Papers by Andreas Melcher
In this work commercial 18650 lithium-ion cells with LiMn2O4, LiFePO4 and Li(Ni0.33Mn0.33Co0.33)O... more In this work commercial 18650 lithium-ion cells with LiMn2O4, LiFePO4 and Li(Ni0.33Mn0.33Co0.33)O2 cathodes were exposed to external heating in an Accelerating Rate Calorimeter (es-ARC, THT Company) to investigate the thermal behavior under abuse conditions. New procedures for measuring external and internal pressure change of cells were developed. The external pressure was measured utilizing a gas-tight cylinder inside the calorimeter chamber in order to detect venting of the cells. For internal pressure measurements, a pressure line connected to a pressure transducer was directly inserted into the cell. During the thermal runaway experiments, three stages (low rate, medium rate and high rate reaction) have been observed. Both pressure and temperature change indicated different stages of exothermic reactions, which produced gases or/and heat. The onset temperature of thermal runaway was estimated according to temperature and pressure changes. Moreover, the different activation ener...
Over the last decades, great progress has been made in developing models to describe and simulate... more Over the last decades, great progress has been made in developing models to describe and simulate the time-spatial evolution of microstructure in polycrystals. A major problem is to find suitable initial conditions to start such a simulation. One possibility to solve this problem is the usage of experimental data given by Electron Back Scattering Diffraction (EBSD) measurement. These technique provides the grain structure of a polycrystal in terms of Eulerian angles. In this work, we introduce a algorithm based on quaternions to describe the reconstruction of a polycrystal from the EBSD data in two and three space dimensions. We describe the EBSD measurement and the mathematical background in detail. From this we deduce the reconstruction algorithm and give some simulation results.
Microwave materials processing at the Karlsruhe Institute of Technology
The thermal behavior of Li-ion cells is an important safety issue and has to be known under varyi... more The thermal behavior of Li-ion cells is an important safety issue and has to be known under varying thermal conditions. The main objectives of this work is to gain a better understanding of the temperature increase within the cell considering different heat sources under specified working conditions. With respect to the governing physical parameters, the major aim is to find out under which thermal conditions a so called Thermal Runaway occurs. Therefore, a mathematical electrochemical-thermal model based on the Newman model has been extended with a simple combustion model from reaction kinetics including various types of heat sources assumed to be based on an Arrhenius law. This model was realized in COMSOL Multiphysics modeling software. First simulations were performed for a cylindrical 1860 cell with a LiCoO2-cathode to calculate the temperature increase under two various simple electric load profiles and to compute critical system parameters. It has been found that the critical...
Modeling and Simulation the Thermal Runaway Behavior of Cylindrical Li-Ion Cells—Computing of Critical Parameter
Energies, 2016
Communications in Partial Differential Equations, May 1, 2008
We prove a Hopf-bifurcation theorem for the vorticity formulation of the Navier-Stokes equations ... more We prove a Hopf-bifurcation theorem for the vorticity formulation of the Navier-Stokes equations in R 3 in case of spatially localized external forcing. The difficulties are due to essential spectrum up to the imaginary axis for all values of the bifurcation parameter which a priori no longer allows to reduce the problem to a finite dimensional one.
Simulation for microwave heating of catalysts for CO 2 reduction to CO
2012 Ieee Mtt S International Microwave Symposium Digest, Jun 1, 2012
ABSTRACT Using the reverse water gas shift reaction (RWGS) one can produce carbon monoxide from c... more ABSTRACT Using the reverse water gas shift reaction (RWGS) one can produce carbon monoxide from carbon dioxide with the help of a catalyst. As the reaction is endothermic external energy in form of heat has to be applied. In the project CO2RRECT (CO2-Reaction using Regenerative Energies and Catalytic Technologies) [1], one task is to construct an applicator where the heating of the catalysts for the reaction is done by microwaves at a frequency of 2.45 GHz. This paper describes the simulation of such an applicator.
