Publications

Analysis of the data obtained by the electrochemical monitoring technique for diffusion of a gas through a membrane is considered. It is shown that combining a numerical method with a nonlinear parameter estimation technique provides a means to determine values for the diffusion coefficient and the solubility of the diffusing gas. It is shown that better accuracy can be obtained for the diffusion coefficient and solubility of this gas by using the method presented and all experimental data rather than only part of the data, as has often been done in the past.

A five-point finite-difrerence procedure is presented which can be used to solve partial differential equations involving time or time-like derivatives and two spatial conditions (i.e. parabolic partial differential equations). Fourth-order accuracy is obtained by approximating the time derivative by five-point central finite differences and solving the resulting system of equations implicitly. The 1- and 2-D diffusion equations are solved to illustrate the procedure. © 1990.

A simple model for a parallel plate, zinc/bromine flow cell and associated storage tanks is presented and used to make time-dependent predictions for various quantities in the system. The model is based on a previously published algebraic model of the cell at steady-state and time-dependent, first-order differential equations for the storage tanks. The Butler- Volmer equation is used for the electrochemical reactions, and the homogeneous reaction between bromine and bromide is included. The model predictions indicate that the charging operation of a zinc/bromine battery can be significantly im- proved by using a storage tank with a larger residence time for the bromine side of the system.

A galvanostatic pulse plating model is presented for the electrodeposition of an alloy on a rotating disk electrode. This model is used to simulate the electrodeposition of nickel/chrome alloys. The mass transport equations used in the model include the effects of diffusion, migration and convection; and the electrode kinetics are described by the Butler‐Volmer equation. It is predicted that the effect of ionic migration is significant and therefore should be included in models of pulse plating. Copyright © 1990 American Institute of Chemical Engineers

Summary Using dimensionles variables in the governing and boundary condition equations, the dimensionless option of TOPAZ3D can be used to predict current density distributions in electroplating systems. This was illustrated by determining the curent density distributions in a modified Hull Cell.

The underlying principles and structure of an easy-to-use solver for two-point boundary-value problems described by sets of nonlinear ordinary differential equations is presented. The solution approach is based on the finite difference approximations for the derivatives. The Newton-Raphson iterative scheme with analytical Jacobians is used for solving the resulting large-scale nonlinear set of algebraic equations. Part 1 of the paper presents an in-depth analysis of the general problem and the solution method which results in a split of the overall problem into two distinct parts, a pure mathematical analytical part, which does not depend on the chosen numerical solution method, and a numerical part, which implements all the details of the numerical procedure. The prototype implementation, presented in Part 2, is based on this separation. It makes use of different programs which are specialized for solving particular subproblems identified in the analysis. An algebraic manipulator is used to aid in generating the Jacobians analytically and a matrix-oriented environment is used to implement the numerical matrix operations. The resulting package requires only the essential information from the user, namely the model equations and the solution domain variables as well as initial guesses of the solution. The package is a prototype that can be used to solve second-order problems based on three-point polynomial approximations of the derivatives. © 1990.

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 potential as well as cell temperature and voltage. When a certain discharge rate is required, the model can be used to determine the design criteria and operating variables which yield high cell capacities. Model predictions can be used to establish operational and design limits within which the thermal runaway problem, inherent in these cells, can be avoided.