Showing papers on "Mass transfer published in 1986"
TL;DR: In this paper, the mass transfer correlations reported in this paper are similar to earlier heat and mass transfer correlation, but can be complicated by diffusion across the fiber wall and by alterations in fiber geometry.
Abstract: Hollow-fiber contactors can provide fast mass transfer without flooding or loading. They are a promising alternative to packed towers for gas treating, and to centrifugal extractors for liquid-liquid extraction. Hollow-fiber contractors can be designed effectively using the mass transfer correlations reported in this paper. The correlations, based on aqueous deaeration and carbon dioxide absorption, are similar to earlier heat and mass transfer correlations, but can be complicated by diffusion across the fiber wall and by alterations in fiber geometry.
592 citations
TL;DR: In this article, a model which includes the transport and retardation mechanisms of advective flow, axial dispersion, liquid-phase mass transfer, diffusion into immobile liquid, and local adsorption equilibrium was developed to describe the migration of nondegradable, organic chemicals through a column of saturated, aggregated soil.
Abstract: A model which includes the transport and retardation mechanisms of advective flow, axial dispersion, liquid-phase mass transfer, diffusion into immobile liquid, and local adsorption equilibrium was developed to describe the migration of nondegradable, organic chemicals through a column of saturated, aggregated soil. A range of simplifying assumptions were explored to assess the relative importance of the various mechanisms. Solutions to the model were either adapted from the literature or derived from mass balances and mass transfer principles. The most general form of the model required the development of numerical solutions which employed orthogonal collocation. Soil column breakthrough predictions in terms of relative concentration as a function of total column pore volumes fed can be characterized by seven independent dimensionless parameters: the Peclet number, the Stanton number, a pore diffusion modulus, a surface diffusion modulus, an adsorbed solute distribution ratio, an immobile fluid solute distribution ratio, and the Freundlich parameter 1/n. For a strongly adsorbed chemical in long soil columns, a fifteen fold decrease of the Peclet number, a fivefold decrease of the Stanton number, or a onefold decrease in either the pore diffusion modulus or the surface diffusion modulus have an equivalent effect on the spreading of the breakthrough curve. The breakthrough curve tends to sharpen for favorably adsorbed chemical species (1/n 1.0). The movement of chemical is retarded as the solute distribution ratios increase. A sensitivity analysis of model parameters, which were derived from literature correlations, column geometry, soil adsorption isotherms, and breakthrough curves, showed that adsorption capacity, adsorption intensity, and aggregate geometry have the greatest effect on chemical retardation and spreading, while liquid-phase mass transfer has little effect.
263 citations
TL;DR: In this article, a multigrain particle model was used to describe polypropylene and ethylene polymerization in liquid and gas media. Intraparticle heat and mass transfer effects were investigated for a range of catalyst activities.
Abstract: Propylene and ethylene polymerization in liquid and gas media are described by a multigrain particle model. Intraparticle heat and mass transfer effects are investigated for a range of catalyst activities. For slurry polymerization, intraparticle mass transfer effects may be significant at both the macroparticle and microparticle level; however, for normal gas phase polymerization, microparticle mass transfer effects appear more likely to be important. Intraparticle temperature gradients would appear to be negligible under most normal operating conditions.
203 citations
TL;DR: It is suggested that chemicals with high Henry's law constants, but have low vapor pressures and are thus subject to appreciable sorption to atmospheric particles, may cycle between water and air with intermittent periods of intense deposition followed by slower but prolonged volatilization.
Abstract: A comprehensive model is developed describing the rates of processes of organic chemical volatilization, absorption at the water surface, dissolution in rainfall, and wet and dry particle deposition, which in total comprise the dominant air-water exchange processes. Correlations are suggested for partitioning between air and airborne particles and for washout ratios as a function of the chemical's physical-chemical properties. It is suggested that chemicals with high Henry's law constants, which are subjected to volatilization, but have low vapor pressures and are thus subject to appreciable sorption to atmospheric particles, may cycle between water and air with intermittent periods of intense deposition followed by slower but prolonged volatilization. A steady-state but non-equilibrium condition may be achieved in which the water is supersaturated with respect to the air; i.e., the chemical potential or fugacity of the chemical in the water exceeds that in the air. These effects will be pronounced at low temperatures. 34 references, 1 figure, 4 tables.
166 citations
TL;DR: In this paper, an analytical and numerical study of natural convection heat and mass transfer through a vertical porous layer subjected to uniform fluxes of heat from the side is presented, which is driven by the combined buoyancy effect due to temperature and concentration variations through the porous medium.
