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Kaoru Maruta - One of the best experts on this subject based on the ideXlab platform.
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radiation extinction limit of counterflow premixed lean methane air flames
Combustion and Flame, 1997Co-Authors: Yiguang Ju, Kaoru Maruta, Takashi NiiokaAbstract:Abstract The application of the laminar flamelet concept to turbulent flame modeling requires a detailed understanding of Stretched laminar flames. In this study, we used numerical methods, including are-length continuation, to simulate the extinction characteristics of counterflow premixed fuel-lean, methane-air flames. Attention was primarily paid to the effect of radiative heat loss on the extinction characteristics of these flames. The results show that at medium to low values of the Stretch Rate, the radiative heat loss has a particularly strong impact on the counterflow premixed fuel-lean, methane-air flames. It was also found that, in addition to the Stretch extinction limit at a High Stretch Rate, there exits a radiation extinction limit at a low Stretch Rate. Furthermore, the relationship between these two extinction limits and the equivalence ratio is obtained.
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On the extinction limit and flammability limit of non-adiabatic Stretched methane-air premixed flames
Journal of Fluid Mechanics, 1997Co-Authors: Hongsheng Guo, Kaoru Maruta, Fengshan LiuAbstract:Extinction limits and the lean flammability limit of non-adiabatic Stretched premixed methane–air flames are investigated numerically with detailed chemistry and two different Planck mean absorption coefficient models. Attention is paid to the combined effect of radiative heat loss and Stretch at low Stretch Rate. It is found that for a mixture at an equivalence ratio lower than the standard lean flammability limit, a modeRate Stretch can strengthen the combustion and allow burning. The flame is extinguished at a High Stretch Rate due to Stretch and is quenched at a low Stretch Rate due to radiation loss. A O-shaped curve of flame temperature versus Stretch Rate with two distinct extinction limits, a radiation extinction limit and a Stretch extinction limit respectively on the left- and right-hand sides, is obtained. A C-shaped curve showing the flammability limit of the Stretched methane–air flame is obtained by plotting these two extinction limits in the mixture strength coordinate. A good agreement is shown on comparing the predicted results with the experimental data. For equivalence ratio larger than a critical value, it is found that the O-shaped temperature curve opens up in the middle of the stable branch, so that the stable branch divides into two stable flame branches; a weak flame branch and a normal flame branch. The weak flame can survive between the radiation extinction limit and the opening point (jump limit) while the normal flame branch can survive from its Stretch extinction limit to zero Stretch Rate. Finally, a G-shaped curve showing both extinction limits and jump limits of Stretched methane–air flames is presented. It is found that the critical equivalence ratio for opening up corresponds to the standard flammability limit measured in microgravity. Furthermore, the results show that the flammability limit (inferior limit) of the Stretched methane–air flame is lower than the standard flammability limit because flames are strengthened by a modeRate Stretch at Lewis number less than unity.
Takashi Niioka - One of the best experts on this subject based on the ideXlab platform.
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radiation extinction limit of counterflow premixed lean methane air flames
Combustion and Flame, 1997Co-Authors: Yiguang Ju, Kaoru Maruta, Takashi NiiokaAbstract:Abstract The application of the laminar flamelet concept to turbulent flame modeling requires a detailed understanding of Stretched laminar flames. In this study, we used numerical methods, including are-length continuation, to simulate the extinction characteristics of counterflow premixed fuel-lean, methane-air flames. Attention was primarily paid to the effect of radiative heat loss on the extinction characteristics of these flames. The results show that at medium to low values of the Stretch Rate, the radiative heat loss has a particularly strong impact on the counterflow premixed fuel-lean, methane-air flames. It was also found that, in addition to the Stretch extinction limit at a High Stretch Rate, there exits a radiation extinction limit at a low Stretch Rate. Furthermore, the relationship between these two extinction limits and the equivalence ratio is obtained.
Fengshan Liu - One of the best experts on this subject based on the ideXlab platform.
