Showing papers on "Mass transfer coefficient published in 1984"

Mass Transfer: Fundamentals and Applications

Abstract: 1. Mass Transfer Fundamentals. 2. Diffusion Coefficients. 3. Formulation of Mass Transfer Models. 4. Partial Differential Equations of Diffusion. 5. Mass Transfer Coefficients. 6. Convective Mass Transfer. 7. Phase Equilibrium. 8. Adsorption. 9. Binary Distillation. 10. Multicomponent Distillation. 11. Extraction. 12. Mass Transfer in Continuous Differential Contactors. 13. Design of Staged Columns. 14. Adsorption. Appendix A: Viscosity of Gases and Liquids. Appendix B: Equilibrium Data. Appendix C: Equilibrium K-Values. Appendix D: Enthalpy Data. Appendix E: Unit Conversion Factors and Constants.

Hydrodynamics and mass transfer in non‐Newtonian solutions in a bubble column

Abstract: Until now the oxygen transfer in viscous non-Newtonian solutions has been studied only in bubble columns of about 0.14-m diameter. Recently Godbole et al. (1982) reported much smaller gas holdups in Carboxy Methyl Cellulose solutions (CMC) for a large-diameter column. Therefore, the gas holdups, volumetric mass transfer coefficients, and specific gas-liquid interfacial areas are measured in CMC solutions using a bubble column of diameter 0.305 m and height 3.4 m. The transition from churn-turbulent to slug flow regime occured at higher viscosities and the gas holdups and volumetric mass transfer coefficients were lower in both flow regimes than reported for smaller column diameters. Empirical correlations are presented for the gas holdup, volumetric mass transfer coefficient, and specific gas-liquid interfacial area which would be suitable for the design of fermentors.

The Variation of the Gas Transfer Coefficient with Molecular Diffusity

Abstract: We argue that the boundary conditions at the air-water interface lead to a variation of the transfer coefficient with the 1/2 power of the molecular diffusivity for slightly soluble gases. For wind-driven bodies of water the transfer coefficient should vary with the −1/2 power of the Schmidt number and with the 1/2 power of that part of the wind stress transmitted by viscosity. The boundary conditions are contrasted with those at a smooth wall where the mass transfer coefficient varies with the –2/3 power of the Schmidt number. Measurements of the transfer coefficient for N2O, CH4, and He at moderate wind stress in an 18 meter wind-wave tunnel support our arguments.

Gas holdup and volumetric liquid-phase mass transfer coefficient in solid-suspended bubble columns

Abstract: The effects of column dimensions, gas velocity and the properties of liquid and solid particles on the gas holdup eG and the volumetric liquid-phase mass transfer coefficient kLa in the solid-suspended bubble column of liquid-solid batch operation were studied experimentally. The presence of suspended solid particles in the bubble column reduces values of eG and kLa, and their reduction by an addition of solid particles to the column is high in the transition regime and low in the heterogeneous flow regime. Based on these observations, empirical equations for eG in transition flow and in heterogeneous flow, and an empirical equation for kLa a applicable to the above two flow regimes are proposed.

Analytical solution using a pore diffusion model for a pseudoirreversible isotherm for the adsorption of basic dye on silica

Abstract: An analytical solution for a two resistance mass transfer model explaining the adsorption of Astrazone Blue dye (Basic Blue 69) onto Sorbsil silica has been developed. The model includes a film mass transfer coefficient, kf1 = 80 × 10−6cm·s−1, and an internal effective diffusivity, Deff = 18×10−9cm2·s−1 which controls the internal mass transport processes based on a pore diffusion mechanism.

The concept of interfacial reactions for mass transfer in liquid/liquid systems

Abstract: Interfacial reactions during reactive mass transfer between liquid phases are the central point of this contribution. In order to go from the general problem to identify the site of the reaction and the rate-controlling step, a kinetic treatment of interfacial reactions is proposed that considers the individual processes of all the species involved. This concept, together with a new method for the determination of individual transport coefficients, leads to an efficient concept of resistances and to the possibility of treating chemically coupled systems (coextraction). Finally, the pronounced effects of adsorption layers are discussed with respect to diffusional- and interfacial-controlled mass transfer.

Performance of the gas bubble column in molten salt systems

Abstract: Experimental data on the gas holdup and the mean bubble size in a bubble column with a single nozzle was obtained for gas-molten salt systems of a eutectic mixture of LiCl (58 mol %)-KCl (42 mol %) and molten NaNO/sub 3/. The liquid-phase mass transfer coefficient K /SUB L/ was evaluated from the specific surface area a and the volumetric coefficient K /SUB L/ a data for oxygen and carbon dioxide absorption into molten NaNO/sub 3/. The dimensionless correlations of the performance of bubble columns for aqueous solutions can be extended to the gas-molten salt systems.

