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Articles 211 - 240 of 247

Full-Text Articles in Chemical Engineering

A Comparison Of Newman's Numerical Technique And Deboor's Algorithm, D. A. Curtis, T. I. Evans, Ralph E. White Jan 1989

A Comparison Of Newman's Numerical Technique And Deboor's Algorithm, D. A. Curtis, T. I. Evans, Ralph E. White

Faculty Publications

No abstract provided.

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Estimation Of Electrode Kinetic Parameters Of The Lithium/Thionyl Chloride Cell Using A Mathematical Model, T. I. Evans, Ralph E. White Jan 1989

Estimation Of Electrode Kinetic Parameters Of The Lithium/Thionyl Chloride Cell Using A Mathematical Model, T. I. Evans, Ralph E. White

Faculty Publications

A one-dimensional mathematical model for the lithium/thionyl chloride primary cell is used in conjunction with a parameter estimation technique, in order to estimate the electrode kinetic parameters of this electrochemical system. The electrode kinetic parameters include the anodic transfer coefficient and exchange current density of the lithium oxidation, a,1 and i0,1,ref; the cathodic transfer coefficient and the effective exchange current density of the thionyl chloride reduction, c,4 and a0i0,4,ref, and a morphology parameter, . The parameter estimation is performed on simulated data first in order to gain confidence in the method. Data reported in …

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A Mathematical Model Of A Lithium/Thionyl Chloride Primary Cell, T. I. Evans, T. V. Nguyen, Ralph E. White Jan 1989

A Mathematical Model Of A Lithium/Thionyl Chloride Primary Cell, T. I. Evans, T. V. Nguyen, Ralph E. White

Faculty Publications

A one-dimensional mathematical model for the lithium/thionyl chloride primary cell has been developed to investigate methods of improving its performance and safety. The model includes many of the components of a typical lithium/thionyl chloride cell such as the porous lithium chloride film which forms on the lithium anode surface. The governing equations are formulated from fundamental conservation laws using porous electrode theory and concentrated solution theory. The model is used to predict one-dimensional, time dependent profiles of concentration, porosity, current, and potentialas well as cell temperature and voltage. When a certain discharge rate is required, the model can be used …

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A Thermal Analysis Of A Spirally Wound Battery Using A Simple Mathematical Model, T. I. Evans, Ralph E. White Jan 1989

A Thermal Analysis Of A Spirally Wound Battery Using A Simple Mathematical Model, T. I. Evans, Ralph E. White

Faculty Publications

A two-dimensional thermal model for spirally wound batteries has been developed. The governing equation of the model is the energy balance. Convective and insulated boundary conditions are used, and the equations are solved using a finite element code called TOPAZ2D. The finite element mesh is generated using a preprocessor to TOPAZ2D called MAZE. The model is used to estimate temperature profiles within a spirally wound D-size cell. The model is applied to the lithium/thionyl chloride cell because of the thermal management problems that this cell exhibits. Simplified one-dimensional models are presented that can be used to predict best and worst …

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Electrochemical Production And Corrosion Testing Of Amorphous Ni-P, Jose L. Carbajal, Ralph E. White Jan 1988

Electrochemical Production And Corrosion Testing Of Amorphous Ni-P, Jose L. Carbajal, Ralph E. White

Faculty Publications

Ni-P alloys were prepared by electrodeposition under different conditions on a rotating disk electrode. A variety of alloys were prepared ranging from Ni-15P to Ni-25P. An indirect reduction of species in solution involving several steps appears to be favored over the direct reduction at the electrode based on the low P content in the alloy. Energy dispersion x-ray microanalysis was used to determine composition of the alloy. Transmission electron microscopy and x-ray diffraction corroborated the amorphous nature of the structure. The physical and chemical homogeneity of the metallic glasses produced electrochemically is substantiated by the absence of electrochemical localized attack. …

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A Two-Dimensional Mathematical Model Of A Porous Lead Dioxide Electrode In A Lead-Acid Cell, E. C. Dimpault-Darcy, T. V. Nguyen, Ralph E. White Jan 1988

