Mathematical modeling and reliability analysis of a 3D Li-ion battery

The three-dimensional (3D) Li-ion battery presents an effective solution to issues affecting its two-dimensional counterparts, as it is able to attain high energy capacities for the same areal footprint without sacrificing power density. A 3D battery has key structural features extending in and fully utilizing 3D space, allowing it to achieve greater reliability and longevity. This study applies an electrochemical-thermal coupled model to a checkerboard array of alternating positive and negative electrodes in a 3D architecture with either square or circular electrodes. The mathematical model comprises the transient conservation of charge, species, and energy together with electroneutrality, constitutive relations and relevant initial and boundary conditions. A reliability analysis carried out to simulate malfunctioning of either a positive or negative electrode reveals that although there are deviations in electrochemical and thermal behavior for electrodes adjacent to the malfunctioning electrode as compared to that in a fully-functioning array, there is little effect on electrodes further away, demonstrating the redundancy that a 3D electrode array provides. The results demonstrate that implementation of 3D batteries allow it to reliably and safely deliver power even if a component malfunctions, a strong advantage over conventional 2D batteries

Hydrodynamic voltammetry at a rocking disc electrode:theory versus experiment

Rocking disc electrode voltammetry (RoDE) is introduced as an experimentally convenient and versatile alternative to rotating disc voltammetry. A 1.6 mm diameter disc electrode is employed with an overall rocking angle of θ = 90 degree applied over a frequency range of 0.83 Hz to 25 Hz. For a set of known aqueous redox systems (the oxidation of Fe(CN)64- in 1 M KCl, the reduction of Ru(NH3)63+ in 0.1 M KCl, the oxidation of hydroquinone in 0.1 M pH 7 phosphate buffer, the oxidation of I- in 0.125 M H2SO4, and the reduction of H+ in 1 M KCl) the mass transport controlled limiting current Ilim is demonstrated to follow in good approximation the Levich-type expression Ilim=0.111 nFAcD2/3v-1/6√Θf with n, the number of electrons transferred per molecule diffusing to the electrode surface, F, the Faraday constant, A, the geometric area, c, the concentration of the active redox species, D, the diffusion coefficient, v, the kinematic viscosity, θ is the overall rocking angle in degree, and f, the rocking rate in Hz. Quantitative theory is developed based on a two-dimensional (2D) axisymmetric laminar flow model accounting for the conservation of mass, momentum and species along with the kinematic analysis of a "four-bar mechanism" to obtain the rocking motion.</p

Hydrodynamic voltammetry at a rocking disc electrode:theory versus experiment

Rocking disc electrode voltammetry (RoDE) is introduced as an experimentally convenient and versatile alternative to rotating disc voltammetry. A 1.6 mm diameter disc electrode is employed with an overall rocking angle of θ = 90 degree applied over a frequency range of 0.83 Hz to 25 Hz. For a set of known aqueous redox systems (the oxidation of Fe(CN)64- in 1 M KCl, the reduction of Ru(NH3)63+ in 0.1 M KCl, the oxidation of hydroquinone in 0.1 M pH 7 phosphate buffer, the oxidation of I- in 0.125 M H2SO4, and the reduction of H+ in 1 M KCl) the mass transport controlled limiting current Ilim is demonstrated to follow in good approximation the Levich-type expression Ilim=0.111 nFAcD2/3v-1/6√Θf with n, the number of electrons transferred per molecule diffusing to the electrode surface, F, the Faraday constant, A, the geometric area, c, the concentration of the active redox species, D, the diffusion coefficient, v, the kinematic viscosity, θ is the overall rocking angle in degree, and f, the rocking rate in Hz. Quantitative theory is developed based on a two-dimensional (2D) axisymmetric laminar flow model accounting for the conservation of mass, momentum and species along with the kinematic analysis of a "four-bar mechanism" to obtain the rocking motion.</p

Mathematical Modeling of Transport Phenomena in Polymer Electrolyte and Direct Methanol Fuel Cells

