass transfer coefficients, KLa, than those of conventional extractors.
Abstract: Liquid–liquid extraction of the recommended test system, cumene–iso butyric acid–water (CBW) as a typical example of liquid–liquid extraction processes has been carried out in a new two-opposed-jets contacting device (TOJCD). The experimental results clearly indicate that TOJCD provides much higher overall volumetric (capacity) mass transfer coefficients, KLa, than those of conventional extractors. This high overall volumetric (capacity) mass transfer coefficient, KLa, indicates greater performance capability of TOJCD relative to those of conventional contactors. In addition, the effects of the upper disk speed, solution flow rate, disk diameter, and the distance between disks on the extraction efficiency have been investigated. Furthermore, the effectiveness of two-opposed jets was evaluated by employing another new non-opposed-jets contacting device.
TL;DR: In this paper, an explicit equation for the enhancement factor of a fast irreversible second-order reaction is presented, which makes it possible to determine the effective interfacial area and the liquid-phase mass-transfer coefficient of this reaction regime.
Abstract: The paper presents an explicit equation for the enhancement factor of a fast irreversible second-order reaction. The equation makes it possible to determine the effective interfacial area and the liquid-phase mass-transfer coefficient of this reaction regime. With the help of a new plot as described in this paper, the Danckwerts plot, and the method for determining the interfacial area by means of a pseudo-first-order reaction the paper discusses a novel method for characterizing the reaction regime of experimental data.
TL;DR: In this paper, the authors demonstrate that significant enhancement of gas-liquid mass transfer in bubble columns can be achieved by subjecting the liquid phase to low-frequency vibrations, in the 40-120Hz range.
TL;DR: In this article, PNP is extracted from 1-octanol into an aqueous buffered solution using membrane-supported extraction in hollow fiber liquid contactors (HFLCs) containing hydrophobic, microporous polypropylene fibers.