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On the extinction limit and flammability limit of non-adiabatic Stretched methane-air premixed flames
Journal of Fluid Mechanics, 1997Co-Authors: Hongsheng Guo, Kaoru Maruta, Fengshan LiuAbstract:Extinction limits and the lean flammability limit of non-adiabatic Stretched premixed methane–air flames are investigated numerically with detailed chemistry and two different Planck mean absorption coefficient models. Attention is paid to the combined effect of radiative heat loss and Stretch at low Stretch Rate. It is found that for a mixture at an equivalence ratio lower than the standard lean flammability limit, a modeRate Stretch can strengthen the combustion and allow burning. The flame is extinguished at a High Stretch Rate due to Stretch and is quenched at a low Stretch Rate due to radiation loss. A O-shaped curve of flame temperature versus Stretch Rate with two distinct extinction limits, a radiation extinction limit and a Stretch extinction limit respectively on the left- and right-hand sides, is obtained. A C-shaped curve showing the flammability limit of the Stretched methane–air flame is obtained by plotting these two extinction limits in the mixture strength coordinate. A good agreement is shown on comparing the predicted results with the experimental data. For equivalence ratio larger than a critical value, it is found that the O-shaped temperature curve opens up in the middle of the stable branch, so that the stable branch divides into two stable flame branches; a weak flame branch and a normal flame branch. The weak flame can survive between the radiation extinction limit and the opening point (jump limit) while the normal flame branch can survive from its Stretch extinction limit to zero Stretch Rate. Finally, a G-shaped curve showing both extinction limits and jump limits of Stretched methane–air flames is presented. It is found that the critical equivalence ratio for opening up corresponds to the standard flammability limit measured in microgravity. Furthermore, the results show that the flammability limit (inferior limit) of the Stretched methane–air flame is lower than the standard flammability limit because flames are strengthened by a modeRate Stretch at Lewis number less than unity.
Biglione Jordan - One of the best experts on this subject based on the ideXlab platform.
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Numerical simulation and optimization of the injection blow molding of polypropylene bottles - a single stage process
'Springer Science and Business Media LLC', 2016Co-Authors: Biglione Jordan, Bereaux Yves, Charmeau Jean-yves, Balcaen Jean, Chhay S.Abstract:International audienceSingle stage injection blow molding process, without preform storage and reheat, could be run on a standard injection molding machine, with the aim of producing short series of specific hollow parts. The polypropylene bottles are blow molded right after being injected. This implies that the preform has to remain sufficiently malleable to be blown while being viscous enough to avoid being pierced during the blow molding stage. These constraints lead to a small processing window, and so the process takes place between the melting temperature and the crystallization temperature, where the polypropylene is in its molten state but cool enough to enhance its viscosity without crystallizing. This single stage process introduces temperature gradients, High Stretch Rate and High cooling Rate. Melt rheometry tests were performed to characterize the polymer behavior in the temperature range of the process, as well as Differential Scanning Calorimetry. A viscous Cross model is used with the thermal dependence assumed by an Arrhenius law. The process is simulated through a finite element code (POLYFLOW) in the ANSYS Workbench framework. The geometry allows an axisymmetric approach. The transient simulation is run under anisothermal conditions and viscous heating is taken into account. Sensitivity studies are carried out and reveal the influence of process parameters such as the material behavior, the blowing pressure and the initial temperature field. Thickness measurements using image analysis are performed and the simulation results are compared to the experimental ones. The simulation shows broad agreements with the experimental results. An optimization loop is run to determine the optimal initial thickness repartition. Design points are defined along the preform and the optimization modifies the thickness at these locations
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Simulation et optimisation du procédé d'injection soufflage cycle chaud