A Two-Dimensional Mathematical Model Of A Porous Lead Dioxide Electrode In A Lead-Acid Cell, E. C. Dimpault-Darcy, T. V. Nguyen, Ralph E. White

Faculty Publications

A two-dimensional mathematical model is presented for a lead dioxide electrode in a lead-acid cell. It is used to simulate the time dependent behavior of the electrode during discharge. The model contains six dependent variables: the concentration of the acid electrolyte, the porosity, the electrical potentials of the solid and solution phases, and the two directional components of the current density in the electrolyte. The effect of the electrode grid was included by varying the conductivity of the solid. Parameters such as electrode conductivity, electrode dimensions, and temperature are investigated to understand their effects on electrode discharge performance.

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Secondary Current Distributions Using Topaz2d And Linear Kinetics, E. C. Dimpault-Darcy, Ralph E. White Jan 1988

Secondary Current Distributions Using Topaz2d And Linear Kinetics, E. C. Dimpault-Darcy, Ralph E. White

Faculty Publications

Secondary current density distributions are of interest
to cell designers. The purpose of this note is to illustrate
how to use an existing numerical method to determine
these distributions for cells that contain conducting and
nonconducting bodies between the main anode and cathode.

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Analysis Of Electrokinetic Data By Parameter Estimation And Model Discrimination Techniques, Prosper K. Adanuvor, Ralph E. White Jan 1988

Analysis Of Electrokinetic Data By Parameter Estimation And Model Discrimination Techniques, Prosper K. Adanuvor, Ralph E. White

Faculty Publications

An alternative approach to classical methods of electrochemical data analysis is presented. This alternative method is based on nonlinear parameter estimation and model discrimination techniques. The method is used to obtain the relevant kinetic and transport parameters and to elucidate the kinetic mechanism of O2 reduction at carbon and silver electrodes in alkaline electrolytes.

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A Mathematical Model For Predicting Cyclic Voltammograms Of Electronically Conductive Polypyrrole, Taewhan Yeu, Trung V. Nguyen, Ralph E. White Jan 1988

A Mathematical Model For Predicting Cyclic Voltammograms Of Electronically Conductive Polypyrrole, Taewhan Yeu, Trung V. Nguyen, Ralph E. White

Faculty Publications

Polypyrrole is an attractive polymer for use as a high energy density secondary battery because of its potential as an inexpensive, lightweight, and noncorrosive electrode material. A mathematical model to simulate cyclic voltammograms for polypyrrole is presented here. The model is for a conductive porous electrode film on a rotating disk electrode (RDE) and is used to predict the spatial and time dependence of concentration, overpotential, and stored charge profiles within a polypyrrole film. The model includes both faradaic and capacitive charge components in the total current density expression.

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Predicting Shunt Currents In Stacks Of Bipolar Plate Cells With Conducting Manifolds, H. S. Burney, Ralph E. White Jan 1988

Predicting Shunt Currents In Stacks Of Bipolar Plate Cells With Conducting Manifolds, H. S. Burney, Ralph E. White

Faculty Publications

A method is presented for predicting shunt currents in stacks of bipolar plate cells with conducting manifolds. The method is based on the requirement that the potential drop through the solution in a manifold be large enough to force current to leave the solution and to enter the conducting manifold. The current that leaves the solution in the manifold enters the conducting manifold at the anode end of the stack and returns to the solution at the cathode end. This could cause catastrophic failure of a manifold.

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Oxygen Reduction On Silver In 6.5m Caustic Soda Solution, Prosper K. Adanuvor, Ralph E. White Jan 1988

Oxygen Reduction On Silver In 6.5m Caustic Soda Solution, Prosper K. Adanuvor, Ralph E. White

Faculty Publications

The cathodic reduction of oxygen in 6.5M membrane-grade caustic soda solution has been studied experimentally at a silver rotating disk electrode at 25°C. The results can be approximated by the parallel mechanism for oxygen reduction with catalytic decomposition of peroxide. Further analysis of this mechanism indicates that the sequential process with catalytic decomposition of peroxide predominates over the direct 4e– process. Direct application of the sequential mechanism to the data indicates that the latter mechanism with catalytic decomposition of peroxide much more accurately reflects the experimental results. The relevant kinetic parameters are calculated on the basis of …