This thesis deals with modeling of two types of fuel cells:the polymer electrolyte fuel cell (PEFC) and the directmethanol fuel cell (DMFC), for which we address four majorissues: a) mass transport limitations; b) water management(PEFC); c) gas management (DMFC); d) thermal management. Four models have been derived and studied for the PEFC,focusing on the cathode. The first exploits the slenderness ofthe cathode for a two-dimensional geometry, leading to areduced model, where several nondimensional parameters capturethe behavior of the cathode. The model was extended to threedimensions, where four di.erent flow distributors were studiedfor the cathode. A quantitative comparison shows that theinterdigitated channels can sustain the highest currentdensities. These two models, comprising isothermal gasphaseflow, limit the studies to (a). Returning to a two-dimensionalgeometry of the PEFC, the liquid phase was introduced via aseparate flow model approach for the cathode. In addition toconservation of mass, momentum and species, the model wasextended to consider simultaneous charge and heat transfer forthe whole cell. Di.erent thermal, flow fields, and hydrodynamicconditions were studied, addressing (a), (b) and (d). A scaleanalysis allowed for predictions of the cell performance priorto any computations. Good agreement between experiments with asegmented cell and the model was obtained. A liquid-phase model, comprising conservation of mass,momentum and species, was derived and analyzed for the anode ofthe DMFC. The impact of hydrodynamic, electrochemical andgeometrical features on the fuel cell performance were studied,mainly focusing on (a). The slenderness of the anode allows theuse of a narrow-gap approximation, leading to a reduced model,with benefits such as reduced computational cost andunderstanding of the physical trends prior to any numericalcomputations. Adding the gas-phase via a multiphase mixtureapproach, the gas management (c) could also be studied.Experiments with a cell, equipped with a transparent end plate,allowed for visualization of the flow in the anode, as well asvalidation of the two-phase model. Good agreement betweenexperiments and the model was achieved. Keywords:Fuel cell; DMFC; PEFC; one-phase; two-phase;model; visual cell; segmented cell; scale analysis; asymptoticanalysis

Mathematical Modeling of Transport Phenomena in Polymer Electrolyte and Direct Methanol Fuel Cells

This thesis deals with modeling of two types of fuel cells:the polymer electrolyte fuel cell (PEFC) and the directmethanol fuel cell (DMFC), for which we address four majorissues: a) mass transport limitations; b) water management(PEFC); c) gas management (DMFC); d) thermal management. Four models have been derived and studied for the PEFC,focusing on the cathode. The first exploits the slenderness ofthe cathode for a two-dimensional geometry, leading to areduced model, where several nondimensional parameters capturethe behavior of the cathode. The model was extended to threedimensions, where four di.erent flow distributors were studiedfor the cathode. A quantitative comparison shows that theinterdigitated channels can sustain the highest currentdensities. These two models, comprising isothermal gasphaseflow, limit the studies to (a). Returning to a two-dimensionalgeometry of the PEFC, the liquid phase was introduced via aseparate flow model approach for the cathode. In addition toconservation of mass, momentum and species, the model wasextended to consider simultaneous charge and heat transfer forthe whole cell. Di.erent thermal, flow fields, and hydrodynamicconditions were studied, addressing (a), (b) and (d). A scaleanalysis allowed for predictions of the cell performance priorto any computations. Good agreement between experiments with asegmented cell and the model was obtained. A liquid-phase model, comprising conservation of mass,momentum and species, was derived and analyzed for the anode ofthe DMFC. The impact of hydrodynamic, electrochemical andgeometrical features on the fuel cell performance were studied,mainly focusing on (a). The slenderness of the anode allows theuse of a narrow-gap approximation, leading to a reduced model,with benefits such as reduced computational cost andunderstanding of the physical trends prior to any numericalcomputations. Adding the gas-phase via a multiphase mixtureapproach, the gas management (c) could also be studied.Experiments with a cell, equipped with a transparent end plate,allowed for visualization of the flow in the anode, as well asvalidation of the two-phase model. Good agreement betweenexperiments and the model was achieved. Keywords:Fuel cell; DMFC; PEFC; one-phase; two-phase;model; visual cell; segmented cell; scale analysis; asymptoticanalysis

Föreningsaktiv eller inte? : En studie om idrott och fysisk aktivitet bland högstadieelever

Sport is the biggest movement in Sweden and among youth is seen as the most important and one of the most prestigious leisure-time activities. Riksidrottsförbundet (RF) is the main organization of the Swedish sport movement. It receives funding from the government in order to represent and develop the Swedish sports clubs. The government’s choice to support sport within RF happens at the expense of other sports, for example skateboarding. Many youths today choose to engage in sport and/or physical activities outside the club activities. This study aims to map and analyze sport and physical activities within and outside the club activities, among ninth graders (15-16 year) in one school in Umeå kommun. Fifty-six pupils, in three classes participated in the survey and their answers are the result of this study. The result showed a broad amount of different sport and physical activities among the youths. Many youths quit their involvement within sport club activities in order to engage in sport and/or physical activities outside the club activities. The survey also showed differences in the youths motives of sport and/or physical activities within and outside the club activities