HAL CCSD, 2015Co-Authors: Biglione JordanAbstract:Single stage injection blow molding process, without preform storage and reheat, could be run on a standard injection molding machine, with the aim of producing short series of specific hollow parts. The polypropylene bottles are blown right after being injected. The preform has to remain sufficiently malleable to be blown while being viscous enough to avoid being pierced during the blow molding stage. These constraints lead to a small processing window, and so the process takes place between the melting temperature and the crystallization temperature, where the polypropylene is in his molten state but cool enough to enhance its viscosity without crystallizing. This single stage process introduces temperature gradients, molecular orientation, High Stretch Rate and High cooling Rate. Melt rheometry tests were performed to characterize the polymer behavior in the temperature range of the process, as well as Differential Scanning Calorimetry. A viscous Cross model is used with the thermal dependence assumed by an Arrhenius law. The process is simulated through a finite element code (POLYFLOW) in the Ansys Workbench framework. The geometry allows an axisymmetric approach. The transient simulation is run under anisothermal conditions and viscous heating is taken into account. Thickness measurements using image analysis are done and the simulation results are compared to the experimental ones. The experimental measurements are done by analizing tomography datas. The simulation shows good agreements with the experimental results. The existence of elongational strain as well as shear strain during the blowing after contact with the mold is discussed. An optimization loop is run to determine an optimal initial thickness repartition by the use of a Predictor/Corrector method to minimize a given objective function. Design points are defined along the preform and the optimization modifies the thickness at these locations. This method is compared to the Downhill Simplex Method and shows better efficiency.Le procédé d'injection soufflage est rendu accessible aux presses d'injection standard à travers le procédé d'injection soufflage cycle chaud, sans stockage puis réchauffe de la préforme. Le but étant de rendre accessible la production de petites séries de pièces creuses à des entreprises possédant un parc machine de presse à injecter. Les pièces sont réalisées en polypropylène et sont soufflées juste après avoir été injectées. Ce processus implique que la préforme se doit d'être suffisamment malléable pour être soufflée mais suffisamment visqueuse pour éviter de se rompre durant la phase de soufflage. Ces contraintes conduisent à une fenêtre de mise en oeuvre réduite, comprise entre la température de fusion du polymère et la température de cristallisation, soit le domaine ou le polypropylène est à l'état amorphe et suffisamment froid pour avoir une viscosité conséquente sans cristalliser. Ce procédé cycle chaud implique des gradients de température, de grands taux d'étirages et d'importantes cinétiques de refroidissement. Des mesures de rhéométrie à l'état fondu sont réalisées pour identifier le comportement de la matière dans la plage de température du procédé, de même que des tests de calorimétrie différentielle. L'observation du procédé et l'étude de la cristallisation du matériau permettent de supposer que ce dernier reste à l'état fondu durant la phase de soufflage. Un modèle rhéologique de Cross est utilisé, avec la dépendance thermique prise en compte par une loi d'Arrhénius. Le procédé est simulé à l'aide d'un logiciel de calcul par éléments finis dédié aux écoulements de fluides complexes (POLYFLOW) dans l'espace de travail ANSYS Workbench. La géométrie autorise une approche axisymétrique, facilitant ainsi la modélisation. Le calcul transitoire est lancé sous conditions anisothermes et l'auto-échauffement est considéré. Des études de sensibilité sont réalisées et révèlent l'influence de paramètres procédé tels que le comportement du matériau, la pression de soufflage et le champ de température initial. Des mesures d'épaisseurs sont réalisées en utilisant une méthode de traitement d'image permettant l'analyse des images numérisées de pièces découpées et des images issues de tomographie X des pièces. Les résultats simulés sont comparés aux mesures expérimentales. Le modèle présente les mêmes tendances que les mesures. L'existence de déformations élongationnelles, mais aussi par cisaillement lors du soufflage après contact avec le moule, est discutée. Une boucle d'optimisation est mise en place afin de déterminer numériquement la géométrie optimale de préforme. Des points de contrôle sont placés le long de la préforme et l'algorithme d'optimisation modifie les épaisseurs à ces points
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Simulation et Optimisation du Procédé d'Injection Soufflage Cycle Chaud
