Showing papers on "Mass transfer coefficient published in 1997"
TL;DR: In this article, the authors measured the amount of a sample compound extracted into a 1-μL drop of n-octane suspended in a stirred aqueous solution from the tip of a microsyringe needle.
Abstract: The amount of a sample compound extracted into a 1-μL drop of n-octane suspended in a stirred aqueous solution from the tip of a microsyringe needle is measured by gas chromatography (GC) as a function of time. The observed extraction rate curve is first order and yields the overall mass transfer coefficient for the sample compound, βo. For a given compound, βo varies linearly with stirring rate. Among the four compounds malathion, 4-methylacetophenone, 4-nitrotoluene, and progesterone, at a given stirring rate, βo is linearly proportional to the diffusion coefficient of the compound (Daq). This supports the film theory of convective−diffusive mass transfer, as opposed to the penetration theory. The relative standard deviation of the GC signal for 4-methylacetophenone after a 1.00 min extraction at 1500 rpm is 1.5%, which suggests that the system exhibits excellent potential as a tool for rapid analysis by solvent extraction/GC.
531 citations
TL;DR: In this article, the influence of the capillary diameter, unit cell length and gas hold-up on measured kLa and kSa coefficients was correlated by simple correlation, which showed that in both cases the mass transport is mostly determined by the liquid slug length and velocity.
310 citations
TL;DR: Good qualitative and quantitative agreement was observed, indicating that, in the context of the model, the diffusive resistance associated with lateral diffusion is sufficient to explain the overall resistance of solute permeation through the SC.
294 citations
TL;DR: In this article, the authors explored the mass transfer mechanism for SO2 diffusion through gas filled pores by simple measurements in order to identify suitable membrane structures for use in contactors for flue gas cleaning.
245 citations
TL;DR: In this paper, a more rigorous development of the stagnant film model is presented, providing a much firmer mathematical justification for this approach as well as a more quantitative description of the limitations of this model.
229 citations
TL;DR: In this paper, a simple diffusion-reaction model was proposed to describe the measured data, and the influence of operational parameters was evaluated in order to establish ways to affect the NO 2 − concentration.
167 citations
TL;DR: In this article, the mass transfer coefficient (k) in reverse osmosis was estimated using the combined Spiegler-Kedem/film theory model and the solution-diffusion model.
163 citations
TL;DR: In this article, mass transfer through the solid boundary of a turbulent channel flow is analyzed by means of large-eddy simulation (LES) for Schmidt numbers Sc=1, 100, and 200.
Abstract: Mass transfer through the solid boundary of a turbulent channel flow is analyzed by means of large-eddy simulation (LES) for Schmidt numbers Sc=1, 100, and 200. For that purpose the subgrid stresses and fluxes are closed using the Dynamic Mixed Model proposed by Zang et al. [Phys. Fluids A 5, 3186 (1993)]. At each Schmidt number the mass transfer coefficient given by the LES is found to be in very good quantitative agreement with that measured in the experiments. At high Schmidt number this coefficient behaves like Sc−2/3, as predicted by standard theory and observed in most experiments. The main statistical characteristics of the fluctuating concentration field are analyzed in connection with the well-documented statistics of the turbulent motions. It is observed that concentration fluctuations have a significant intensity throughout the channel at Sc=1 while they are negligible out of the wall region at Sc=200. The maximum intensity of these fluctuations depends on both the Schmidt and Reynolds numbers ...
160 citations
TL;DR: A generalized equation relating the modified Peclet number to the concentration polarization occurring in the boundary layer is proposed and shown applicable to the majority of membrane separation processes like gas separations, reverse osmosis, ultrafiltration, pervaporation, and dissolved gas permeation in liquid as discussed by the authors.
148 citations
TL;DR: In this article, the authors investigated experimentally local heat transfer from condensation in the presence of non-condensable gases inside a vertical tube using a novel experimental apparatus for accurately measuring local heat fluxes, an extensive data base has been obtained for the condensation of pure steam, steam-air mixtures and steam-helium mixtures.