163 citations
TL;DR: Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1985 as discussed by the authors, Boston, Massachusetts, United States of America, Boston, MA
Abstract: Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1985.
140 citations
TL;DR: In this article, mass transfer at carbon fibre electrodes has been studied using the mass transfer controlled reduction of potassium hexacyanoferrate(III) to KHN(II) in a flow-by-mode.
Abstract: Mass transfer at carbon fibre electrodes has been studied using the mass transfer controlled reduction of potassium hexacyanoferrate(III) to potassium hexacyanoferrate(II). Different geometrical configurations have been assessed in a flow-by mode, namely bundles of loose fibres with liquid flow parallel to the fibres, carbon cloth with flow parallel to the cloth and carbon felt with liquid flow through the felt. For comparison, mass transfer rates at a single fibre have been measured; the experimental data fit the correlationSh=7Re
0.4. The same correlation can be used as a first approximation for felts. Mass transfer for fibre bundles and cloth under comparable conditions is much lower owing to channelling.
135 citations
TL;DR: In this article, a one-dimensional, unsteady state mathematical model was used to obtain the oil concentration profiles in both the solvent and solid phases, and to determine the overall volumetric mass transfer coefficients.
Abstract: Supercritical carbon dioxide extraction of oil from fixed beds (4.8 mm, 24.5 and 12.7 mm I.D.) of crushed canola seeds is described. Experiments were performed to obtain equilibrium data and extraction rates at 55 C, 36 MPa using solvent velocities ranging from 0.04 to 2.8 mm/s. A one-dimensional, unsteady state mathematical model was used to obtain the oil concentration profiles in both the solvent and solid phases, and to determine the overall volumetric mass transfer coefficients. The calculated concentrations and extraction rates are in good agreement with experimental results. The overall volumetric mass transfer coefficient for the initial, constant rate extraction was correlated with interstitial velocity.
122 citations
TL;DR: In this paper, a multigrain particle model was used to describe propylene and ethylene polymerization in liquid and gas media, and external boundary layer heat and mass transfer effects were investigated for various catalysts and operating conditions.
Abstract: Propylene and ethylene polymerization in liquid and gas media are described by a multigrain particle model. External boundary layer heat and mass transfer effects are investigated for various catalysts and operating conditions. For high-activity catalysts used in slurry, external film mass transfer effects may be significant. For gas-phase polymerization of propylene or ethylene, the model predicts significant particle overheating at short times, which may explain the particle sticking and agglomeration problems sometimes observed in industrial reactors.
TL;DR: In this paper, it was shown that the rate of mass transfer of oxygen into an aqueous solution can be enhanced by the presence of small amounts (0.5-1 vol%) of a dispersed organic phase (e.g., hexadecane or cyclohexane), provided that the droplet diameter is in the order of or smaller than the film thickness.
TL;DR: In this article, the intrinsic membrane transfer coefficients of the solute are adequately described by the simple model of unhindered diffusion in tortuous pores developed earlier, and applied pressure difference did not influence the overall solute transfer coefficient as long as it was not close to that required for the breakthrough of aqueous phase into organic phase.
TL;DR: A receding interface model of the drying of single drops of slurries of sodium sulfate decahydrate has been developed to describe the drying characteristics of this material and to estimate the drying rates of particulate slurries as discussed by the authors.
Abstract: A receding interface model of the drying of single drops of slurries of sodium sulfate decahydrate has been developed to describe the drying characteristics of this material and to estimate the drying rates of particulate slurries. The simultaneous heat and mass transfer rate equations have been solved numerically, and the results obtained have been compared with those obtained experimentally by drying single drops suspended on the tip of a glass filament. Single drops of slurries, l.0 to l.5 x 10/sup -3/ m dia., were suspended on the tip of a flexible glass cantilever inserted in a vertical wind tunnel. A 50 ..mu..m dia. nickel wire passed through the center of the glass beam and the outer surface was coated with a thin film of copper, thereby forming a thermocouple that measured the temperature of the core of the drop; the deflection of the beam gave the loss in weight during drying. In this way the instantaneous drying rate and drop temperature were determined and compared with those predicted by the receding interface model. In all cases the agreement between the predictions of the model and experimental results was good.
TL;DR: In this paper, a procedure based on averaging the conservation equations in a homogeneous, disordered fibrous medium is used to demonstrate that in the limit of long times, macroscopic versions of Fick's and Fourier's laws may be used to relate the average flux to the average gradient in driving force.