Production improvement using Discrete Event Simulation : case study of Volvo Penta engine production line

The global market forces manufacturers to minimise costs, meet production schedules, and improve productivity to stay competitive. The produced products require higher customisations, which are affecting the complexity of the production system. Companies seeking methods and tools to improve their production system. One of these is Discrete Event Simulation (DES), which can be used to analyse the production system without affecting the real system. The limitations of the systems, are often known as bottlenecks. The bottleneck limits the performance of the production system to reach its maximum efficiency. This study, investigates the use of simulation in manual assembly lines, at Volvo Penta in Vara. The production system produces over 300 variants of engines, divided into three product families. The addressed problem, is that manual work and difference in processing times for each variant cause variation, which in turn, leads to bottlenecks. The required data was collected at the company and a simulation model was developed. During the analysis of the current state model, the main bottleneck of the system was found, by analysing buffer allocation-, utilisation-, and shifting bottleneck detection charts. Based on the analysis, three scenarios were developed to minimise the waiting portion of the bottleneck of the system. In the third scenario, one operator was allocated to the bottleneck, which in turn, eliminated the waiting potion. Additional four scenarios were developed with the objective to increase the throughput (TH) of the system. However, the bottleneck moved after each additional scenario. Based on the analysis of the performed scenarios, three proposed improvements were identified. The first improvement was to reschedule one engine family from the production line. The second, was to dedicate one operator directly to the bottleneck and finally, the third, prioritise and relocate operators to certain areas in the production line. In conclusion, simulation can be used to analyse manual production lines. However, simulating variation caused by manual work, requires a high amount of data. Furthermore, the combination of the proposed improvements has increased the TH of the system by 12 %, in comparison to the current state results and similarly used existing resources

Föreningsaktiv eller inte? : En studie om idrott och fysisk aktivitet bland högstadieelever

Sport is the biggest movement in Sweden and among youth is seen as the most important and one of the most prestigious leisure-time activities. Riksidrottsförbundet (RF) is the main organization of the Swedish sport movement. It receives funding from the government in order to represent and develop the Swedish sports clubs. The government’s choice to support sport within RF happens at the expense of other sports, for example skateboarding. Many youths today choose to engage in sport and/or physical activities outside the club activities. This study aims to map and analyze sport and physical activities within and outside the club activities, among ninth graders (15-16 year) in one school in Umeå kommun. Fifty-six pupils, in three classes participated in the survey and their answers are the result of this study. The result showed a broad amount of different sport and physical activities among the youths. Many youths quit their involvement within sport club activities in order to engage in sport and/or physical activities outside the club activities. The survey also showed differences in the youths motives of sport and/or physical activities within and outside the club activities

Production improvement using Discrete Event Simulation : case study of Volvo Penta engine production line

The global market forces manufacturers to minimise costs, meet production schedules, and improve productivity to stay competitive. The produced products require higher customisations, which are affecting the complexity of the production system. Companies seeking methods and tools to improve their production system. One of these is Discrete Event Simulation (DES), which can be used to analyse the production system without affecting the real system. The limitations of the systems, are often known as bottlenecks. The bottleneck limits the performance of the production system to reach its maximum efficiency. This study, investigates the use of simulation in manual assembly lines, at Volvo Penta in Vara. The production system produces over 300 variants of engines, divided into three product families. The addressed problem, is that manual work and difference in processing times for each variant cause variation, which in turn, leads to bottlenecks. The required data was collected at the company and a simulation model was developed. During the analysis of the current state model, the main bottleneck of the system was found, by analysing buffer allocation-, utilisation-, and shifting bottleneck detection charts. Based on the analysis, three scenarios were developed to minimise the waiting portion of the bottleneck of the system. In the third scenario, one operator was allocated to the bottleneck, which in turn, eliminated the waiting potion. Additional four scenarios were developed with the objective to increase the throughput (TH) of the system. However, the bottleneck moved after each additional scenario. Based on the analysis of the performed scenarios, three proposed improvements were identified. The first improvement was to reschedule one engine family from the production line. The second, was to dedicate one operator directly to the bottleneck and finally, the third, prioritise and relocate operators to certain areas in the production line. In conclusion, simulation can be used to analyse manual production lines. However, simulating variation caused by manual work, requires a high amount of data. Furthermore, the combination of the proposed improvements has increased the TH of the system by 12 %, in comparison to the current state results and similarly used existing resources