Pub Date : 2018-10-10DOI: 10.5772/INTECHOPEN.75987
H. P. A. D. Deus, M. Itskov
The time-dependent rheological behavior of the thixotropic fluids is presented in various industrial fields (cosmetics, food, oil, etc.). Usually, a couple of equations define constitutive model for thixotropic substances: a constitutive equation based on linear viscoelastic models and a rate equation (an equation related to the micro-structural evolution of the substance). Many constitutive models do not take into account the micro-structural dependence of the shear modulus and viscosity in the dynamic principles from which are developed. The modified Jeffreys model (con-sidering only one single micro-structure type) does not show this incoherence in its formulation. In this chapter, a constitutive model for thixotropic fluids, based on modified Jeffreys model, is presented with the addition of one more micro-structure type, besides of comments on some possible generalizations. The rheological coherence of this constitutive model and thermodynamic consistency are analyzed too. This model takes into account a simple isothermal laminar shear flows, and the micro-structures dynamics are relate to Brownian motion and de Gennes Reptation model via the Smoluchowski ™ s coagulation theory.
{"title":"On the Thermodynamic Consistency of a Two Micro-Structured Thixotropic Constitutive Model","authors":"H. P. A. D. Deus, M. Itskov","doi":"10.5772/INTECHOPEN.75987","DOIUrl":"https://doi.org/10.5772/INTECHOPEN.75987","url":null,"abstract":"The time-dependent rheological behavior of the thixotropic fluids is presented in various industrial fields (cosmetics, food, oil, etc.). Usually, a couple of equations define constitutive model for thixotropic substances: a constitutive equation based on linear viscoelastic models and a rate equation (an equation related to the micro-structural evolution of the substance). Many constitutive models do not take into account the micro-structural dependence of the shear modulus and viscosity in the dynamic principles from which are developed. The modified Jeffreys model (con-sidering only one single micro-structure type) does not show this incoherence in its formulation. In this chapter, a constitutive model for thixotropic fluids, based on modified Jeffreys model, is presented with the addition of one more micro-structure type, besides of comments on some possible generalizations. The rheological coherence of this constitutive model and thermodynamic consistency are analyzed too. This model takes into account a simple isothermal laminar shear flows, and the micro-structures dynamics are relate to Brownian motion and de Gennes Reptation model via the Smoluchowski ™ s coagulation theory.","PeriodicalId":351650,"journal":{"name":"Selected Problems of Contemporary Thermomechanics","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128078777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-10-10DOI: 10.5772/INTECHOPEN.79945
J. Winczek
Thermomechanics is a scientific discipline which investigates the behavior of bodies (solid, liquid, and gas) under the action forces and heat input. Thermomechanical phenomena commonly occur in the human environment, from the action of solar radiation to the technological processes. The analysis of these phenomena often requires extensive interdisciplinary knowledge, e.g., thermodynamics, continuum mechanics (solid and fluid), soil mechanics, biomechanics, metallurgy, hydraulics, civil engineering, and materials science and even anatomy, chemistry, meteorology, or hydrology. The wide range of thermomechanics applications depends on the field of science and the areas of knowledge in which phenomena are considered. The description of these phenomena requires not only knowledge of the laws of physics but the use of advanced mathematical apparatus, tensor algebra, and methods for solving differential and integral equations. Thermomechanical phenomena are analyzed using analytical and numerical methods. The analytical solution offers a quicker assessment of the searched values and its dependence on the various parameters, but for more complex problems, they are difficult or even impossible to apply. Some problems can be solved only with numerical methods, of which the finite element method is commonly used, but also methods of boundary elements, finite differences and elementary balances. In addition to the mentioned above methods, one needs to know how to solve complex equation systems (in case of the author’s original software) or to possess the ability to handle professional engineer’s packages. Thermomechanics therefore describes a broad category of phenomena. It is a generalization of classical mechanical theory and thermodynamic theory. Currently, thermomechanical coupling is a fully formed issue. Basic dependences and differential equations have been formulated based on mechanical and thermodynamic laws. Numerous methods and algorithms for solving differential equations of thermomechanical coupling have been developed, including the finite element method. Looking at the development of thermomechanics, we cannot omit scientists who laid the foundation for this area of science. First and foremost, Isaak Newton, the author of the three principles of dynamics [1], an outstanding physicist and mathematician, parallels with G.W. Leibniz who developed the theory of differential and integral calculus. In turn, the development of thermomechanics (and not only) was contributed by Fourier, the creator of the Fourier transform and Fourier series theories, which he used in his fundamental work on the theory of heat conduction [2]. One should also mention eminent scientists, the creator of the law of thermal radiation, Kirchhoff [3] and Maxwell [4, 5]. Over the past half-century, a number of
