Showing papers on "Mass transfer coefficient published in 2006"
TL;DR: In this paper, a mathematical model was developed to describe the nickel ion sorption in a fixed bed column, which considered the hydrodynamics throughout the fixed-bed column as well as the sorption process in the liquid and solid phases.
235 citations
TL;DR: In this article, a combination of experiments using physical and chemical methods to characterize mass transfer is presented, showing that both the mass transfer coefficient (kL) and the gas-liquid interfacial area (a) are enhanced in the presence of nanoparticles, the latter accounting for a large fraction of the total enhancement.
Abstract: Venue, Cambridge, Massachusetts 02139 Oxygen-transfer enhancement has been observed in the presence of colloidal dispersions of magnetite (Fe3O4) nanoparticles coated with oleic acid and a polymerizable surfactant. These fluids improve gas-liquid oxygen mass transfer up to 6-fold (600%) at nanoparticle volume fractions below 1% in an agitated, sparged reactor and show remarkable stability in high-ionic strength media over a wide pH range. Through a combination of experiments using physical and chemical methods to characterize mass transfer, it is shown that (i) both the mass transfer coefficient (kL) and the gas-liquid interfacial area ( a) are enhanced in the presence of nanoparticles, the latter accounting for a large fraction of the total enhancement (80% or more), (ii) the enhancement in kL measured by physical and chemical methods is similar and ranges from 20 to 60% approximately, (iii) the enhancement in kL levels off at a nanoparticle volume fraction of approximately 1% v/v, and (iv) the enhancement in kLa shows a strong temperature dependence. These results are relevant to a wide range of processes limited by the mass transfer of a solute between a gas phase and a liquid phase, such as fermentation, waste treatment, and hydrogenation reactions.
208 citations
TL;DR: Novel bio-sorbent wheat bran has been successfully utilized for the removal of cadmium(II) from wastewater and it has been found that the reaction was spontaneous and exothermic in nature.
161 citations
TL;DR: In this paper, the effect of surfactants on the mass transfer parameters (volumetric mass transfer coefficient kLakLa and liquid-side mass transfer coefficients kL)kL) was investigated.
153 citations
TL;DR: In this article, a two-dimensional analysis of heat and mass transfer during drying of a rectangular moist object is performed using an implicit finite difference method, with the convective boundary conditions at all surfaces of the moist object.
136 citations
TL;DR: Mass transfer models on supercritical carbon dioxide extraction of vegetable oils are reviewed, that may facilitate the scale-up of laboratory data for industrial design purposes and the role of the solid matrix on high-pressure phase equilibrium is given.
Abstract: Mass transfer models on supercritical carbon dioxide (SC-CO 2 ) extraction of vegetable oils are reviewed, that may facilitate the scale-up of laboratory data for industrial design purposes. Reviewed mechanisms of oil transport within the solid matrix include the desorption from the solid, the formation of a shrinking core of condensed oil in a non-adsorbing porous matrix, and diffusion in a homogenous medium. Analyzed simplificat ions of a general mass transfer model include external control of mass transfer rates, internal control of mass transfer rates, consideration of a linear driving force, and steady state approximations, among others. More complex two-stage models, and critical comparisons of some of the proposed models are also included. Trends for the external mass transfer coefficient and effective diffusivity in the solid matrix from studies on SC-CO 2 extraction of oil from vegetable substrates are thoroughly discussed and contrasted with those obtained using simpler model systems. The possib...
136 citations
TL;DR: In this article, the authors present a summary of the work in these areas as found in the literature dating back to 1949 and provide a critical review to guide the selection of the best correlation(s) in circulating fluidized bed reactors.
126 citations
TL;DR: In this paper, the mass transfer resistances of all the physical domains composing the air-gap membrane distillation (AGMD) and DCMD processes are developed and their absolute and relative effects are evaluated to improve the process understanding and identify promising ways for its improvement.
123 citations
TL;DR: This work confirms that eddy diffusion originated from three different sources in RPLC: trans-channel, short-range interchannel, and long-rangeInterchannel velocity biases, and shows excellent agreement between the experimental and theoretical HETP equations.
