Showing papers on "Mass transfer coefficient published in 2007"

Transport Processes and Separation Process Principles (Includes Unit Operations)

Abstract: Preface. I. TRANSPORT PROCESSES: MOMENTUM, HEAT, AND MASS. 1. Introduction to Engineering Principles and Units. Classification of Transport Processes and Separation Processes (Unit Operations). SI System of Basic Units Used in This Text and Other Systems. Methods of Expressing Temperatures and Compositions. Gas Laws and Vapor Pressure. Conservation of Mass and Material Balances. Energy and Heat Units. Conservation of Energy and Heat Balances. Numerical Methods for Integration. 2. Principles of Momentum Transfer and Overall Balances. Introduction. Fluid Statics. General Molecular Transport Equation for Momentum, Heat, and Mass Transfer. Viscosity of Fluids. Types of Fluid Flow and Reynolds Number. Overall Mass Balance and Continuity Equation. Overall Energy Balance. Overall Momentum Balance. Shell Momentum Balance and Velocity Profile in Laminar Flow. Design Equations for Laminar and Turbulent Flow in Pipes. Compressible Flow of Gases. 3. Principles of Momentum Transfer and Applications. Flow Past Immersed Objects and Packed and Fluidized Beds. Measurement of Flow of Fluids. Pumps and Gas-Moving Equipment. Agitation and Mixing of Fluids and Power Requirements. Non-Newtonian Fluids. Differential Equations of Continuity. Differential Equations of Momentum Transfer or Motion. Use of Differential Equations of Continuity and Motion. Other Methods for Solution of Differential Equations of Motion. Boundary-Layer Flow and Turbulence. Dimensional Analysis in Momentum Transfer. 4. Principles of Steady-State Heat Transfer. Introduction and Mechanisms of Heat Transfer. Conduction Heat Transfer. Conduction Through Solids in Series. Steady-State Conduction and Shape Factors. Forced Convection Heat Transfer Inside Pipes. Heat Transfer Outside Various Geometries in Forced Convection. Natural Convection Heat Transfer. Boiling and Condensation. Heat Exchangers. Introduction to Radiation Heat Transfer. Advanced Radiation Heat-Transfer Principles. Heat Transfer of Non-Newtonian Fluids. Special Heat-Transfer Coefficients. Dimensional Analysis in Heat Transfer. Numerical Methods for Steady-State Conduction in Two Dimensions. 5. Principles of Unsteady-State Heat Transfer. Derivation of Basic Equation. Simplified Case for Systems with Negligible Internal Resistance. Unsteady-State Heat Conduction in Various Geometries. Numerical Finite-Difference Methods for Unsteady-State Conduction. Chilling and Freezing of Food and Biological Materials. Differential Equation of Energy Change. Boundary-Layer Flow and Turbulence in Heat Transfer. 6. Principles of Mass Transfer. Introduction to Mass Transfer and Diffusion. Molecular Diffusion in Gases. Molecular Diffusion in Liquids Molecular Diffusion in Biological Solutions and Gels. Molecular Diffusion in Solids. Numerical Methods for Steady-State Molecular Diffusion in Two Dimensions. 7. Principles of Unsteady-State and Convective Mass Transfer. Unsteady-State Diffusion. Convective Mass-Transfer Coefficients. Mass-Transfer Coefficients for Various Geometries. Mass Transfer to Suspensions of Small Particles. Molecular Diffusion Plus Convection and Chemical Reaction. Diffusion of Gases in Porous Solids and Capillaries. Numerical Methods for Unsteady-State Molecular Diffusion. Dimensional Analysis in Mass Transfer. Boundary-Layer Flow and Turbulence in Mass Transfer. II. SEPARATION PROCESS PRINCIPLES (INCLUDES UNIT OPERATIONS). 