HAL CCSD, 2015Co-Authors: Biglione JordanAbstract:Single stage injection blow molding process, without preform storage and reheat,could be run on a standard injection molding machine, with the aim of producingshort series of specific hollow parts. The polypropylene bottles are blown right af-ter being injected. The preform has to remain sufficiently malleable to be blownwhile being viscous enough to avoid being pierced during the blow molding stage.These constraints lead to a small processing window, and so the process takes placebetween the melting temperature and the crystallization temperature, where the po-lypropylene is in his molten state but cool enough to enhance its viscosity withoutcrystallizing. This single stage process introduces temperature gradients, molecu-lar orientation, High Stretch Rate and High cooling Rate. Melt rheometry tests wereperformed to characterize the polymer behavior in the temperature range of theprocess, as well as Differential Scanning Calorimetry. A viscous Cross model is usedwith the thermal dependence assumed by an Arrhenius law. The process is simulatedthrough a finite element code (POLYFLOW) in the Ansys Workbench framework.The geometry allows an axisymmetric approach. The transient simulation is rununder anisothermal conditions and viscous heating is taken into account. Thicknessmeasurements using image analysis are done and the simulation results are compa-red to the experimental ones. The experimental measurements are done by analizingtomography datas. The simulation shows good agreements with the experimental re-sults. The existence of elongational strain as well as shear strain during the blowingafter contact with the mold is discussed. An optimization loop is run to determinean optimal initial thickness repartition by the use of a Predictor/Corrector methodto minimize a given objective function. Design points are defined along the pre-form and the optimization modifies the thickness at these locations. This method iscompared to the Downhill Simplex Method and shows better efficiency.Le procédé d'injection soufflage est rendu accessible aux presses d'injection standard à travers le procédé d'injection soufflage cycle chaud, sans stockage puis réchauffe de la préforme. Le but étant de rendre accessible la production de petites séries de pièces creuses à des entreprises possédant un parc machine de presse à injecter. Les pièces sont réalisées en polypropylène et sont soufflées juste après avoir été injectées. Ce processus implique que la préforme se doit d'être suffisamment malléable pour être soufflée mais suffisamment visqueuse pour éviter de se rompre durant la phase de soufflage. Ces contraintes conduisent à une fenêtre de mise en œuvre réduite, comprise entre la température de fusion du polymère et la température de cristallisation, soit le domaine ou le polypropylène est à l'état amorphe et suffisamment froid pour avoir une viscosité conséquente sans cristalliser. Ce procédé cycle chaud implique des gradients de température, de grands taux d'étirages et d'importantes cinétiques de refroidissement. Des mesures de rhéométrie à l'état fondu sont réalisées pour identifier le comportement de la matière dans la plage de température du procédé, de même que des tests de calorimétrie différentielle. L'observation du procédé et l'étude de la cristallisation du matériau permettent de supposer que ce dernier reste à l'état fondu durant la phase de soufflage. Un modèle rhéologique de Cross est utilisé, avec la dépendance thermique prise en compte par une loi d'Arrhénius. Le procédé est simulé à l'aide d'un logiciel de calcul par éléments finis dédié aux écoulements de fluides complexes (POLYFLOW) dans l'espace de travail ANSYS Workbench. La géométrie autorise une approche axisymétrique, facilitant ainsi la modélisation. Le calcul transitoire est lancé sous conditions anisothermes et l'auto-échauffement est considéré. Des études de sensibilité sont réalisées et révèlent l'influence de paramètres procédé tels que le comportement du matériau, la pression de soufflage et le champ de température initial. Des mesures d'épaisseurs sont réalisées en utilisant une méthode de traitement d'image permettant l'analyse des images numérisées de pièces découpées et des images issues de tomographie X des pièces. Les résultats simulés sont comparés aux mesures expérimentales. Le modèle présente les mêmes tendances que les mesures.L'existence de déformations élongationnelles, mais aussi par cisaillement lors du soufflage après contact avec le moule, est discutée.Une boucle d'optimisation est mise en place afin de déterminer numériquement la géométrie optimale de préforme. Des points de contrôle sont placés le long de la préforme et l'algorithme d'optimisation modifie les épaisseurs à ces points
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Simulation and optimization of the injection blow molding single stage process
2015Co-Authors: Biglione JordanAbstract:Le procédé d'injection soufflage est rendu accessible aux presses d'injection standard à travers le procédé d'injection soufflage cycle chaud, sans stockage puis réchauffe de la préforme. Le but étant de rendre accessible la production de petites séries de pièces creuses à des entreprises possédant un parc machine de presse à injecter. Les pièces sont réalisées en polypropylène et sont soufflées juste après avoir été injectées. Ce processus implique que la préforme se doit d'être suffisamment malléable pour être soufflée mais suffisamment visqueuse pour éviter de se rompre durant la phase de soufflage. Ces contraintes conduisent à une fenêtre de mise en oeuvre réduite, comprise entre la température de fusion du polymère et la température de cristallisation, soit le domaine ou le polypropylène est à