The reaction engineering of electrochemical cells—II. Packed bed electrodes with orthogonal flow of current and solution

The analogy with an endothermic chemical reaction in a plug-flow non-isothermal reactor has been extended to the case of a packed bed electrode with orthogonal flow of current and solution (flow-by electrode). Comparison of the predicted (macrokinetic) polarisation curves with experimental ones obtained for equimolar ferri/ferrocyanide in alkaline solution in reticulated metal foam electrodes is satisfactory. Information on the microkinetics within the electrode is given implicitly. The sensitivity of the calculation to operating parameters is also discussed.     

An approximate economic evaluation of three-dimensional chemically modified electrodes

A mathematical analogue based on an array of transmission lines has been used to predict the performance of chemically modified three-dimensional electrodes under typical conditions. Even for reactions with low exchange currents, considerable non-uniformity of activation is predicted in the direction of current flow so that the electrode cannot be scaled-up indefinitely in this direction without penalty. At the same time the conversion per pass of the electrode is so low that it can be considered to be a constant concentration system. An approximate economic forecast based on the results of the model suggests production costs of the order of $500 to $5000 kg^–1 for a product of molecular weight 200, depending on the thickness of the electrode and the maximum permissible overvoltage. Installed capital costs are estimated to total about $ 100000 for a capacity of 20 to 170 kg^–1 y^–1) also depending on the maximum permissible overvoltage.     

Laminar radial flow electrochemical reactors. I. Flow fields

The velocity fields of three laminar radial flow electrochemical reactors are modeled using numerical and semi-analytical techniques. The capillary gap cell configuration is modeled using Galerkin finite element (GFEM) analysis and the asymptotic form of its velocities presented. An approximate asymptotic expression for entry length is also derived and compared to predicted entry lengths from the GFEM. Qualitative agreement is achieved. Two areas of flow separation are observed, their location being a function of gap width, flow Reynolds number (Re) and inlet pipe diameter. The rotating electrolyzer (REL) flow field is also simulated with the GFEM model. The insensitivity of the REL radial velocity profiles as a function of flow rate is shown. The shape of the radial velocity profiles and the degree of separation of the radial velocity jets are shown to be determined by the Taylor number (being the ratio of half-gap width over the theoretical boundary layer thickness). The asymptotic entry length solution is shown to provide a better estimate for this cell than for the capillary gap cell. Unlike the previous cells the pump cell shows less asymptotic behavior and is therefore more difficult to simulate. The GFEM approach is usually too costly for this cell and therefore perturbation techniques are applied. The resulting semi-analytical solution adequately represents laminar pump cell velocity profiles over a broad range of parameter values and is very short and easy to implement. One high Taylor number simulation is performed using the GFEM and the previously reported decoupling of electrodic mass transfer is interpreted via velocity profiles.Nomenclature a gap width - Q volumetric flow rate (m³ s^–1) - r dimensionless radius - R radius (m) - Re Reynolds number (v _c a/v) - Re _gap gap Reynolds number (a ²/v) - Re rotational Reynolds number (R ₀ ² /v) - Sc Schmidt number (v/D) - spin dimensionless group (Equation 8) - t time (s) - v _c characteristic velocity (m s^–1) two defined: for FEM analysis it wasQ/b ² for Perturbation analysis 6Q/(2R _in a) - v _r dimensionless radial velocity - v _z dimensionless axial velocity - v dimensionless azimuthal velocity - V velocity (m s^–1) - z dimensionless axial distance Greek symbols Taylor number (Equation 7) - ratio of characteristic lengths (a/R _o ) - viscosity (kg m^–1 s) - constant - density (kg m^–3) - azimuthal direction - kinematic viscosity (m² s^–1) - angular velocity (rad s^–1)     

Production of active manganese dioxide in an electrochemical pump cell

Active manganese dioxide has been produced in an electrochemical pump cell by the oxidation of manganese sulphate in sulphuric acid and the production rate and current efficiency have been related to the transport of the intermediate (Mn³⁺) ions. Space-time yields of 87–96 mol h^?1 m^?2 have been obtained, with current efficiencies of 93–86%, depending on current density. It is shown that an energy consumption of about 4 kWh kg^?1 can be achieved with continuous production of active MnO₂.     