8. Evaporation. Introduction. Types of Evaporation Equipment and Operation Methods. Overall Heat-Transfer Coefficients in Evaporators. Calculation Methods for Single-Effect Evaporators. Calculation Methods for Multiple-Effect Evaporators. Condensers for Evaporators. Evaporation of Biological Materials. Evaporation Using Vapor Recompression. 9. Drying of Process Materials. Introduction and Methods of Drying. Equipment for Drying. Vapor Pressure of Water and Humidity. Equilibrium Moisture Content of Materials. Rate-of-Drying Curves. Calculation Methods for Constant-Rate Drying Period. Calculation Methods for Falling-Rate Drying Period. Combined Convection, Radiation, and Conduction Heat Transfer in Constant-Rate Period. Drying in Falling-Rate Period by Diffusion and Capillary Flow. Equations for Various Types of Dryers. Freeze-Drying of Biological Materials. Unsteady-State Thermal Processing and Sterilization of Biological Materials. 10. Stage and Continuous Gas-Liquid Separation Processes. Types of Separation Processes and Methods. Equilibrium Relations Between Phases. Single and Multiple Equilibrium Contact Stages. Mass Transfer Between Phases. Continuous Humidification Processes. Absorption in Plate and Packed Towers. Absorption of Concentrated Mixtures in Packed Towers. Estimation of Mass-Transfer Coefficients for Packed Towers. Heat Effects and Temperature Variations in Absorption. 11. Vapor-Liquid Separation Processes. Vapor-Liquid Equilibrium Relations. Single-Stage Equilibrium Contact for Vapor-Liquid System. Simple Distillation Methods. Distillation with Reflux and McCabe-Thiele Method. Distillation and Absorption Efficiencies for Tray and Packed Towers. Fractional Distillation Using Enthalpy-Concentration Method. Distillation of Multicomponent Mixtures. 12. Liquid-Liquid and Fluid-Solid Separation Processes. Introduction to Adsorption Processes. Batch Adsorption. Design of Fixed-Bed Adsorption Columns. Ion-Exchange Processes. Single-Stage Liquid-Liquid Extraction Processes. Types of Equipment and Design for Liquid-Liquid Extraction. Continuous Multistage Countercurrent Extraction. Introduction and Equipment for Liquid-Solid Leaching. Equilibrium Relations and Single-Stage Leaching. Countercurrent Multistage Leaching. Introduction and Equipment for Crystallization. Crystallization Theory. 13. Membrane Separation Processes. Introduction and Types of Membrane Separation Processes. Liquid Permeation Membrane Processes or Dialysis. Gas Permeation Membrane Processes. Complete-Mixing Model for Gas Separation by Membranes. Complete-Mixing Model for Multicomponent Mixtures. Cross-Flow Model for Gas Separation by Membranes. Derivation of Equations for Countercurrent and Cocurrent Flow for Gas Separation for Membranes. Derivation of Finite-Difference Numerical Method for Asymmetric Membranes. Reverse-Osmosis Membrane Processes. Applications, Equipment, and Models for Reverse Osmosis. Ultrafiltration Membrane Processes. Microfiltration Membrane Processes. 14. Mechanical-Physical Separation Processes. Introduction and Classification of Mechanical-Physical Separation Processes. Filtration in Solid-Liquid Separation. Settling and Sedimentation in Particle-Fluid Separation. Centrifugal Separation Processes. Mechanical Size Reduction. Appendices. Appendix A.1. Fundamental Constants and Conversion Factors. Appendix A.2. Physical Properties of Water. Appendix A.3. Physical Properties of Inorganic and Organic Compounds. Appendix A.4. Physical Properties of Foods and Biological Materials. Appendix A.5. Properties of Pipes, Tubes, and Screens. Notation. Index.