l'état amorphe et suffisamment froid pour avoir une viscosité conséquente sans cristalliser. Ce procédé cycle chaud implique des gradients de température, de grands taux d'étirages et d'importantes cinétiques de refroidissement. Des mesures de rhéométrie à l'état fondu sont réalisées pour identifier le comportement de la matière dans la plage de température du procédé, de même que des tests de calorimétrie différentielle. L'observation du procédé et l'étude de la cristallisation du matériau permettent de supposer que ce dernier reste à l'état fondu durant la phase de soufflage. Un modèle rhéologique de Cross est utilisé, avec la dépendance thermique prise en compte par une loi d'Arrhénius. Le procédé est simulé à l'aide d'un logiciel de calcul par éléments finis dédié aux écoulements de fluides complexes (POLYFLOW) dans l'espace de travail ANSYS Workbench. La géométrie autorise une approche axisymétrique, facilitant ainsi la modélisation. Le calcul transitoire est lancé sous conditions anisothermes et l'auto-échauffement est considéré. Des études de sensibilité sont réalisées et révèlent l'influence de paramètres procédé tels que le comportement du matériau, la pression de soufflage et le champ de température initial. Des mesures d'épaisseurs sont réalisées en utilisant une méthode de traitement d'image permettant l'analyse des images numérisées de pièces découpées et des images issues de tomographie X des pièces. Les résultats simulés sont comparés aux mesures expérimentales. Le modèle présente les mêmes tendances que les mesures. L'existence de déformations élongationnelles, mais aussi par cisaillement lors du soufflage après contact avec le moule, est discutée. Une boucle d'optimisation est mise en place afin de déterminer numériquement la géométrie optimale de préforme. Des points de contrôle sont placés le long de la préforme et l'algorithme d'optimisation modifie les épaisseurs à ces points.Single stage injection blow molding process, without preform storage and reheat, could be run on a standard injection molding machine, with the aim of producing short series of specific hollow parts. The polypropylene bottles are blown right after being injected. The preform has to remain sufficiently malleable to be blown while being viscous enough to avoid being pierced during the blow molding stage. These constraints lead to a small processing window, and so the process takes place between the melting temperature and the crystallization temperature, where the polypropylene is in his molten state but cool enough to enhance its viscosity without crystallizing. This single stage process introduces temperature gradients, molecular orientation, High Stretch Rate and High cooling Rate. Melt rheometry tests were performed to characterize the polymer behavior in the temperature range of the process, as well as Differential Scanning Calorimetry. A viscous Cross model is used with the thermal dependence assumed by an Arrhenius law. The process is simulated through a finite element code (POLYFLOW) in the Ansys Workbench framework. The geometry allows an axisymmetric approach. The transient simulation is run under anisothermal conditions and viscous heating is taken into account. Thickness measurements using image analysis are done and the simulation results are compared to the experimental ones. The experimental measurements are done by analizing tomography datas. The simulation shows good agreements with the experimental results. The existence of elongational strain as well as shear strain during the blowing after contact with the mold is discussed. An optimization loop is run to determine an optimal initial thickness repartition by the use of a Predictor/Corrector method to minimize a given objective function. Design points are defined along the preform and the optimization modifies the thickness at these locations. This method is compared to the Downhill Simplex Method and shows better efficiency
Yiguang Ju - One of the best experts on this subject based on the ideXlab platform.
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radiation extinction limit of counterflow premixed lean methane air flames
Combustion and Flame, 1997Co-Authors: Yiguang Ju, Kaoru Maruta, Takashi NiiokaAbstract:Abstract The application of the laminar flamelet concept to turbulent flame modeling requires a detailed understanding of Stretched laminar flames. In this study, we used numerical methods, including are-length continuation, to simulate the extinction characteristics of counterflow premixed fuel-lean, methane-air flames. Attention was primarily paid to the effect of radiative heat loss on the extinction characteristics of these flames. The results show that at medium to low values of the Stretch Rate, the radiative heat loss has a particularly strong impact on the counterflow premixed fuel-lean, methane-air flames. It was also found that, in addition to the Stretch extinction limit at a High Stretch Rate, there exits a radiation extinction limit at a low Stretch Rate. Furthermore, the relationship between these two extinction limits and the equivalence ratio is obtained.