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A Mathematical Model For The Electrodeposition Of Alloys On A Rotating Disk Electrode, Shiuan Chen, Ken-Ming Yin, Ralph E. White Jan 1988

A Mathematical Model For The Electrodeposition Of Alloys On A Rotating Disk Electrode, Shiuan Chen, Ken-Ming Yin, Ralph E. White

Faculty Publications

A general multiple electrode reaction model for electrodeposition of alloys on a rotating disk electrode is presented. Included in the model are mass transport equations with the effect of ionic migration, Butler-Volmer kinetic rate expressions, and the mole fractions of the individual components in the solid state. The model shows that the effect of ionic migration is important and that plating variables such as applied potential, pH, and bulk concentration can be included. Two examples (Ni-P and Ru-Ni-P) are used to illustrate the predictions of the model.

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Electrodeposition Of Copper-Nickel Alloys From Citrate Solutions On A Rotating Disk Electrode, Ramona Y. Ying, Patrick K. Ng, Z. Mao, Ralph E. White Jan 1988

Electrodeposition Of Copper-Nickel Alloys From Citrate Solutions On A Rotating Disk Electrode, Ramona Y. Ying, Patrick K. Ng, Z. Mao, Ralph E. White

Faculty Publications

A mathematical model is developed to simulate the electrodeposition of Cu-Ni alloy from citrate solutions onto a rotating disk electrode under potentiostatic control. The model includes the influence of diffusion, ionic migration, forced convection, and homogeneous equilibria. The three major electrochemical reactions treated in the model are copper deposition, nickel deposition, and hydrogen evolution. Using experimental parameters when available, the model was fitted and tested against experimentally-obtained results for different bath compositions and operating conditions. The model agreed reasonably well with the experimental results particularly in the codeposition region, –1.0 to –1.2V vs. SCE, where hydrogen evolution is not the …

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A Mathematical Model For The Initial Corrosion Rate Of A Porous Layer On A Rotating Disk Electrode, William E. Ryan, Ralph E. White, S. L. Kelly Jan 1987

A Mathematical Model For The Initial Corrosion Rate Of A Porous Layer On A Rotating Disk Electrode, William E. Ryan, Ralph E. White, S. L. Kelly

Faculty Publications

A mathematical model is presented for the initial corrosion rate of a porous layer on a rotating disk electrode. The model is used to predict the corrosion potential and corrosion current density for a porous electrode made of pure iron in aerated caustic solutions. The dependence of these predictions on some of the properties of the porous layer is presented. It is shown that the corrosion rate depends significantly on the specific surface area of the porous electrode.

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The Effect Of The Tribromide Complex Reaction On The Oxidation/Reduction Current Of The Br2/Br– Electrode, P K. Adanuvor, Ralph E. White, S. E. Lorimer Jan 1987

The Effect Of The Tribromide Complex Reaction On The Oxidation/Reduction Current Of The Br2/Br– Electrode, P K. Adanuvor, Ralph E. White, S. E. Lorimer

Faculty Publications

The Br2/Br– electrode reaction with tribromide complex formation reaction in the solution, a chemical-electrochemical (C-E) type reaction, has been investigated in order to determine the effect of the chemical reaction on the electrode kinetics. It is shown that the chemical reaction has little effect on the electrode kinetics at very slow homogeneous reaction rates, but has a more drastic effect on the electrode kinetics at faster homogeneous reaction rates. Also, the kinetics at the electrode are affected by changes in the concentrations of the active species (Br2, Br–, and Br3–) …

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Modeling The Rotating Disk Electrode For Studying The Kinetics Of Electrochemical Reactions, P K. Adanuvor, Ralph E. White, S E. Lorimer Jan 1987

Modeling The Rotating Disk Electrode For Studying The Kinetics Of Electrochemical Reactions, P K. Adanuvor, Ralph E. White, S E. Lorimer

Faculty Publications

A general mathematical model for studying the kinetics of electrochemical reactions at a rotating disk electrode under steady-state potentiostatic conditions is presented. The model, apart from predicting the net and partial current densities at given values of the applied potential, the ohmic potential drop, and the concentration and potential profiles in the solution, also accounts for homogeneous reactions of any order in the solution and noncharge transfer reactions at the electrode surface. The versatility of the model is demonstrated by the application of the model to a variety of complex reaction schemes.