A Standard for the Measurement of Oxygen Transfer in Clean Water

Abstract: This standard was developed to measure the rate of oxygen transfer from diffused gas and mechanical oxygenation devices to water. The standard is applicable to laboratory scale oxygenation devices with water volumes of a few gallons as well as to full scale systems with water volumes typical of those found in the activated sludge wastewater treatment process. It is intended that this standard be used in the preparation of specifications for compliance testing and in the development of performance information. This test method is based upon removal of dissolved oxygen (DO) from the water volume by sodium sulfite followed by reoxygenation to near the saturation level. The DO inventory of the water volume is monitored during the reaeration period by measuring DO concentrations at several points selected so that each point senses an equal tank volume. The method specifies a minimum number, distribution and range of DO measurements at each point. The data obtained at each determination point are analyzed by a simplified mass transfer model to estimate the apparent volumetric mass transfer coefficient and the saturation concentration. Nonlinear regression is employed to fit the model to the DO profile measured at each point during reoxygenation. Estimates are adjusted to standard conditions and the standard oxygen transfer rate is obtained. A procedure based on the clean water test results is recommended for estimation of oxygen transfer rates under process conditions. Various components of power consumption are defined and methods for measurement of gas rate and power consumption by the oxygenation device are given. Energy efficiency of the oxygenation device is evaluated as the mass rate of oxygen transferred per unit power consumed.

Desorption of carbon dioxide from supersaturated water in an agitated vessel

Abstract: The rates of desorption of carbon dioxide from supersaturated water solutions into pure carbon dioxide or nitrogen gas stream were measured at 15,25, and 35°C in a baffled agitated vessel with a flat gas-liquid interface operated in a continuous manner. The volumetric liquid-phase mass transfer coefficients for the bubbles generated in the agitated liquid and the enhancement factors of the volumetric liquid-phase mass transfer coefficient for the free liquid surface due to the bubbling were calculated from the measured desorption rates and correlated as functions of the relative supersaturation of the solution and the liquid-phase Reynolds number.

Fluid flow and mass transfer in an inductively stirred four-ton melt of molten steel: A comparison of measurements and predictions

Abstract: Experimental measurements are reported on melt velocities and on the rate at which immersed carbon rods dissolve in a 4-ton induction furnace, holding a low carbon steel melt. These measurements are compared with theoretical predictions, based on the numerical solution of Maxwell’s equations and the turbulent Navier-Stokes equations. In general, good agreement has been obtained, both regarding the absolute values of the velocities and the mass transfer coefficients and the trends predicted by the theoretical analysis. In addition to providing further proof regarding the applicability of the mathematical modeling technique, the principal contribution of the work is that it provides an improved insight into the behavior of inductively stirred melts. In particular it was found that for an inductively stirred melt both the velocities and the rate of turbulence energy dissipation are relatively uniform spatially, in contrast to bubble stirred systems, where most of the agitation is confined to the jet plume and to the near surface region. It was found, furthermore, that the mass transfer coefficient characterizing the rate of dissolution of immersed carbon rods depends both on the absolute values of the melt velocity and on the local values of the turbulence intensity; thus significant mass transfer will occur in the region of the eye of the circulation, where the absolute value of the mean velocity is small.

Oxygen mass transfer in a bubble column bioreactor containing lysed yeast suspensions

Abstract: Liquid-phase volumetric oxygen transfer coefficients were evaluated in a bubble column containing yeast suspensions, using the instationary oxygen absorption method and a polarographic oxygen electrode. The electrode time lag was found to be independent of both the system studied and the operating conditions. The volumetric oxygen mass transfer coefficients k L a could be reasonably predicted by calculating k L from the equation derived by Bhavaraju et al. or the empirical equation of Calderbank and Moo-Young and “a” from the experimental gas hold-up values.

Modeling of Liquid-Membrane Extraction Processes

Abstract: A general mathematical model containing overall mass transfer coefficients for extraction and leakage has been developed for extractions by liquid surfactant membranes (LM). In this model, two extraction cases are considered—one has chemical reagent in the external feed phase to convert the leaking species into an extractable form for re-extraction into the LM emulsion, the other does not have reagent in the external phase. Most LM extraction systems can be classified into these two cases. Mass transfer equations to calculate solute recovery, contact time, extractor size, and chemical reagent consumption in relation to overall mass transfer coefficients have been derived and can be used to predict the extraction performance of a continuous LM process from a simple batch extraction experiment. It is shown from the model that the reagent for chemical conversion in the external phase can enhance extraction greatly and can minimize the effect of leakage on extraction significantly. This model has been applied successfully to experimental data in LM extractions, such as separations of chromium and phenol from their aqueous solutions.