Electrochemical reaction engineering

Some typical designs of electrochemical cell are reviewed in terms of chemical reaction engineering and factors which influence the selectivity of electrosynthetic reactions are discussed.     

Graph and model transformation tools for model migration

We describe the results of the Transformation Tool Contest 2010 workshop, in which nine graph and model transformation tools were compared for specifying model migration. The model migration problem—migration of UML activity diagrams from version 1.4 to version 2.2—is non-trivial and practically relevant. The solutions have been compared with respect to several criteria: correctness, conciseness, understandability, appropriateness, maturity and support for extensions to the core migration task. We describe in detail the comparison method, and discuss the strengths and weaknesses of the solutions with a special focus on the differences between graph and model transformation for model migration. The comparison results demonstrate tool and language features that strongly impact the efficacy of solutions, such as support for retyping of model elements. The results are used to motivate an agenda for future model migration research (including suggestions for areas in which the tools need to be further improved).     

A model identification scheme for driver-following dynamics in road traffic

The driver-following, or car-following, model is one of the most fundamental driver behavior models that are applied in intelligent transport applications. Its fidelity determines the applicability of microscopic traffic simulators, where the model is often implemented to mimic real traffic. Meanwhile, the behavioral model is fundamental to the development of advanced driving assistance systems (ADAS). This paper develops a dynamic model identification approach based on iterative usage of the extended Kalman Filtering (EKF) algorithm. Among other things, this allows to carry out model identification using a rather general optimization objective on the whole physical states of the following vehicle. In particular, the method is established on the basis of the equivalence between the Kalman filter and the recursive least squares (RLS) method in a specific context of parameter identification. To illustrate the method, two car-following models are studied in numerical experiments using real car-following data. The method has shown advantages in replication and prediction of vehicle dynamics in car-following over the conventional approaches. It has also the potential to be further extended for building tactical driving controllers in intelligent transportation applications.     

Degree-Constrained Graph Orientation: Maximum Satisfaction and Minimum Violation

A degree-constrained graph orientation of an undirected graph G is an assignment of a direction to each edge in G such that the outdegree of every vertex in the resulting directed graph satisfies a specified lower and/or upper bound. Such graph orientations have been studied for a long time and various characterizations of their existence are known. In this paper, we consider four related optimization problems introduced in reference (Asahiro et al. LNCS 7422, 332–343 (2012)): For any fixed non-negative integer W, the problems MAX W-LIGHT, MIN W-LIGHT, MAX W-HEAVY, and MIN W-HEAVY take as input an undirected graph G and ask for an orientation of G that maximizes or minimizes the number of vertices with outdegree at most W or at least W. As shown in Asahiro et al. LNCS 7422, 332–343 (2012)).     

Thermodynamic calculations made easy

Thermodynamic calculations are used regularly by researchers at universities and in industry to reduce experimental work and to know the equilibrium state. The use of fast computers has supported the development of general software and databases. These fast computers have reached a mature state where almost any type of equilibrium or diagram can be calculated readily. However, the use of such general software, even if it is called “user friendly,” is too difficult except for specialists. There is a need for simplification. The new type of user interface is called an “engineering-oriented” user interface. Ideas for such an interface are discussed. It is based on the most modern hardware and software technology using UNIX and X-windows on modern workstations. This paper was presented at the International Phase Diagram Prediction Symposium sponsored by the ASM/MSD Thermodynamics and Phase Equilibria Committee at Materials Week, October 21 -23,1991, in Cincinnati, Ohio. The symposium was organized by John Morral, University of Connecticut, and Philip Nash, Illinois Institute of Technology.