Abstract: Classical HETP equations including the Van Deemter and the Knox equations, are semiempirical, approximate equations that provide apparent mass-transfer coefficients with little sound physical justifications. The conventional A and B coefficients are revisited, the former through the use of the fundamental theory of eddy diffusion due to Giddings, the latter by taking into account the intraparticle diffusion (pore and surface diffusion). Our work confirms that eddy diffusion originated from three different sources in RPLC: trans-channel, short-range interchannel, and long-range interchannel velocity biases. Accordingly, the eddy diffusion term is given by the ratio of two third-degree polynomials. Finally, the C term is the sum of two terms corresponding to the resistance to mass transfer due to diffusion through the external stationary film of liquid phase surrounding the silica particles and to the classical resistances to mass transfer due to diffusion through the silica particles. It is easily related...
118 citations
TL;DR: The effect of ultrasound on the leaching process, in which Geniposide is leached from the Gardenia fruit by deionized water at 20 degrees C, was investigated and the dynamic curves calculated by the model are in a good agreement with the experimental data.
111 citations
TL;DR: In this article, the authors evaluate mass transfer effects on the characterization and specification of aeration systems in clean and process water conditions, and find that contamination effects can be offset at the expense of operating efficiency.
TL;DR: The proposed mathematical model of the biosorption process was capable of demonstrating the expanding and broadening of the mass transfer zone linked to the equilibrium sorption isotherm, particularly important for process scale-up where maintaining the process efficiency is critical.
Abstract: Modeling of the mass transfer zone behavior under variable conditions in a flow-through fixed-bed sorption column enabled the prediction of breakthrough curves for Cu2+ and Ca-preloaded Sargassum fluitans biomass. The mass transfer resistance, particle diffusion, and the axial dispersion were incorporated in the model. The dynamics of the mass transfer zone was described under variable sorption column operating conditions including different column lengths and fluid flow rates. Accurate estimation of the behavior of the mass transfer zone as it progressed through the column, reflected eventually in the breakthrough curve, assisted in its relevant interpretations. Furthermore, the proposed mathematical model of the biosorption process was capable of demonstrating the expanding and broadening of the mass transfer zone linked to the equilibrium sorption isotherm. The fundamental understanding of the mass transfer zone dynamics is particularly important for process scale-up where maintaining the process effic...
TL;DR: In this article, experimental and modeling results are presented of the liquid holdup and gas-to-liquid mass transfer characteristics of solid foam packings in a semi-2D transparent bubble column with aluminum in the range of 5-40 pores per inch (ppi).
Abstract: In this paper, experimental and modeling results are presented of the liquid holdup and gas–liquid mass transfer characteristics of solid foam packings. Experiments were done in a semi-2D transparent bubble column with solid foam packings of aluminum in the range of 5–40 pores per inch (ppi). The relative permeability model described by Saez and Carbonell (1985) is used to describe the liquid holdup data for solid foam packings of 5, 20 and 40 ppi. The investigated system variables are the superficial gas and liquid velocities, using counter-current flow with maximum gas velocities and liquid velocities of 0.8 m s −1 and 0.03 m s −1 , respectively. The relative permeability model is able to describe the liquid holdup in the low liquid holdup or trickle flow regime as well as in the high liquid holdup regime, which resembles flow in a packed bubble column. Gas-to-liquid mass transfer is modelled using the penetration theory. Mass transfer coefficients up to 6 s −1 are predicted; these high values are largely due to the high specific surface area of the solid foam packings.
TL;DR: In this article, a complex computational mass transfer model (CMT) is proposed for modeling the chemical absorption process with heat effect in packed columns, which is able to predict the concentration and temperature as well as the velocity distributions at once along the column without assuming the turbulent Schmidt number, or using the experimentally measured turbulent mass transfer diffusivity.
TL;DR: In this paper, an experimental and theoretical study has been conducted on the adsorption kinetics of ethanol onto a pitch-based activated carbon fiber (ACF) of type (A-20).
TL;DR: In this article, the breakthrough behavior of an activated carbon bed fed with constant concentrations of organic vapors and a stepped concentration of water vapor is investigated for a single carbon bed with both hydrophobic and hydrophilic organics considered.
Abstract: Breakthrough behavior is investigated for an activated carbon bed fed with constant concentrations of organic vapors and a stepped concentration of water vapor. The organics are present as single components and binary mixtures, with both hydrophobic and hydrophilic organics considered. Experiments are performed using a fully automated fixed-bed apparatus, which enables breakthrough curve studies for gas mixtures over a wide range of concentrations, from much less than 1 ppm up to saturation. The adsorbed-phase mass transfer coefficient of water is found to be a strong function of water loading. The system response is complex, with behaviors for hydrophilic and hydrophobic compounds being quite different. A model incorporating an accurate description of the highly nonideal adsorption equilibria is developed to simulate all of the fixed-bed experiments and gives good agreement in time, trend, extent, and shape of the breakthrough curves.
