A transient computational fluid dynamic study of a laboratory-sclale fluorine electrolysis cell

Fluorine gas is produced industrially by electrolysing hydrogen fluoride in a potassium acid fluoride electrolyte. Fluorine is produced at the carbon anode, while hydrogen is produced at the mild-steel cathode. The fluorine produced has a wide range of uses, most notably in the nuclear industry where it is used to separate 235U and 238U. The South African Nuclear Energy Corporation (Necsa) is a producer of fluorine and requested an investigation into the hydrodynamics of their electrolysis cells as part of a larger national initiative to beneficiate more of South Africa’s large fluorspar deposits. Due to the extremely corrosive and toxic environment inside a typical fluorine electrolysis reactor, the fluid dynamics in the reactor are not understood well enough. The harsh conditions make detailed experimental investigation of the reactors extremely dangerous. The objective of this project is to construct a model that can accurately predict the physical processes involved in the production of fluorine gas. The results of the simulation will be compared to experimental results from tests done on a lab-scale reactor. A good correlation between reality and the simulacrum would mean engineers and designers can interrogate the inner operation of said reactors safely, effortlessly and economically. This contribution reports a time-dependent simulation of a fluorine-producing electrolysis reactor. COMSOL Multiphysics was used as a tool to construct a two dimensional model where the charge-, heat-, mass- and momentum transfer were fully coupled in one transient simulation. COMSOL is a finite element analysis software package. It enables the user to specify the dimensions of his/her investigation and specify a set of partial differential equations, boundary conditions and starting values. These equations can be coupled to ensure that the complex interaction between the various physical phenomena can be taken into account - an absolute necessity in a model as complex as this one. Results produced include a set of time dependent graphics where the charge-, heat-, mass- and momentum transfer inside the reactor and their development can be visualized clearly. The average liquid velocity in the reactor was also simulated and it was found that this value stabilises after around 90 s. The results of each transfer module are also shown at 100 s, where it is assumed that the simulation has achieved a quasi-steady state. The reactor, on which the model is based, is currently under construction and will be operated under the same conditions as specified in the model. The reactor, constructed of stainless steel, has a transparent side window through which both electrodes can clearly be seen. Thus the bubble formation and flow in the reactor can be studied effectively. Temperature will be measured with a set of thermocouples imbedded in PTFE throughout the reactor. The electric field will similarly be measured using electric induction probes.Dissertation (MEng)--University of Pretoria, 2012.Chemical Engineeringunrestricte

Comsol Modelling of Uniform Corrosion of Used Nuclear Fuel Canisters

Uniform corrosion of copper can occur in spent nuclear fuel canisters placed in deep geological repositories (DGR). To estimate the minimum thickness for safe design of canisters, it is necessary to analyze the corrosion rate. Copper Corrosion Model (CCM) has been used to model the corrosion process taking into account processes including adsorption/desorption, precipitation/dissolution, oxidation, and parameters including oxygen concentration, chloride, moisture and associated rate constants. In this work, CCM has been incorporated in COMSOL and validated with CCM. Once validated, the COMSOL model was used to examine the sensitivity of various parameters with respect to copper corrosion. It was found that initial chloride concentration, adsorption/desorption of cupric ions are parameters that most effect copper corrosion. The developed model can be used to simulate the uniform corrosion process under DGR conditions with more complexity including variation in temperature, saturation and pressure, and aid in the design of copper canisters

Mathematical Modeling of Solid Oxide Fuel Cells

In this thesis, an integrated microstructural–electrochemical modeling framework for Solid Oxide Fuel Cells (SOFCs) is presented. At the microscale, the model numerically reconstructs the microstructure of the electrodes, which are random porous composite media wherein the electrochemical reactions occur. The effective properties of the electrodes are evaluated in the reconstructed microstructures and used, as input parameters, in physically–based electrochemical models, consisting of mass and charge balances written in continuum approach, which describe the transport and reaction phenomena at the mesoscale within the cell. Therefore, the strong coupling between microstructural characteristics and electrochemical processes can be conveniently taken into account by the integrated model. The presented modeling framework represents a tool to fulfill a from–powder–to–power approach: it is able to reproduce and predict the SOFC macroscopic response, such as the current–voltage relationship, knowing only the powder characteristics and the operating conditions, which are the same measurable and controllable parameters available in reality. As a consequence, empirical, fitted or adjustable parameters are not required, feature which makes the model fully predictive and widely applicable in a broad range of conditions and fuel cell configurations as an interpretative tool of experimental data and as a design tool to optimize the system performance