125 citations
TL;DR: In this article, the solution of Fick's law for unsteady state mass transfer in cylindrical configuration has been used to calculate the effective diffusion coefficients over a range of temperature (25-35 °C) and concentration (40-70 °B) of osmotic solution.
TL;DR: In this paper, the effect of membrane wetting pressure on the overall mass transfer performance of a microprous hollow fiber membrane module operated under partially wetted conditions in the laminar flow regime has been examined.
Abstract: Gas−liquid mass transfer has been studied theoretically in a microprous hollow fiber membrane module operated under partially wetted conditions in the laminar flow regime. Dissolved oxygen removal has been used as an example for the simulation study. The mathematical model developed consists of nonlinear partial differential equations and is solved using the orthogonal collocation technique. The effect of membrane wetting pressures on the overall mass transfer performances of the module has been examined. The results indicate that under partially wetted operating mode, a maximum overall mass transfer coefficient is attainable with respect to the water velocity, which is completely different from the results obtained under both wetted and nonwetted conditions where the overall mass transfer coefficient is generally increased with water velocity. The phenomena of partial wetting of the membrane may provide an explanation to the observation that the overall mass transfer coefficient is increased to a maximum...
TL;DR: In this paper, the ability of peat, lignite and activated chars made from peat and lignites to adsorb dyes and metals from wastewater and NO 2 from air was investigated.
Abstract: The ability of peat, lignite and activated chars made from peat and lignite to adsorb dyes and metals from wastewater and NO 2 from air was investigated. Equilibrium isotherms were determined to assess the maximum adsorption capacity of the adsorbents for the pollutants. Kinetic studies for the adsorption of dyes and metal ions onto the adsorbents were undertaken in agitated batch adsorbers. Mass transport models were tested to predict the concentration decay curves in batch adsorbers. The models tested were single resistance models based on the assumption of a single external mass transfer coefficient and two resistance models which included an internal diffusion coefficient and an external mass transfer coefficient. The surface phenomena which influence the extent and the rate of uptake have been studied. The equilibrium capacity data conform to Langmuir plots. A previously proposed model was used to evaluate the external single resistance mass transfer model and was successfully applied to predict the adsorption of metal ions in single component systems under batch conditions. It has been shown that the assumption of negligible intraparticle diffusion is valid and that external film diffusion is the rate limiting step in describing the adsorption processes at high sorbent loadings. The same type of result is not observed for the adsorption of coloured organic matter onto peat where the sorption processes cannot be successfully modelled by use of a single resistance model and a two resistance model incorporating internal diffusion is required. The surface phenomena which influence the extent and the rate of uptake of NO 2 have been studied. The type of chars produced and the activation processes affect the adsorption. As activation increases, micropore volume and surface area increase and the maximum capacity of the adsorbent increases. Surface area alone is not the only parameter which affects equilibrium uptake.
TL;DR: In this article, the spatial variation of eddy conductivity for Pr = 1 is interpreted in terms of the time dependency of diffusion from single sources, and support is provided for experimental studies which show that the dimensionless mass transfer coefficient varies as Sc−0.704 at large Sc.
TL;DR: In this article, the penetration theory of interfacial mass transfer was used to model flavor release from liquid emulsions, and the model was applied to predict the rates of release and partitioning properties of two volatiles, one hydrophilic (diacetyl) and the other hydrophobic (heptan-2-one), as a function of the oil volume fraction.
Abstract: The penetration theory of interfacial mass transfer was used to model flavor release from liquid emulsions. The model was used to predict the rates of release and partitioning properties of two volatiles, one hydrophilic (diacetyl) and the other hydrophobic (heptan-2-one), as a function of the oil volume fraction. In general the initial rates of release were faster for emulsions of lower oil content, whereas the equilibrium concentrations depended on the nature of the flavor compound and the volume fraction of oil in the emulsion. Experimental in vitro results suggested that the rate limiting step for flavor release was the resistance to mass transport across the emulsion-gas interface.
TL;DR: In this article, the authors evaluated the rates of mass transfer of the individual components of four synthetic dense non-aqueous phase liquid (DNAPL) mixtures into the aqueous phase.