Abstract: A procedure based on averaging the conservation equations in a homogeneous, disordered fibrous medium is used to demonstrate that in the limit of long times, macroscopic versions of Fick's and Fourier's laws may be used to relate the average flux to the average gradient in driving force. The asymptotic behavior in the limit of low volume fraction of the effective diffusivity (or conductivity) in such a medium is determined for all values of the Peclet number, P = Ua/Df, where U is the average velocity through the bed, a is the fiber radius, and Df is the molecular diffusivity of the solute in the fluid. The convective disturbance caused by the fibers is found to have a large influence on the rate of mass transfer even at moderate Peclet numbers and low volume fraction.
TL;DR: In this paper, the authors examined gas hold-up and mass transfer in a column with and without a draft tube, and found that the introduction of a tube increases gas holdup but decreases the volumetric mass transfer coefficient in Newtonian fluid systems.
Abstract: Gas hold-up and mass transfer were examined in a column with and without a draft tube. It was found that the introduction of a draft tube increases the gas hold-up but decreases the volumetric mass transfer coefficient in Newtonian fluid systems. For non-Newtonian fluid systems, both parameters were increased by the presence of the draft tube. Empirical correlations are proposed for the gas hold-up and the volumetric mass transfer coefficient in the bubble column with Newtonian and non-Newtonian fluid systems. The correlations are in general agreement with the data in this work and in the literature. They should be useful for design and scale-up purposes. It was also found that introduction of an ancillary impeller improves the mass transfer in non-Newtonian fluids due to the break-up of large bubbles.
TL;DR: In this paper, the role of latent heat transfer, in connection with the vaporization of a thin liquid film on a tube's inside surface, in natural convection flows driven by the simultaneous presence of combined buoyancy effects of thermal and mass diffusion is investigated theoretically.
TL;DR: A kinetic model of protein adsorption to gas-liquid interfaces is described in this paper, which is based on a formalism similar to that used to describe proteins at gas-solid interfaces.
TL;DR: A review and critique of the mathematical models which have been developed to describe the mass transfer processes occurring during asymmetric membrane formation in polymeric systems is presented in this article, where the pseudobinary approach enables the decoupling of the mixing rule from the diffusion equations, therefore allowing its separate specification without affecting the validity of the transport model.
Patent•
26 Nov 1986
TL;DR: In this paper, a hollow fiber membrane bioreactor is used to change the flow direction of a nutrient stream passing through a mass transfer chamber, which enhances the transport of metabolic waste from the cells being grown.
Abstract: A mass transfer apparatus and method is based upon use of a mass transfer chamber, such as a hollow fiber membrane bioreactor, with means to change the directional flow therethrough for enhancement of the mass transfer operation. The invention has particular utility in cell growth systems, where the periodic reversal of flow direction of a nutrient stream passed through the bioreactor equalizes dispersion of cell growth through the bioreactor and enhances the transport of metabolic waste from the cells being grown.
TL;DR: In this paper, the axial dispersion model is used to describe the liquid flow when evaluating the solid-liquid mass transfer in co-current two and three-phase fluidized beds of water, air and benzoic acid pellets.
TL;DR: In this paper, a packed tower for aqueous solution-air contacting operations, heat and mass transfer coefficients for each phase are required, and they are correlated with flow rates of air and liquid and the temperature of air.
Abstract: Packed towers can be used for solar regeneration of aqueous solutions and dehumidification of air using aqueous solutions. These processes involve simultaneous heat and mass transfer with heat effects. In order to design a packed tower for aqueous solution-air contacting operations, heat and mass transfer coefficients for each phase are required. For the present study, aqueous calcium chloride solution is used; ceramic Raschig rings and Berl saddles are used as the packing materials. In this paper air phase transfer coefficients are correlated with flow rates of air and liquid and the temperature of air, whereas liquid phase coefficients are correlated with rates of air and liquid flow, and the temperature and concentration of the liquid.
