The Experts below are selected from a list of 36798 Experts worldwide ranked by ideXlab platform
W. D. Gonzalez - One of the best experts on this subject based on the ideXlab platform.
-
Analytical study of the Energy Rate Balance equation for the magnetospheric storm-ring current
Annales Geophysicae, 1998Co-Authors: A. L. Gonzalez, W. D. GonzalezAbstract:We present some results of the analytical integration of the Energy Rate Balance equation, assuming that the input Energy Rate is proportional to the azimuthal interplanetary electric field, E _ y , and can be described by simple rectangular or triangular functions, as approximations to the frequently observed shapes of E _ y , especially during the passage of magnetic clouds. The input function is also parametrized by a reconnection-transfer efficiency factor α (which is assumed to vary between 0.1 and 1). Our aim is to solve the Balance equation and derive values for the decay parameter τ compatible with the observed Dst peak values. To facilitate the analytical integration we assume a constant value for τ through the main phase of the storm. The model is tested for two isolated and well-monitored intense storms. For these storms the analytical results are compared to those obtained by the numerical integration of the Balance equation, based on the interplanetary data collected by the ISEE-3 satellite, with the τ values parametrized close to those obtained by the analytical study. From the best fit between this numerical integration and the observed Dst the most appropriate values of τ are then determined. Although we specifically focus on the main phase of the storms, this numerical integration has been also extended to the recovery phase by an independent adjust. The results of the best fit for the recovery phase show that the values of τ may differ drastically from those corresponding to the main phase. The values of the decay parameter for the main phase of each event, τ_ m , are found to be very sensitive to the adopted efficiency factor, α, decreasing as this factor increases. For the recovery phase, which is characterized by very low values of the power input, the response function becomes almost independent of the value of α and the resulting values for the decay time parameter, τ_ r , do not vary greatly as α varies. As a consequence, the relative values of τ between the main and the recovery phase, τ_ m /τ_ r , can be greater or smaller than one as α varies from 0.1 to 1.
Yadav Pankaj - One of the best experts on this subject based on the ideXlab platform.
-
Effets du temps et effets de couplage thermomécanique dans les polymères
2019Co-Authors: Yadav PankajAbstract:L'étude du comportement mécanique et thermique des polymères est d'une importance capitale pour les applications techniques. Par conséquent, la capacité de prédire ces propriétés pour des plages étendues de fréquences de sollicitation et de température, est une forte motivation. Sur la base d'une combinaison expérimentale d'analyses rhéologiques mécaniques et thermiques (DMTA), des modèles phénoménologiques sont ainsi développés pour prédire le comportement viscoélastique linéaire des polymères avec l'utilisation traditionnelle du principe dit de "superposition temps-température (TTSP)". Lors de la mise en œuvre de ces modèles, la prise en compte (i) des effets liés à la température réelle de l'échantillon ou (ii) des effets induits par les couplages thermomécaniques n'est pas prise en compte. Cependant, les matériaux polymères sont très sensibles aux variations de température et même de faibles variations de température peuvent engendrées des sources de couplage thermomécanique ou de dissipation non négligeables dans le bilan d’énergie. L'applicabilité du TTSP dans ce contexte mérite d’être revisitée. Ainsi, une connaissance précise du comportement mécanique et thermique de cette classe de matériaux, dans le cadre de la thermodynamique des processus irréversibles, en tenant compte de l'effet dissipatif et du couplage thermomécanique, est nécessaire.Pour atteindre ces objectifs, la présente étude a été réalisée à partir d'une revue de la littérature sur le comportement thermomécanique des polymères vitreux et amorphes et du TTSP. Ensuite, nous avons rappelé le cadre théorique de la thermodynamique des processus irréversibles et sa mise en œuvre dans le formalisme des matériaux standards généralisés (GSM). Ainsi la température pu être considérée comme une variable d'état et les équations comportementales constitutives ont pu être dérivées d'un potentiel thermodynamique et de dissipation. Ce formalisme a également permis de définir puis de calculer les différentes sources de chaleur et la forme globale du bilan d’énergie.Deuxièmement, des mesures ont été effectuées pour caractériser les propriétés viscoélastiques linéaires en dessous de la température de transition vitreuse de certains polymères amorphes et rhéologiquement simples (PS, PMMA et PA-6.6). On a ensuite appliqué un TTSP classique utilisant une loi d'Arrhenius pour prédire le comportement viscoélastique linéaire sur une très large plage de température/fréquence, qui ne peut être atteinte