Abstract: Parameters governing the rates of mass transfer of the individual components of four synthetic dense non-aqueous phase liquid (DNAPL) mixtures into the aqueous phase were evaluated. The DNAPL mixtures, composed of toluene and eight polynuclear aromatic hydrocarbons (PAHs), were designed to serve as models for coal tars and creosotes. The reactor employed provided a relatively stable interface between internally mixed but segregated aqueous and DNAPL phases. Two parameters, the aqueous phase concentration at equilibrium and the overall film mass transfer coefficient, were quantified by simulating aqueous concentration profiles with a mass-transfer-limited rate model using a statistical parameter search and data fitting routine. DNAPL phase activity coefficient values for the various compounds derived from equilibrium aqueous phase concentrations were typically within a factor of 2 of Raoult's law prediction of unity; refinement of fugacity ratio estimates for the solid PAHs brought the values even closer t...
TL;DR: In this article, the feasibility of using high-efficiency structured packing in CO 2 separation processes with a newly proposed solvent, 2-amino-2-methyl-1-propanol (AMP), was investigated.
TL;DR: In this article, the authors characterized the fast extraction period by evaporating 1,2-dichlorobenzene deposited on a shallow bed of nonporous, non-adsorbing glass spheres arranged in a packed bed with through circulation of supercritical carbon dioxide.
TL;DR: In this article, a mathematical model based on mass transfer in plant tissues was developed with the aim of finding a simple predictive model which was easy to use and yet had a broad application scope in the osmotic dehydration of foods.
TL;DR: In this article, a numerical study of the dynamic performance of an ad-hoc cooling system for automobile waste heat recovery is presented, where a new lumped parameter non-equilibrium model is developed and used to investigate and optimize the waste heat cooling system, which is estimated to operate in quicker cycles when compared with the time needed to reach equilibrium.
TL;DR: Local flow velocities were correlated with local mass transfer coefficients using a semi-theoretical mass transfer equation and the relationship between the Sherwood number, the Reynolds number, and the Schmidt number was found using the experimental data to find the dimensionless empirical constants.
Abstract: The relationship between local mass transfer coefficient and fluid velocity in heterogenous biofilms was investigated by combining microelectrodes and confocal scanning laser microscopy (CSLM). The biofilms were grown for up to 7 days and consisted of cell clusters separated by interstitial channels. Mass transfer coefficient depth profiles were measured at specific locations in the cell clusters and channels at average flow velocities of 2.3 and 4.0 cm/s. Liquid flow velocity profiles were measured in the same locations using a particle tracking technique. The velocity profiles showed that flow in the open channel was laminar. There was no flow at the top surface of the biofilm cell clusters but the mass transfer coefficient was 0.01 cm/s. At the same depth in a biofilm channel, the flow velocity was 0.3 cm/s and the mass transfer coefficient was 0.017 cm/s. The mass transfer coefficient profiles in the channels were not influenced by the surrounding cell clusters. Local flow velocities were correlated with local mass transfer coefficients using a semi-theoretical mass transfer equation. The relationship between the Sherwood number (Sh,) the Reynolds number (Re,) and the Schmidt number (Sc) was found using the experimental data to find the dimensionless empirical constants (n1, n2, and m) in the equation Sh = n(1) + n(2)Re(m) Sc(1/3). The values of the constants ranged from 1.45 to 2.0 for n(1), 0.22 to 0.28 for n(2), and 0.21 to 0.60 for m. These values were similar to literature values for mass transfer in porous media. The Sherwood number for the entire flow cell was 10 when the bulk flow velocity was 2.3 cm/s and 11 when the bulk flow velocity was 4.0 cm/s. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 681-688, 1997.
TL;DR: In this article, pendular rings are observed dissolving in an artificial porous medium consisting of a single layer of glass beads, given the simple geometry of the droplets, porescale mass transfer coefficients are calculated.