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A Mathematical Model Of A Zinc/Bromine Flow Cell, T. I. Evans, Ralph E. White Jan 1987

A Mathematical Model Of A Zinc/Bromine Flow Cell, T. I. Evans, Ralph E. White

Faculty Publications

A mathematical model is presented for a zinc/bromine flow cell. The model includes a thin porous layer on the bromine electrode and a porous separator. The independent parameters of the porous layer are defined, and their effect on cell performance during charge and discharge is investigated. The dependence of the round trip energy efficiency on the thickness of the porous layer and mode of discharge is presented. The predictions of the model show that a maximum round trip energy efficiency of 70% should be possible under the design conditions considered.

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Simulation Of The Polarization Curves For Oxygen Reduction At A Rotating Disk Electrode, P. K. Adanuvor, Ralph E. White Jan 1987

Simulation Of The Polarization Curves For Oxygen Reduction At A Rotating Disk Electrode, P. K. Adanuvor, Ralph E. White

Faculty Publications

The electrochemical reduction of oxygen in 1M NaOH solution is simulated at a rotating disk electrode. Steady-state polarization curves are presented for possible reaction schemes for the reduction process. The effect of changes in the kinetic parameters on the polarization curves is demonstrated and special attention is focused on the production of hydrogen peroxide.

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Utility Of An Empirical Method Of Modeling Combined Zero Gap/Attached Electrode Membrane Chlor-Alkali Cells, Clifford W. Walton, Ralph E. White Jan 1987

Utility Of An Empirical Method Of Modeling Combined Zero Gap/Attached Electrode Membrane Chlor-Alkali Cells, Clifford W. Walton, Ralph E. White

Faculty Publications

An extensive survey of the Docktor-Ingenieur Dissertationen of Jakob Jörissen and Klaus-R. Menschig, both originally from the Universität Dortmund, is presented in regard to the empirical modeling of membrane chlor-alkali cells and how it can be applied to a combined zero gap/attached porous electrode layer membrane cell. Particular emphasis isplaced on Menschig's work on zero gap (ZG) and attached porous electrode layer (APEL) membrane chlor-alkali cells, the first such research to appear in the open literature. Menschig developed various computer programs to characterize these ZG and APEL membrane chlor-alkali cells. He characterized these cells by using the following parameters: the …

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A Review Of Mathematical Modeling Of The Zinc/Bromine Flow Cell And Battery, T. I. Evans, Ralph E. White Jan 1987

A Review Of Mathematical Modeling Of The Zinc/Bromine Flow Cell And Battery, T. I. Evans, Ralph E. White

Faculty Publications

Mathematical models which have been developed to study various aspects of the zinc/bromine cell and stack of cells are reviewed. Development of these macroscopic models begins with a material balance, a transport equation which includes a migration term for charged species in an electric field, and an electrode kinetic expression. Various types of models are discussed: partial differential equation models that can be used to predict current and potential distributions, an algebraic model that includes shunt currents and associated energy losses and can be used to determine the optimum resistivity of an electrolyte, and ordinary differential equation models that can …

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A Mathematical Model Of A Lead-Acid Cell: Discharge, Rest, And Charge, Hiram Gu, T. V. Nguyen, Ralph E. White Jan 1987

A Mathematical Model Of A Lead-Acid Cell: Discharge, Rest, And Charge, Hiram Gu, T. V. Nguyen, Ralph E. White

Faculty Publications

A mathematical model of a lead-acid cell is presented which includes the modeling of porous electrodes and various physical phenomena in detail. The model is used to study the dynamic behavior of the acid concentration, the porosity of the electrodes, and the state of charge of the cell during discharge, rest, and charge. The dependence of the performance of the cell on electrode thicknesses and operating temperature is also investigated.