Ozone Mass Transfer in Stirred Vessel

Abstract: A method is proposed and a model is developed which are capable of providing a correlation of the mass transfer coefficient kLa, with stirrer speed and gas superficial velocity. The method can be adopted for deriving a correlation which can be profitably used for ozone gas–liquid reaction both for assessing the absorption regime and for the simulation of oxidation processes which evolve according to slow reaction regime.

Influence of hydrodynamics on crystal growth and dissolution in a fluidized bed

Abstract: Mass transfer coefficients for the growth and the dissolution of potassium alum and sodium thiosulfate in a laboratory-scale fluidized-bed apparatus were determined and correlated in a form of the Frossling equation. The surface reaction rate for potassium alum was found to be dependent onthe crystal size.

Mass Cultivation of Catharanthus roseus Cells Using a Nonmechanically Agitated Bioreactor

Abstract: Batch suspension cultures ofCatharanthus roseus G. Don were grown in a 5 L LKB Ultraferm fermenter, converted to operate as an airlift bioreactor, to test the suitability of such a system for the mass culture of plant cells. Results show that the airlift system has considerable merits as a culture vessel for such a purpose, including: conversion rates of carbohydrate substrate to cell mass equivalent to > 50% under optimum conditions. (Operating under these conditions, growth rates of approximately 0.4 d-1 are typical). In the absence of the mechanical shear normally associated with mechanically driven bioreactors, the gently agitated environment of the airlift vessel proves to be an ideal system for the growth of fragile plant cells. Use of a nozzle sparger reduces the possibility of a high mass transfer coefficient, except at very high gassing rates, thereby eliminating any interference with the growth rate caused by high rates of gaseous exchange.

Contribution of oscillating mass transfer to the photoacoustic effect

Abstract: In a gas‐microphone cell absorption of modulated light causes oscillating transport of heat and of mass as well. The transport of mass is described by the diffusion equation. The concentration of substance from sample or sorbate at the sample to gas boundary is obtained from the vapor pressure. Introduction of an average molar concentration variation leads to a pressure variation. Results of calculations can explain recently measured data very well. For water at 40 °C oscillating mass transfer contributes the same amount to pressure variation as the heat wave.

Mass transfer characteristics of electrochemical reactors employing gas evolving mesh electrodes

Abstract: Mass transfer rates were measured at a single screen and a fixed bed of closely packed screens for the simultaneous cathodic reduction of K3Fe(CN)6 and anodic oxidation of K4Fe(CN)6 in alkaline solution with H2 and O2 evolution, respectively. Variables studied were gas discharge rate, number of screens per bed and position of the electrode (vertical and horizontal). For single screen electrodes, the mass transfer coefficient was related to the gas discharge rate by the equations: $$\begin{gathered} K = aV^{0.190} , for H_2 evolving electrodes, \hfill \\ K = aV^{0.469} , for O_2 evolving electrodes \hfill \\ \end{gathered} $$ . Electrode position was found to have no effect on the rate of mass transfer for single and multiscreen electrodes in the case of H2 and O2 evolution. Mass transfer coefficients were found to increase with an increasing number of screens per bed in the case of H2 evolution, while in the case of O2 evolution the mass transfer coefficient decreased with an increasing number of screens per bed. A mathematical model was formulated to account for the behaviour of the H2 evolving electrode which, unlike the O2 evolving electrode, did not obey the penetration model. Power consumption calculations have shown that the beneficial effect of mass transfer enhancement is outweighed by the increase in the voltage drop due to gas evolution in the bed electrode.

Kinetics of the Desorption of Ammonia from Water by Diffused Aeration

Abstract: Ammonia desorption by diffused aeration was investigated in a lab-scale, batch aeration column, and the theoretical basis for the operation was developed. A formula was derived for the calculation of the fraction of ammonia present in the solution in undissociated form (susceptible for desorption) for any given temperature and pH. The experimental work shows that desorption is equilibrium controlled, which is at variance with some of the results reported in the literature. Lower limits of the ammonia mass transfer coefficient for bubbles rising through the water column were estimated. The impact of the surface effect on the rate of desorption was taken into account in the calculations.

The Ratio of Gas-Phase to Liquid-Phase Mass Transfer Coefficients in Gas-Liquid Contacting Processes

Abstract: The results of multicomponent experiments with mass transfer at the air-water interface are analyzed using the indirect approach of fitting overall mass transfer rate constants to the two-resistance model with appropriate corrections for molecular diffusivities. We show that the ratio of mass transfer coefficients (kG/kL) is significantly smaller than the suggested value of kG/kL = 150 customarily used to model surface aeration, bubble aeration, and countercurrent packed columns. Hence the gas-phase resistance has been underestimated, which can lead to the overestimation of overall mass transfer rate constants. Also, kG/kL varies for a given process depending on the hydrodynamic conditions.