TL;DR: In this article, Sherwood-number relations for prediction of the mass-transfer coefficient for developing concentration boundary-layer have been obtained for laminar flow-regime from first principles The common flow-modules, namely, rectangular channel, tubular and radial crossflow are considered The relationships developed include the effect of suction through the membrane Relevant relations for estimation of mass transfer coefficient for cross-flow reverse osmosis and ultrafiltration are formulated
TL;DR: In this article, the authors examined liquid film and identified a relation that allows accurately evaluating the liquid film contribution to overall mass-transfer efficiency and showed that column packing height affects the liquid-side mass transfer coefficient at the usual industrial-scale liquid and gas flow rates.
Abstract: The effective mass-transfer efficiency in a column equipped with structured packings was investigated experimentally. The packings analyzed in the present work were Sulzer Mellapak 250Y, made of corrugated plastic or metal sheets, and Sulzer BX, made of plastic gauze. In the literature many works have been published on this topic, but they have mainly been oriented toward evaluating overall mass-transfer efficiency or the gas-side coefficient, leaving out closer examination of the liquid-side mass-transfer coefficient. The aim of the present work is to examine liquid film and to identify a relation that allows accurately evaluating the liquid film contribution to overall mass-transfer efficiency. Experimental results showed that column packing height affects the liquid-side mass-transfer coefficient at the usual industrial-scale liquid and gas flow rates. This result agrees with theoretical analysis on stable liquid rivulet flow.
TL;DR: This work investigated a control strategy using constant C w instead of constant transmembrane pressure for ultrafiltration processes and explored three different strategies for such control and evaluated the theoretical and industrial implications for single solute systems.
TL;DR: In this paper, a new mathematical model of evaporative fluid cooling with countercurrent air flow is presented, which consists of four ordinary differential equations with their boundary conditions and some associated algebraic equations.
Abstract: In this paper heat and mass transfer processes in evaporative fluid coolers are discussed. A new mathematical model of evaporative fluid cooling with countercurrent air flow is presented. The model consists of four ordinary differential equations with their boundary conditions and some associated algebraic equations. A method of adjusting the model to geometrical arrangement which is used in bare-tube heat exchangers is proposed. The study presents a comparison of the results computed using an analytical model with the experimental results of the evaporative water cooler test. A good agreement between the calculated and experimental values is achieved. The correction function of mass transfer coefficient introduced into the analytical model improves this agreement.
TL;DR: In this article, the authors applied dispersion to improve the mass transfer rate of poorly water-soluble gaseous pollutants during the biological treatment of waste gases in a stirred-tank reactor, and the enhancement of mass transfer rates was studied as a function of the pollutant solubility in water.
TL;DR: In this paper, three basic dyes were used: C.I. Basic Red 18 (or BR18), C. I Basic Red 46 (BR46), and C. Basic Yellow 28 (BY28), and the mass transfer coefficient was calculated by the external mass transfer model in an adsorbent according to Mckay et al.
Abstract: Activated clay was used to study the adsorption behavior of dyestuffs in synthetic wastewater containing dyestuffs. Three basic dyes were used: C.I. Basic Red 18 (or BR18), C.I. Basic Red 46 (BR46), and C.I. Basic Yellow 28 (BY28). Adsorption occurred almost instantaneously upon contact. The mechanism of adsorption was explained by a charge to the electrostatic attractive force described in the Langmuir adsorption isotherm. The mass transfer coefficient was also calculated by the external mass transfer model in an adsorbent according to Mckay et al. Parameters including species of basic dyes, initial concentration, temperature, size of adsorbent, and NaCl were extensively investigated.
Journal Article•
TL;DR: In this article, the effect of temperature and initial sugar syrup concentration on osmotic concentration of banana slices were studied at an initial ratio of slice slices: sugar solution as 1:4.
Abstract: The effect of temperature and initial sugar syrup concentration on osmotic concentration of banana slices were studied at an initial ratio of banana slices: sugar solution as 1:4. The water loss varied with sugar concentration as well as temperature. The mass transfer coefficient was found to increase with sugar concentration and temperature of the solution. The developed model can be used for prediction of water loss during osmotic concentration of banana slices within the range of experimental study.
TL;DR: In this paper, the effect of pressure on gas holdup and volumetric mass transfer coefficient appeared significantly in the case where the single nozzle with smaller diameter were used as gas disperser.