TL;DR: In this paper, the mass transfer coefficients for CO2 and a nonreactive gas, CH4, in an experimentally eutrophied lake were estimated using floating chambers.
Abstract: [1] At high pH the chemical reaction of CO2 with OH− can significantly increase the mass transfer of CO2 between air and water. The reaction of CO2 with OH− strongly fractionates carbon isotopes in comparison to simple diffusion. These processes, chemically enhanced diffusion (CED) and chemically enhanced fractionation (CEF), greatly influence the carbon budgets and carbon isotope ratios for water bodies with high pH. Using floating chambers, we estimated mass transfer coefficients for CO2 and a nonreactive gas, CH4, in an experimentally eutrophied lake. The mass transfer coefficient estimated from CH4 flux did not vary greatly between measurements (k600 = 1.83 ± 0.33 cm h−1; mean ±1 SD) and agreed well with other independent estimates of mass transfer. The mass transfer coefficient of CO2, however, was chemically enhanced by 3.5- to 7.5-fold. This enhancement was related to pH and temperature but was slightly higher than predictions from an existing model. We determined the role of CEF by modifying a model of CED to include both carbon isotopes (12C and 13C). A whole-lake addition of inorganic 13C to Peter Lake created dynamics in δ13C-dissolved inorganic carbon (DIC) and provided a test of the new model. The value of δ13C-DIC decreased from approximately −9‰ to −21‰, a result that was well predicted by the model including CEF but could not be duplicated when CEF was omitted. Thus CED and CEF influenced the mass balance of air-water CO2 exchange and had isotopic consequences for DIC. Although CEF is considered inconsequential for mean oceanic conditions, this model could be applied to marine systems for inorganic carbon modeling in areas where pH is elevated or physical mass transfer is limited because of low turbulence.
TL;DR: In this article, a unique approach to simulate mass transfer across the moving droplet where mass transport equations and governing equations of the levels set method are solved separately is proposed in order to track the motion of the interface.
TL;DR: In this paper, the hydrodynamic characteristics of gas-liquid slug flow in an upward tube are investigated with limiting diffusion current probes, conductivity probes and digital high-speed video system.
TL;DR: In this paper, the absorption of oxygen and styrene in water-silicone oil emulsions was independently studied in laboratory-scale bubble reactors at a constant gas flow rate for the whole range of emulsion compositions (0-10% v/v).
TL;DR: In this paper, the impacts of operating conditions and liquid properties on the hydrodynamics and volumetric mass transfer coefficient in activated sludge air-lifted reactors were investigated.
Abstract: This study was to investigate the impacts of operating conditions and liquid properties on the hydrodynamics and volumetric mass transfer coefficient in activated sludge air-lift reactors. Experiments were conducted in internal and external air-lift reactors. The activated sludge liquid displayed a non-Newtonian rheological behavior. With an increase in the superficial gas velocity, the liquid circulation velocity, gas holdup and mass transfer coefficient increased, and the gas residence time decreased. The liquid circulation velocity, gas holdup and the mass transfer coefficient decreased as the sludge loading increased. The flow regime in the activated sludge air-lift reactors had significant effect on the liquid circulation velocity and the gas holdup, but appeared to have little impact on the mass transfer coefficient. The experimental results in this study were best described by the empirical models, in which the reactor geometry, superficial gas velocity and/or power consumption unit, and solid and fluid properties were employed.
TL;DR: In this article, a T-shaped microchannel with 600μm wide and 200μm deep in continuous phase and 70mm wide and 20mm deep in dispersed phase by flowing two immiscible solutions, buffer solution containing aluminum and tributyl phosphate as dispersed phase.
TL;DR: In this paper, the authors investigated the effect of swirling on the overall gas phase mass transfer coefficient, Kga, for both swirling and non-swirling axial gas flows in a spray tower.