Liquid-liquid two-phase mass transfer in the T-junction microchannels

Abstract: In this work, the mass transfer characteristics of immiscible fluids in the two kinds of stainless steel T-junction microchannels, the opposing-flow and the cross-flow T-junction, are investigated experimentally. Water-succinic acid-n-butanol is chosen as a typical example of liquid-liquid two-phase mass transfer process. In our experiments, the mixture velocities of the immiscible liquid-liquid two phases are varied in the range from 0.01 to 2.5 m/s for the 0.4 mm microchannel and from 0.005 to 2.0 m/s for the 0.6 mm microchannel, respectively. The Reynolds numbers of the two-phase mixture vary between 19 and 650. The overall volumetric mass transfer coefficients are determined quantitatively in a single microchannel, and their values are in the ranges of 0.067-17.35 s(-1), which are two or three orders of magnitude higher than those of conventional liquid-liquid contactors. In addition, the effects of the inlet configurations, the fluids inlet locations, the height and the length of the mixing channel, the volumetric flux ratio have been investigated. Empirical correlations to predict the volumetric mass transfer coefficients based on the experimental data are developed. (c) 2007 American Institute of Chemical Engineers AIChE J, 53:3042-3053, 2007.

Direct Contact Membrane Distillation-Based Desalination: Novel Membranes, Devices, Larger-Scale Studies, and a Model

Abstract: We report here direct contact membrane distillation results from modules having 0.28 m2 of membrane surface area employing porous hydrophobic polypropylene hollow fibers of internal diameter (330 μm) and wall thickness (150 μm) with a porous fluorosilicone coating on the outside surface. The brine salt concentration and temperature and the distillate temperature and velocity were varied. Water vapor fluxes approach values obtained earlier in much smaller modules. As the brine temperature was increased from 40 to 92 °C, water vapor flux increased almost exponentially. Increasing the distillate temperature to 60 from 32 °C yielded reasonable fluxes. Salt concentration increases to 10% led to a small flux reduction. An extended 5-day run did not show any pore wetting. A model using the mass transfer coefficient km as an adjustable parameter predicted the brine temperature drop, distillate temperature rise, and water vapor flux well for the large module and the smaller module of 119-cm2 surface area.

A smoothed particle hydrodynamics model for reactive transport and mineral precipitation in porous and fractured porous media

Abstract: [1] A numerical model based on smoothed particle hydrodynamics (SPH) was used to simulate reactive transport and mineral precipitation in porous and fractured porous media. The stability and numerical accuracy of the SPH-based model was verified by comparing its results with analytical results and finite element numerical solutions. The numerical stability of the model was also verified by performing simulations with different time steps and different number of particles (different resolutions). The model was used to study the effects of the Damkohler and Peclet numbers and pore-scale heterogeneity on reactive transport and the character of mineral precipitation and to estimate effective reaction coefficients and mass transfer coefficients. Depending on the combination of Damkohler and Peclet numbers the precipitation may be uniform throughout the porous domain or concentrated mainly at the boundaries where the solute is injected and along preferential flow paths. The effective reaction rate coefficient and mass transfer coefficient exhibited hysteretic behavior during the precipitation process as a result of changing pore geometry and solute distribution. The changes in porosity and fluid fluxes resulting from mineral precipitation were also investigated. It was found that the reduction in the fluid flux increases with increasing Damkohler number for any particular reduction in the porosity. The simulation results show that the SPH, Lagrangian particle method is an effective tool for studying pore-scale flow and transport. The particle nature of SPH models allows complex physical processes such as diffusion, reaction, and mineral precipitation to be modeled with relative ease.

Recovery of Ammonia from Human Urine by Stripping and Absorption

Abstract: Separately collected human urine contains valuable nutrients including nitrogen, phosphorus, and potassium This study concerns the removal and recovery of ammonia from urine by stripping and absorption processes Throughout the experiments, ammonia was stripped with air in a batch system and absorbed in sulphuric acid solution Combined mass transfer coefficient (KL × a) for urine–air interaction, was calculated for different pH levels and air flow rates, by using a spherical stripping unit equipped with a ceramic fine-pore air stone (average pore size 40 microns) (KL × a) was observed to increase with increasing pH level and air flow rate The highest value of combined mass transfer coefficient was 048 h−1 , obtained at a pH of 12 and an air flow rate of 027 m3/h In the stripping process, a direct relationship was observed between air flow rate and mass transfer rate At an air flow rate of 021 m3/h, and at pH 12, the highest mass transfer rate (0085 g/h) was obtained In the absorption unit, aver

The role of soil properties in regulating non‐equilibrium macropore flow and solute transport in agricultural topsoils

Abstract: Summary Dual-permeability models can account for the strong influence of soil macropores on contaminant transport, but their predictive application is hampered by the difficulty in estimating a priori values for the rate coefficient controlling lateral mass exchange between the two flow domains. Our aim was to investigate the possibility of estimating the mass transfer coefficient in the dual-permeability model MACRO from fundamental soil properties. To this end, we calibrated MACRO against transient chloride leaching tests carried out on 33 undisturbed soil columns taken from the topsoils of three agricultural fields, characterized by a wide range of texture and organic matter content. The global search algorithm SUFI was used to derive optimum values of the mass transfer coefficient in each column. A Monte Carlo procedure was carried out on two columns to investigate the stability of the estimates in the presence of potential errors in fixed parameters. Despite such errors, c. 50% of the variation in mass transfer for this data set could be explained by two fundamental soil properties: the geometric mean particle size and the organic matter content. Soils of coarser texture and larger organic matter content were characterized by stronger lateral mass exchange and therefore weaker macropore flow. Harrowing and a 6-year grass ley also reduced the extent of non-equilibrium transport. Our results suggest that a robust functional description of the effects of soil structure on chemical transport is possible for predictive management applications of dual-permeability models across larger areas (i.e. mapping leaching risks at field, farm and catchment scales).