Advanced nickel-hydrogen cell configuration study

Three nickel hydrogen battery designs, individual pressure vessel (IPV), common pressure vessel (CPV), and a bipolar battery module were studied. Weight, system complexity and cost were compared for a satellite operating in a 6 hour, 5600 nautical mile orbit. The required energy storage is 52 kWh. A 25% improvement in specific energy is observed by employing a bipolar battery versus a battery comprised of hundreds of IPV's. Further weight benefits are realized by the development of light weight technologies in the bipolar design

The materials processing research base of the Materials Processing Center

The goals and activities of the center are discussed. The center activities encompass all engineering materials including metals, ceramics, polymers, electronic materials, composites, superconductors, and thin films. Processes include crystallization, solidification, nucleation, and polymer synthesis

Computation and verification of workpiece shape in electrochemical machining

This investigation was motivated by the need for accurate prediction of electrochemical machined surfaces relative to corresponding tool geometries for given sets of machining parameters. A mathematical model was formulated which simulates the electrochemical erosion achieved by primary current distribution under steady tool feed rate, but with correction for variable efficiency. The equations comprising the mathematical model were programmed for solution by a digital computer, using discrete steps and a quasi-steady approach. The model was not completely analytical; it utilised an empirical values for specific metal removal rates. The efficiency of machining with NaNO₃ electrolyte was estimated from experimental results of other investigators. To assess the validity of the model, drilling test runs were performed with tubular electrodes having two geometries at the leading edge of the tool. Work specimens were made out of EN58J stainless steel, both NaC1 and NaNO₃ electrolytes were used. The correlation between experimentally obtained drilled surfaces and the computer predicted surfaces were satisfactory, justifying the assumptions made during the development of the model and the numerical methods of the solution used. This investigation has provided a method which could be successfully employed to predict the electrochemically machined profiles relative to tool geometries. This undoubtedly helps the production engineer in achieving the desired tolerances of the finished component eliminating the high cost of trial and error techniques.This investigation was motivated by the need for accurate prediction of electrochemical machined surfaces relative to corresponding tool geometries for given sets of machining parameters. A mathematical model was formulated which simulates the electrochemical erosion achieved by primary current distribution under steady tool feed rate, but with correction for variable efficiency. The equations comprising the mathematical model were programmed for solution by a digital computer, using discrete steps and a quasi-steady approach. The model was not completely analytical; it utilised an empirical values for specific metal removal rates. The efficiency of machining with NaNO₃ electrolyte was estimated from experimental results of other investigators. To assess the validity of the model, drilling test runs were performed with tubular electrodes having two geometries at the leading edge of the tool. Work specimens were made out of EN58J stainless steel, both NaC1 and NaNO₃ electrolytes were used. The correlation between experimentally obtained drilled surfaces and the computer predicted surfaces were satisfactory, justifying the assumptions made during the development of the model and the numerical methods of the solution used. This investigation has provided a method which could be successfully employed to predict the electrochemically machined profiles relative to tool geometries. This undoubtedly helps the production engineer in achieving the desired tolerances of the finished component eliminating the high cost of trial and error techniques

Second Microgravity Fluid Physics Conference

The conference's purpose was to inform the fluid physics community of research opportunities in reduced-gravity fluid physics, present the status of the existing and planned reduced gravity fluid physics research programs, and inform participants of the upcoming NASA Research Announcement in this area. The plenary sessions provided an overview of the Microgravity Fluid Physics Program information on NASA's ground-based and space-based flight research facilities. An international forum offered participants an opportunity to hear from French, German, and Russian speakers about the microgravity research programs in their respective countries. Two keynote speakers provided broad technical overviews on multiphase flow and complex fluids research. Presenters briefed their peers on the scientific results of their ground-based and flight research. Fifty-eight of the sixty-two technical papers are included here

Frontiers in Ultra-Precision Machining

Ultra-precision machining is a multi-disciplinary research area that is an important branch of manufacturing technology. It targets achieving ultra-precision form or surface roughness accuracy, forming the backbone and support of today’s innovative technology industries in aerospace, semiconductors, optics, telecommunications, energy, etc. The increasing demand for components with ultra-precision accuracy has stimulated the development of ultra-precision machining technology in recent decades. Accordingly, this Special Issue includes reviews and regular research papers on the frontiers of ultra-precision machining and will serve as a platform for the communication of the latest development and innovations of ultra-precision machining technologies