expérimentalement. Une première série de mesures a été effectuée sur PS dans plusieurs laboratoires pour vérifier la réponse monochromatique à une charge monochromatique et construire une base de données de référence pour l'étalonnage et la validation des différentes procédures de correction (rigidité machine et déphasage électronique) de notre DMTA. Par la suite, des mesures thermographiques synchronisées ont été effectuées pour mesurer les variations de température de l'échantillon pendant les mesures DMTA. Ceci permet d'estimer l'énergie mécanique moyenne dissipée pendant un cycle ainsi que les pertes de chaleur et le couplage thermoélastique.Enfin, ces résultats expérimentaux ont été utilisés pour identifier les branches d'un modèle de Maxwell généralisé (MGM) en utilisant la méthode des moindres carrés non négatifs pour les 3 polymères différents. Dans chaque branche de ce modèle, la constante de temps viscoélastique et le module d'élasticité associé dépendent de la température (par une loi d'Arrhenius et une énergie d'activation préalablement déterminée expérimentalement). En utilisant le formalisme GSM, les différentes sources de chaleur (couplages thermomécaniques, dissipation) ont également été calculées. Le bilan énergétique a montré la prédominance des sources de couplages thermomécaniques. Pour conclure cette étude, nous avons montré qu'un MGM supposant l'hypothèse de matériau rhéologiquement simple est compatible avec le TTSP.The study of the mechanical and thermal behaviour of polymers is of prime importance for engineering applications. Therefore, the ability of predicting these properties for several decades of loading frequencies and/or several tens of degree Celsius, is a strong motivation. Based on experimental combination of mechanical and thermal rheological-analysis (DMTA), phenomenological models are thus developed to predict the linear viscoelastic behaviour of polymers with the traditional use of the so-called “time-temperature superposition principle (TTSP)”. While implementing these models, the consideration of (i) effects linked to the real temperature of the sample or of (ii) the time effects induced by thermo-mechanical couplings are not taken into account. However, polymer materials are very sensitive to temperature variations and even slight temperature variations can be due to thermo-mechanical coupling or dissipation sources. The TTSP applicability in such a context is thus not straightforward. Therefore, an accuRate knowledge of the mechanical and thermal behaviour of this class of materials, under the Thermodynamics of Irreversible processes, taking into account the dissipative effect and thermo-mechanical coupling, can become of prime importance.To achieve these objectives, the present study was performed starting from a literature review on the thermo-mechanical behaviour of vitreous and amorphous polymers and the TTSP. This was followed by understanding the theoretical framework of thermodynamics of irreversible processes and its implementation in the Generalized Standard Material (GSM) formalism. The theoretical framework of GSM allowed us to consider the temperature as an internal state variable and to derive the constitutive behavioural equations from a thermodynamic and a dissipation potential. This formalism also induced the possibilities to define and then compute the different heat sources involved in the heat diffusion equation.Second, measurements were performed to characterize the linear viscoelastic properties below the glass transition temperature of selected amorphous and rheologically simple polymers (PS, PMMA and PA-6.6). This was followed by the application of a classical TTSP using an Arrhenius law to predict the linear viscoelastic behaviour on a very large temperature/frequency range, which cannot be experimentally reachable. A first set of measurements was performed on PS in several laboratories to check for its monochromatic response to a monochromatic loading and build a reference database for the calibration and validation of different correction procedures (machine stiffness and electronic phase shift) of our DMTA. Later, synchronized thermography measurements were performed to measure the temperature variations of the sample during DMTA measurements. This allows for the estimation of the average mechanical Energy dissipated during one cycle together with the heat losses and thermoelastic coupling.Finally, these experimental results were used to identify the optimum branches of a generalized Maxwell model (GMM) using non negative least squares method for the 3 different polymers. In each branch of this model, the viscoelastic time constant and the associated elastic modulus depend on the temperature (through an Arrhenius law and an activation Energy determined previously experimentally). Using the GSM formalism, the different heat sources (thermomechanical couplings, dissipation) were also computed. The Energy Rate Balance showed the predominance of the thermomechanical couplings sources. To conclude this study, we stressed that a GMM assuming the rheological simple material hypothesis is TTSP compatible