Abstract: Spray towers are commonly used in the chemical and process industries for a number of applications including absorption, desorption and humidification. However, the main disadvantage of a spray tower compared with that of a packed tower is its lower contact efficiency. The present study is concerned with the enhancement of mass transfer between a continuous gas phase and liquid droplets in a spray tower by imparting swirl to the axial gas flow through the tower. It is well known that swirling flow has the ability to augment the rates of heat and mass transfer. Experimental investigations into the hydrodynamics and mass transfer in a laboratory-scale spray tower for air-NH3/H2O system using axial and swirling gas flows have been carried out. The hydrodynamic studies included measurements of the gas velocity distributions and overall pressure drop in the tower, and characterization of water sprays generated by a pressure-swirl nozzle where radial liquid distributions, droplet size and its distribution and mean droplet size in terms of SMD were measured. As for the mass transfer performance of the spray tower, the effect of the gas and liquid flow rates on the overall gas phase mass transfer coefficient, Kga, was investigated for both swirling and non-swirling axial gas flows in order to quantify the effect of swirl. It has been found that Kga increases with increasing gas/liquid flow rates and imparting swirl in the gas flow enhances Kga up to 20% compared with that in axial flows. Correlations of Kga as a function of the gas/liquid flow rates, and also as a function of the gas flow rate and initial droplets SMD are developed. A design methodology to determine the height of a spray tower required to achieve a specified amount of removal of a solute from a gas mixture is proposed.
TL;DR: In this article, the authors compared the performance of PDMS and poly (methyl vinyl) siloxane (PVMS) in the membrane extraction of water-phenol mixtures and found that PDMS was more suitable for the operation under strong base condition.
TL;DR: In this paper, a correlation for the volumetric gas-liquid mass transfer coefficient (kLa) in stirred-tank reactors (STRs) using results from the literature is developed.
Abstract: A correlation is developed for the volumetric gas–liquid mass transfer coefficient (kLa) in stirred-tank reactors (STRs) using results from the literature. The volumetric mass transfer coefficient is correlated on the basis of the relative dispersion parameter (N/NCD) for similar impeller hydrodynamics and operating regimes. Using a bench-top STR of diameter T= 0.211 m, gas–liquid mass transfer data are also obtained and found to follow the proposed correlation when the appropriate hydrodynamic conditions are satisfied. A STR scale-up technique from bench-scale (T= 0.211m and D/T= 0.35) to industrial-scale (up to T= 2.7 m) is proposed using a normalized hydrodynamic flow regime map and shown to be useful in understanding the range of operational conditions for the successful scale-up of STRs.
TL;DR: In this paper, the drying kinetics of carrot cubes were carried out at 1 m/s air velocity at different air drying temperatures (30, 40, 50, 60 and 70±0.1 °C) and also at the same experimental conditions but applying high power ultrasound (US experiments).
Abstract: Drying kinetics of carrot cubes were carried out at 1 m/s air velocity at different air drying temperatures (30, 40, 50, 60 and 70±0.1 °C) (AIR experiments), and also at the same experimental conditions but applying high power ultrasound (US experiments). Two kind of diffusion models were used to simulate the drying kinetics, according to external resistance to mass transfer being considered (ER model) or neglected (NER model) for solving the diffusion equation. Diffusion ER model was solved using a finite difference method. Drying rate increased as air temperature was higher. Ultrasound also increased drying rate at the different temperatures, but the improvement on drying rate decreased at high temperatures, and almost disappeared at 70 °C. Effective moisture diffusivities only showed an Arrhenius type relationship with temperature for AIR experiments. The NER diffusion model was not accurate to simulate the drying kinetics at any experimental conditions tested. However, diffusion ER model provided a high closeness between experimental and calculated drying data (VAR>99.80). Through the parameters identified of the ER diffusion model, effective moisture diffusivity and mass transfer coefficient, the influence of the power ultrasound application on internal and external resistance to mass transfer was shown to be significant (p
TL;DR: The characterization equations make it possible to predict the gas transfer that will occur across bubble interfaces and across the free surface with a bubble plume at depths up to 32 m and with variable air discharge in deep tanks and reservoirs.
TL;DR: In this article, an attempt has been made to evaluate the convective mass transfer coefficient during drying of Jaggery in a controlled environment for natural as well as forced convection, in which the Jaggery was dried in the roof type even span greenhouse with floor area of 1.78m2.
TL;DR: In this article, a laboratory scale direct contact condenser has been fabricated as a twin tower structure with two stages, co-current and countercurrent, and experiments have been operated in each stage with respective saturated air inlet temperatures of 36, 40 and 43 °C.