A Hopf bifurcation theorem for the vorticity formulation of the Navier-Stokes equations in three space dimensions
ABSTRACT
A microwave applicator for high homogeneous high temperature heating of catalysts
2013 IEEE MTT-S International Microwave Symposium Digest (MTT), 2013
ABSTRACT Using microwave heating allows for a fast and efficient volumetric heating. For chemical... more ABSTRACT Using microwave heating allows for a fast and efficient volumetric heating. For chemical reactors microwaves permit to generate the heat inside the catalyst bed directly at the location where the reaction takes place. However, compared to conventional heating it is difficult to achieve a homogeneous temperature profile. At least for large scale applicators, which are not small in all dimensions compared to the wavelength, one has standing wave patterns resulting from interference of different reflected and scattered parts of the microwave. Hence, the electromagnetic field shows a pattern consisting of field minima and maxima which result in thermal “cold” and “hot” spots. This paper describes a new scalable approach for an applicator at 2.45 GHz that achieves a homogeneous field and hence a homogeneous heating throughout the applicator.
Simulation for microwave heating of catalysts for CO<inf>2</inf> reduction to CO
2012 IEEE/MTT-S International Microwave Symposium Digest, 2012
ABSTRACT Using the reverse water gas shift reaction (RWGS) one can produce carbon monoxide from c... more ABSTRACT Using the reverse water gas shift reaction (RWGS) one can produce carbon monoxide from carbon dioxide with the help of a catalyst. As the reaction is endothermic external energy in form of heat has to be applied. In the project CO2RRECT (CO2-Reaction using Regenerative Energies and Catalytic Technologies) [1], one task is to construct an applicator where the heating of the catalysts for the reaction is done by microwaves at a frequency of 2.45 GHz. This paper describes the simulation of such an applicator.
The performance of a lithium ion cell is strongly related to the temperature. Therefore it is imp... more The performance of a lithium ion cell is strongly related to the temperature. Therefore it is important to under-stand the process of heat generation and dissipation inside a single cell but also in battery packs since this is also closely coupled to safety issues. In this study, commercial 18650 lithium ion cells with LiMn 2 O 4 cathodes as well as 20Ah pouch cells with LiFePO 4 cathodes were tested under isoperibolic and adiabatic conditions in an accelerating rate calorimeter (THT Company) to investigate the heat effects during cycling. Isoperibolic investigations in the range from 25 to 60°C show that the applied environmental temperature does not largely influence the battery thermal behavior. At 1C rate the maximum temperature increase over three cycles was 4°C almost independent of the environmental temperature. Additionally, the heat capacity and calo-rimeter constant were measured after calibration using cylindrical dummy cells made of AlMgSi 0.5 with the cell dimensions. B...
F 2 Melcher Modeling and simulation
Modeling and simulation of the thermal behavior of Li-ion cells
The thermal behavior of Li-ion cells is an important issue with regard to safety considerations. ... more The thermal behavior of Li-ion cells is an important issue with regard to safety considerations. Therefore, in order to construct a safe Lithium based battery system for use in electrical cars or large stationary electrochemical storage the behavior of the Li-ion cell has to be known under varying conditions. At present the control of the charge and discharge process, respectively, as well as the temperature monitoring and control is achieved by so called battery management systems (BMS) which mostly rely on relative simple charging and discharging algorithms due to the lack of a complete data base. One of the objectives of this work is to gain a better understanding of the temperature increase within the cell consider-ing different heat sources under normal working conditions but also under abuse condition with regard to the so called " thermal runaway " . Therefore a mathematical multi-scale multi-domain model (MSMD) has been developed based on a three-dimensional therma...
Simulationsmethoden in der Werkstoffkunde
Der Wachstumsmarkt Werkstoffsimulation
Conversion of EBSD data by a quaternion based algorithm to be used for grain structure simulations
CO2 Reduction to CO Using a Microwave Heated Catalyst
MACOS - Microwave Assisted Ablatation of Contaminated Concrete Surfaces - Modeling and Experiments
A Thermoelastic Model for Microwave Ablation of Concrete Karlsruhe Institute of Technology, Karlsruhe, Germany
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Papers by Andreas Melcher