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Predicting Shunt Currents In Stacks Of Bipolar Plate Cells, Ralph E. White, C. W. Walton, H. S. Burney, R. N. Beaver Jan 1986

Predicting Shunt Currents In Stacks Of Bipolar Plate Cells, Ralph E. White, C. W. Walton, H. S. Burney, R. N. Beaver

Faculty Publications

A method is presented for predicting shunt currents in stacks of undivided and divided bipolar plate cells. The method is an efficient way of solving the coupled sets of algebraic equations that arise from using circuit analog models to represent the current paths in stacks of undivided or divided bipolar plate cells. These algebraic equations can be eitherlinear or nonlinear depending upon the current-potential relationships used in the model (i.e., nonlinear circuit elements can be included). The method is used to show the importance of including nonsymmetrical resistances and nonlinear circuit elements in the models. Also, the method …

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A Mathematical Model Of A Zn/Br2 Cell On Charge, M J. Mader, Ralph E. White Jan 1986

A Mathematical Model Of A Zn/Br2 Cell On Charge, M J. Mader, Ralph E. White

Faculty Publications

A mathematical model of a parallel plate electrochemical cell with a separator and a homogeneous bulk reaction is presented. The model is based on the Zn/Br2 redox couple and can be used as an aid for the design of an efficient rechargeable storage battery. It is shown that four independent variables exist for the system at a fixed temperature: the effective separator thickness, the residence time, the channel width, and the potential driving force. Performance criteria of interest for the Zn/Br2 battery are defined. Predictions of performance during the charging process are presented. It is shown that the …

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Parallel-Plate Electrochemical Reactor Model: A Method For Determining The Time-Dependent Behavior And The Effects Of Axial Diffusion And Axial Migration, T. V. Nguyen, C. W. Walton, Ralph E. White, J. Van Zee Jan 1986

Parallel-Plate Electrochemical Reactor Model: A Method For Determining The Time-Dependent Behavior And The Effects Of Axial Diffusion And Axial Migration, T. V. Nguyen, C. W. Walton, Ralph E. White, J. Van Zee

Faculty Publications

A method is presented for determining the effects of time dependence, axial diffusion, and axial migration in aparallel-plate electrochemical reactor (PPER). The method consists of formulating the governing equations and applying a numerical integration technique to solve a set of time-dependent, nonlinear, coupled, multidimensional equations. This formulation reveals that the steady-state performance of the PPER depends on the cell potential and three dimensionless groups. Predictions of the concentration, potential, and local current distributions in a PPER are presented for the electrowinning of copper from an aqueous, hydrochloric acid solution. These predictions show that axial diffusion and axial migration are significant …

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Simple Models For Diaphragm-Type Chlorine/Caustic Cells Ii. Effect Of Acidic Anolyte On Steady-State Caustic Yield, John Van Zee, Ralph E. White Jan 1986

Simple Models For Diaphragm-Type Chlorine/Caustic Cells Ii. Effect Of Acidic Anolyte On Steady-State Caustic Yield, John Van Zee, Ralph E. White

Faculty Publications

A simple steady-state model of a diaphragm-type chlorine/caustic cell in which the diaphragm is divided into two regions by a homogeneous acid-base reaction is presented. The location of the reaction affects significantly the caustic yield and effluent concentration. The model is used to predict the location of this reaction as a function of the operating variables, the physical constants, and three measurable properties of the diaphragm. These measurable properties are the MacMullin number or resistivity ratio of electrolyte-filled diaphragm relative to the electrolyte, the Darcy's law diaphragmpermeability, and the diaphragm thickness. The model is used to predict a maximum in …

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Simple Models For Diaphragm-Type Chlorine/Caustic Cells I. Dynamic Behavior, John Van Zee, Ralph E. White, A T. Watson Jan 1986

Simple Models For Diaphragm-Type Chlorine/Caustic Cells I. Dynamic Behavior, John Van Zee, Ralph E. White, A T. Watson