A. L. Gonzalez - One of the best experts on this subject based on the ideXlab platform.
-
Analytical study of the Energy Rate Balance equation for the magnetospheric storm-ring current
Annales Geophysicae, 1998Co-Authors: A. L. Gonzalez, W. D. GonzalezAbstract:We present some results of the analytical integration of the Energy Rate Balance equation, assuming that the input Energy Rate is proportional to the azimuthal interplanetary electric field, E _ y , and can be described by simple rectangular or triangular functions, as approximations to the frequently observed shapes of E _ y , especially during the passage of magnetic clouds. The input function is also parametrized by a reconnection-transfer efficiency factor α (which is assumed to vary between 0.1 and 1). Our aim is to solve the Balance equation and derive values for the decay parameter τ compatible with the observed Dst peak values. To facilitate the analytical integration we assume a constant value for τ through the main phase of the storm. The model is tested for two isolated and well-monitored intense storms. For these storms the analytical results are compared to those obtained by the numerical integration of the Balance equation, based on the interplanetary data collected by the ISEE-3 satellite, with the τ values parametrized close to those obtained by the analytical study. From the best fit between this numerical integration and the observed Dst the most appropriate values of τ are then determined. Although we specifically focus on the main phase of the storms, this numerical integration has been also extended to the recovery phase by an independent adjust. The results of the best fit for the recovery phase show that the values of τ may differ drastically from those corresponding to the main phase. The values of the decay parameter for the main phase of each event, τ_ m , are found to be very sensitive to the adopted efficiency factor, α, decreasing as this factor increases. For the recovery phase, which is characterized by very low values of the power input, the response function becomes almost independent of the value of α and the resulting values for the decay time parameter, τ_ r , do not vary greatly as α varies. As a consequence, the relative values of τ between the main and the recovery phase, τ_ m /τ_ r , can be greater or smaller than one as α varies from 0.1 to 1.
Souza, Daniel Mazzete - One of the best experts on this subject based on the ideXlab platform.
-
Análise paramétrica e exergética de gerador de vapor alimentado pela incineração de resíduos sólidos urbanos
2020Co-Authors: Souza, Daniel MazzeteAbstract:Orientador: Prof. PhD. José Viriato Coelho VargasCoorientador: Dr. Wellington BalmantDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Mecânica. Defesa : Curitiba, 10/07/2020Inclui referências: p. 99-101Área de concentração: Fenômenos de Transporte e Engenharia TérmicaResumo: No cenário atual, o descarte do lixo é um dos maiores problemas enfrentados. A crescente ocupação territorial tem aumentado a geração desses resíduos além de limitar o espaço físico para sua destinação final. O impacto ambiental, resultado do mau gerenciamento do lixo, traduz-se na contaminação de solos, subsolos e cursos d'água, enchentes e erosões, grandes desgastes para a flora e fauna, além da poluição. A Recuperação Energética é hoje uma alternativa para a destinação dos resíduos sólidos urbanos (RSU). Dentre as tecnologias disponíveis, que aproveitam a energia calorífica contida nesses resíduos para uso como fonte de energia ou combustível, destaca-se a incineração. Diante do exposto, a presente dissertação traz como objetivo realizar a análise paramétrica e exergética do gerador de vapor alimentado pela incineração de resíduos sólidos urbanos (RSU) instalado nas dependências do NPDEAS. O modelo matemático combina os princípios da termodinâmica e da transferência de calor aplicados aos volumes de controle para cada componente do gerador de vapor (GV) e para uma turbina hipoteticamente instalada, bem como as reações de combustão, dada a composição química de uma amostra de RSU. Como resultado, foi obtido a área de troca térmica em cada trocador de calor, o comportamento paramétrico do sistema avaliado nos parâmetros de operação de maior impacto com vistas às eficiências de 1° e 2° Lei e à potência gerada na turbina, a configuração adequada em função dos parâmetros analisados a fim de se obter um sistema otimizado, bem como um extrato completo do sistema e um Balancete da taxa de exergia. Os melhores resultados, extraídos de dois cenários, mostraram que um ajuste otimizado dos parâmetros de operação é capaz de aumentar a potência na turbina em cerca de 100%, o rendimento energético e exergético do GV em 16% e 51,88%, e o rendimento energético e exergético do sistema de potência em cerca de 84%. A folha de Balancete de exergia mostra que somente 10% do