Mass Transfer of CO2 Into Water and Surfactant Solutions

Abstract: The mass transfer of CO2 into water and aqueous solutions of sodium dodecyl sulphate (SDS) is experimentally studied using a pressure, volume, temperature (PVT) cell at different initial pressures and a constant temperature (T = 25°C). It is observed that the transfer rate is initially much larger than expected from a diffusion process alone. The model equations describing the experiments are based on Fick's Law and Henry's Law. The experiments are interpreted in terms of two effective diffusion coefficients—one for the early-stages of the experiments and the other one for the later stages. The results show that at the early stages, the effective diffusion coefficients are one order of magnitude larger than the molecular diffusivity of CO2 in water. Nevertheless, in the later stages the extracted diffusion coefficients are close to literature values. It is asserted that at the early stages, density-driven natural convection enhances the mass transfer. A similar mass transfer enhancement was obser...

Supercritical fluid extraction of chamomile flower heads: Comparison with conventional extraction, kinetics and scale-up

Abstract: Supercritical fluid extraction of chamomile flower heads was performed on semi continuous extraction apparatus in the lab scale using carbon dioxide as solvent. The results of high pressure experiments were compared with those obtained with Soxhlet extraction, steam distillation and maceration. The obtained extracts were analysed by HPLC on α-bisabolol, matricine and chamazulene content and by gravimetrical method on essential oil and waxes content. The highest content of active components in extracts and highest extraction yield were obtained using SFE at 250 bar and 40 °C. At this extraction conditions the two step separation was used to optimize the separation of essential oil from unwanted components. Dynamic behaviour of the SFE with single step separation runs were analysed using two mathematical models for describing the constant rate period and subsequent falling rate period. Based on the experimental data, external mass transfer coefficient, diffusion coefficient and diffusivity in solid phase were estimated. Results showed acceptable agreement of calculated and experimental data. Based on the parameters determined in the lab scale the extraction process was successfully transferred to pilot scale.

Circulation liquid velocity, gas holdup and volumetric oxygen transfer coefficient in external-loop airlift reactors

Abstract: The effects of the horizontal connection length (0.1≤L c ≤0.5 m), the cross-sectional area ratio of downcomer-to-riser (0.11≤A d /A r ≤0.53), and the superficial gas velocity on gas phase holdups in the riser and downcomer were studied. The circulation liquid velocity, the mixing performance and the volumetric mass transfer coefficient in the external-loop airlift reactors were also measured. The horizontal connection length and A d /A r were major parameters which strongly affected the performance of external-loop airlift reactors. Useful correlations in the external-loop airlift reactors were obtained for gas holdups, the volumetric mass transfer coefficient, the circulation liquid velocity, and the mixing time

Modeling of oxygen mass transfer in a gas–liquid airlift reactor

Abstract: This article focuses on the physical modeling and numerical simulation of mass transfer in two-phase bubbly flow in an airlift internal loop reactor. The objective of this article is to show the ability of computational fluid dynamics (CFD) to correctly simulate mass transfer in such a bubbly reactor. The modeling of two-phase bubbly flow is based on the socalled two-fluid model derived from Reynolds-averaged Navier–Stokes equations in twophase flow. From the hydrodynamic perspective, the flow is steady state. Given the steadystate distributions of phases, interfacial area, and velocity field in the whole volume of the airlift, mass transfer is computed and the evolution of oxygen concentration in the two phases is predicted. Numerical simulations are discussed after comparison to experimental data. The simulations are validated in terms of oxygen concentration in the liquid vs. time. Then, different points are discussed, in particular, the perfectly mixed reactor assumption in the liquid phase and the spatial and temporal heterogeneity of oxygen concentration in the gas arising from oxygen impoverishment in bubbles in the downcomer. This leads to heterogeneity of the transfer driving force between the gas and the liquid. Bubble age or residence time in the airlift loop reactor has been calculated to show the weak renewal of oxygen in bubbles in the downcomer. This discussion generates questions on the estimation of a global mass transfer coefficient from experiments in such a heterogeneous airlift reactor. 2007 American Institute of Chemical Engineers AIChE J, 53: 316–326, 2007

Sulfur Dioxide Absorption in a Bubbling Reactor with Suspensions of Bayer Red Mud

Abstract: In this work, we studied the SO2 absorption with suspensions of Bayer red mud (the solid residue of the Bayer process for alumina production from bauxite) using a laboratory-scale bubbling reactor with continuous feed of both gas and liquid phases A few preliminary tests were carried out in order to calculate the physical mass transfer coefficients in both the gas and liquid sides Then, the ability of red mud suspensions for sulfur dioxide absorption was studied at several different flow rates of both the liquid and gas streams The absorption rate was measured for four different suspension concentrations The absorption phenomena were modeled using the film theory and assuming two different fluid dynamics for the gas phase The liquid-side mass transfer coefficient and the enhancement factor for chemical absorption were calculated from the experimental results using the model