Faculty Publications

A simple model of the dynamic behavior of a diaphragm-type chlorine/caustic cell is presented. The model is based upon measurable diaphragm properties and the mass transfer of hydroxyl ion through the diaphragm. The anolyte is modeled simply as a region in which the OH– ion concentration is fixed, the diaphragm is modeled as a plug-flow reactor with an electrochemical reaction occurring at the catholyte/diaphragm interface where the cathode is placed, and the catholyte is modeled as a completely stirred flow reactor. Analytical integration of the governing equations for thesemodels yields two mathematical expressions: one for the concentration distribution of …

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Parallel Plate Electrochemical Reactor Model: Material Balance Closure And A Simplification, M J. Mader, C W. Walton, Ralph E. White Jan 1986

Parallel Plate Electrochemical Reactor Model: Material Balance Closure And A Simplification, M J. Mader, C W. Walton, Ralph E. White

Faculty Publications

A material balance closure calculation is presented to test the consistency of a previously published model of a parallelplate electrochemical reactor. New expressions are used in this procedure to calculate the average concentration of species i and the average current density for reaction j from the predicted concentration and potential distributions. Also, the previously presented model equations are simplified by assuming that the axial concentration gradient for species i can be approximated by a step change from the known feed concentration to the unknown outlet concentration. This one-step model provides a qualitative evaluation of cell performance and adds insight into …

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A Mathematical Model For A Parallel Plate Electrochemical Reactor, Cstr, And Associated Recirculation System, T V. Nguyen, C W. Walton, Ralph E. White Jan 1986

A Mathematical Model For A Parallel Plate Electrochemical Reactor, Cstr, And Associated Recirculation System, T V. Nguyen, C W. Walton, Ralph E. White

Faculty Publications

A mathematical model is presented for a system comprised of a parallel plate electrochemical reactor (PPER) and a continuous, stirred-tank reactor (CSTR) under both total and partial recycle. The model is used to predict the time dependent behavior of the electrowinning of copper from an aqueous, hydrochloric acid solution. The model includes many important aspects of a PPER/CSTR system which have been neglected previously. These aspects are the kinetics of electrode reactions, the electroneutrality condition, three mass transfer processes for ionic species in the electrolyte (diffusion, ionic migration, and convection) and the electrode gap in the PPER, and the inclusion …

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Using Parameter Estimation Techniques With A Simple Model Of A Diaphragm-Type Electrolyzer To Predict The Electrical Energy Cost For Naoh Production, John Van Zee, Ralph E. White Jan 1985

Using Parameter Estimation Techniques With A Simple Model Of A Diaphragm-Type Electrolyzer To Predict The Electrical Energy Cost For Naoh Production, John Van Zee, Ralph E. White

Faculty Publications

Predictions of the electrical energy cost for NaOH production are determined as a function of the independent operating variables and diaphragm characterizing properties. The predictions are based on data from a statistically designed experiment, a simple model of a diaphragm-type electrolyzer, a simple model of the cell voltage losses, and parameter estimation techniques. The data were obtained over a sufficiently large range of operating conditions so that the resulting design equation may be industrially useful. The simple model of the diaphragm is based on the mass transport of the hydroxyl ion, a linear potential gradient, and is presented in terms …

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Extension Of Darby's Model Of A Hydrophylic Gas Fed Porous Electrode, Ralph E. White, M. A. Nicholson, L. G. Kleine, J. Van Zee, R. Darby Jan 1984

Extension Of Darby's Model Of A Hydrophylic Gas Fed Porous Electrode, Ralph E. White, M. A. Nicholson, L. G. Kleine, J. Van Zee, R. Darby

Faculty Publications

A model presented previously by one of the authors (1,2) is reviewed and extended. Aspects of this model which were not previously available in the open literature are considered, and the model is extended to include previously neglected terms in the governing differential equations, fractional reaction orders in the current density-overpotential expression, and mass-transfer coefficients to account for mass-transfer resistance of the reactants to the faces of the porous electrode. The model is used to predict quantities of interest for oxygen reduction in an acidic aqueous solution in a porous carbon electrode.

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