aporte de energia é convertida em potência nessa instalação e que a exergia destruída pela combustão supera os 40%. A principal conclusão dessa dissertação é a capacidade do modelo matemático em simular e descrever fisicamente o sistema de incineração de RSU e geração de vapor assim como de cada um de seus componentes, podendo, portanto, prever seu comportamento frente a diversas condições de funcionamento, bem como identificar seus parâmetros de operação de maior impacto visando ao melhor uso de energias renováveis e maiores eficiências energéticas e exergéticas. Palavras-chave: Incineração de Resíduos Sólidos Urbanos. Combustão. Energia térmica. Exergia.Abstract: ABSTRACT In the current scenario, waste disposal is one of the biggest problems faced. The growing territorial occupation has increased the generation of this waste, besides limiting the physical space for its final destination. The environmental impact, as a result of poor waste management, translates into soil, subsoil and waterway contamination, floods and erosion, great wear and tear for flora and fauna, in addition to pollution. The Energy Recovery is today an alternative for the destination of municipal solid waste (MSW). Among the available technologies, which take advantage of the calorific Energy contained in these wastes for use as a source of Energy or fuel, incineration stands out. In view of the above, this dissertation aims to perform parametric and exergetic analysis of the steam generator fed by the incineration of solid urban waste installed in the NPDEAS premises. The mathematical model combines the principles of thermodynamics and heat transfer applied to the control volumes for each component of the steam generator (GV) and for a hypothetically installed turbine, as well as the combustion reactions, given the chemical composition of a MSW sample. As a result, the heat exchange area in each heat exchanger was obtained, the parametric behaviour of the system evaluated in the highest impact operating parameters with a view to 1st and 2nd Law efficiencies and the power geneRated in the turbine, the appropriate configuration as a function of the analyzed parameters in order to obtain an optimized system, as well as a complete system extract and an Energy Rate Balance. The best results, extracted from two scenarios, showed that an optimized adjustment of the operation parameters is able to increase the power in the turbine by about 100%, the energetic and exergetic efficiency of the GV by 16% and 51.88% and the energetic and exergetic efficiency of the power system by about 84%. The Energy Balance sheet shows that only 10% of the Energy input is converted into power in this plant and that the Energy destroyed by combustion exceeds 40%. The main conclusion of this dissertation is the ability of the mathematical model to physically simulate and describe the MSW incineration and steam generation system as well as each of its components, thus being able to predict its behavior under various operating conditions, as well as to identify its operating parameters of greater impact aiming at the best use of renewable energies and greater Energy and exergetic efficiencies. Keywords: Incineration of Urban Solid Waste. Combustion. Thermal Energy. Exerg
Patel Josh - One of the best experts on this subject based on the ideXlab platform.
-
Numerical Simulation of AFP Nip Point Temperature Prediction for Complex Geometries
2018Co-Authors: Harik Ramy, Grimsley, Brian W., Xia Kaishu, Herrera Jeremy, Patel JoshAbstract:Material placement at the ideal nip point temperature over complex surfaces with uniformity across the width of the compaction rollers results in optimized part properties for Automated Fiber Placement (AFP) processes. However, current AFP systems utilize heat control models and methodologies, based on multiple process parameters such as feed-Rate and orientation, that are mostly open-loop. Here, infrared (IR) heater input is calibRated as a function of process parameters during machine qualification. This work presents a numerical simulation to predict arrayed-infrared (AIR) emitter radiation onto a substRate that includes view factor implementation, IR radiative heat flow calculation, Energy Rate Balance, and a transient heat transfer model. The purpose of this numerical model is to predict nip point temperature on complex surfaces, serving as a baseline for a new arrayed-infrared (AIR) thermoset heater to improve AFP process control. It is anticipated that this simulation will accuRately control the temperature for high-speed AFP layup of complex geometries. An anticipated result of an AIR heater system is that material calibration and testing will be reduced as temperature is instantaneously monitored and controlled. Therefore, temperature across the roller width will be uniform during placement of complex parts, independent of their geometry