TL;DR: In this article, the erosion-corrosion of vertical 38mm diameter pipes carrying aerated slurry (20 vol% − 30 + 50 mesh silica sand) in 3.13% NaCl solution at 2 to 6 m/s was measured by weight loss measurements over periods of 100 h. The absolute values of the wear rate were sufficiently close to those measured by electrochemical methods and those calculated from a mass transfer correlation determined for this system, Sh=0.031,Re0.83,Sc0.33 to conclude that the dominant mode of metal loss is corrosion
Abstract: The erosion-corrosion of vertical 38-mm diameter pipes carrying aerated slurry (20 vol% − 30 + 50 mesh silica sand) in 3.13% NaCl solution at 2 to 6 m/s has been measured by weight loss measurements over periods of 100 h. Electrochemical methods have been applied to clarify the mechanism of the process and to determine the corrosion component of the metal. Total wear rates in the range of 6 to 25 mm/y were related to the slurry velocity (v) by wear rate=const vn The value of n was in agreement with oxygen mass transfer controlled corrosion being the dominant mode of metal loss, with n ≈ 1. The absolute values of the wear rate were sufficiently close to those measured by electrochemical methods and those calculated from a mass transfer correlation determined for this system, Sh=0.031 Re0.83 Sc0.33 to conclude that the dominant mode of metal loss is corrosion. The role of erosive action in the erosion-corrosion process is to prevent the formation of a complete rust film that normally stifles corros...
TL;DR: In this paper, mass transfer (heavy vapor and small particle deposition) rates to solid walls, including the effects of thermal (Soret) diffusion ('thermophoresis' for small particles), are made by numerically solving the two-dimensional self-similar forced convection laminar boundary-layer equations with variable properties, covering the particle size range from vapor molecules up to the size threshold for inertial (dynamical nonequilibrium) effects.
Abstract: Predictions of mass transfer (heavy vapor and small particle deposition) rates to solid walls, including the effects of thermal (Soret) diffusion ('thermophoresis' for small particles), are made by numerically solving the two-dimensional self-similar forced convection laminar boundary-layer equations with variable properties, covering the particle size range from vapor molecules up to the size threshold for inertial (dynamical nonequilibrium) effects The effect of thermophoresis is predicted to be particularly important for submicron particle deposition on highly cooled solid surfaces, with corresponding enhancement factors at atmospheric conditions being over a thousand-fold at T(w)/T(e) equal to about 06 As a consequence of this mass transfer mechanism, the particle size dependence of the mass transfer coefficient to a cooled wall will be much weaker than for the corresponding case of isothermal capture by Brownian-convective diffusion
TL;DR: In this paper, a mathematical model is developed for the evaporation step in asymmetric membrane casting which allows for the convective transport induced by local film shrinkage because of both solvent loss and the excess volume of mixing effect.
TL;DR: In this paper, a wide range of experimental studies are reported for the adsorption of phenol and p-chlorophenol onto activated carbon in an agitated batch adsorber.
TL;DR: In this paper, the effects of the liquid property and the gas sparging system as well as particle size on the gas holdup and the volumetric liquid-side mass transfer coefficient were determined experimentally.
Abstract: In this work, slurries with suspended fine particles (whose size is smaller than 10 ..mu..m) of lower than 1 wt. % were used to provide an insight into the solid-bubble interaction in a bubble column. The liquid property and the gas sparging system as well as the particle size were varied; the effects of these variables on the gas holdup and the volumetric liquid-side mass transfer coefficient were determined experimentally and are here discussed quantitatively.
TL;DR: Simultaneous heat and mass transfer with phase change in a porous slab has been analytically investigated in this paper, where closed-form analytical expressions for the temperature, vapor concentration, condensation rate and liquid-content distributions as well as the location of the condensation region for each of the two regimes are obtained.
TL;DR: In this paper, the yield of a non-premixed series-parallel reaction at complete conversion was measured in a turbulent, tubular-flow reactor with single and multijet feeds, where the intermediate decreased as mixing was slowed relative to the chemical kinetics, either by decreasing the Reynolds number or by using a less efficient mixing device, or by increasing the feed concentration.
Abstract: The yield of a nonpremixed series-parallel reaction at complete conversion was measured in a turbulent, tubular-flow reactor with single and multijet feeds. The yield of the intermediate decreased as mixing was slowed relative to the chemical kinetics, either by decreasing the Reynolds number, or by using a less efficient mixing device, or by increasing the feed concentration.
Four models, a modified slab model, a modified stretch model, the Harada mass transfer model, and a new closure model, adequately predict the yield when chemical and mixing kinetics are known from independent measurements of the conversion of acid-base reactions. Without modification, the original slab and stretch models are unable to account for the earlier observed invariance of conversion to Schmidt number of very rapid, single-step reactions or to satisfactorily predict the yield of the series-parallel reaction.