{"title":"Introductory Chapter: Introduction to Thermomechanics Problems","authors":"J. Winczek","doi":"10.5772/INTECHOPEN.79945","DOIUrl":"https://doi.org/10.5772/INTECHOPEN.79945","url":null,"abstract":"Thermomechanics is a scientific discipline which investigates the behavior of bodies (solid, liquid, and gas) under the action forces and heat input. Thermomechanical phenomena commonly occur in the human environment, from the action of solar radiation to the technological processes. The analysis of these phenomena often requires extensive interdisciplinary knowledge, e.g., thermodynamics, continuum mechanics (solid and fluid), soil mechanics, biomechanics, metallurgy, hydraulics, civil engineering, and materials science and even anatomy, chemistry, meteorology, or hydrology. The wide range of thermomechanics applications depends on the field of science and the areas of knowledge in which phenomena are considered. The description of these phenomena requires not only knowledge of the laws of physics but the use of advanced mathematical apparatus, tensor algebra, and methods for solving differential and integral equations. Thermomechanical phenomena are analyzed using analytical and numerical methods. The analytical solution offers a quicker assessment of the searched values and its dependence on the various parameters, but for more complex problems, they are difficult or even impossible to apply. Some problems can be solved only with numerical methods, of which the finite element method is commonly used, but also methods of boundary elements, finite differences and elementary balances. In addition to the mentioned above methods, one needs to know how to solve complex equation systems (in case of the author’s original software) or to possess the ability to handle professional engineer’s packages. Thermomechanics therefore describes a broad category of phenomena. It is a generalization of classical mechanical theory and thermodynamic theory. Currently, thermomechanical coupling is a fully formed issue. Basic dependences and differential equations have been formulated based on mechanical and thermodynamic laws. Numerous methods and algorithms for solving differential equations of thermomechanical coupling have been developed, including the finite element method. Looking at the development of thermomechanics, we cannot omit scientists who laid the foundation for this area of science. First and foremost, Isaak Newton, the author of the three principles of dynamics [1], an outstanding physicist and mathematician, parallels with G.W. Leibniz who developed the theory of differential and integral calculus. In turn, the development of thermomechanics (and not only) was contributed by Fourier, the creator of the Fourier transform and Fourier series theories, which he used in his fundamental work on the theory of heat conduction [2]. One should also mention eminent scientists, the creator of the law of thermal radiation, Kirchhoff [3] and Maxwell [4, 5]. Over the past half-century, a number of","PeriodicalId":351650,"journal":{"name":"Selected Problems of Contemporary Thermomechanics","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127850477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-10-10DOI: 10.5772/INTECHOPEN.75876
M. Banaszkiewicz, J. Badur
This chapter presents two practical methods of thermoelastic stress calculation suitable for application in online monitoring systems of steam turbines. Both methods are based on the Green function and Duhamel integral and consider the effect of variable heat transfer coefficient and material physical properties on thermal stresses. This effect is taken into account either by using an equivalent steam temperature determined with a constant heat transfer coefficient or by applying an equivalent Green ’ s function determined with variable heat transfer coefficient and physical properties. The effectiveness of both methods was shown by comparing their predictions with the results of exact three-dimensional (3D) calculations of a steam turbine valve.
{"title":"Practical Methods for Online Calculation of Thermoelastic Stresses in Steam Turbine Components","authors":"M. Banaszkiewicz, J. Badur","doi":"10.5772/INTECHOPEN.75876","DOIUrl":"https://doi.org/10.5772/INTECHOPEN.75876","url":null,"abstract":"This chapter presents two practical methods of thermoelastic stress calculation suitable for application in online monitoring systems of steam turbines. Both methods are based on the Green function and Duhamel integral and consider the effect of variable heat transfer coefficient and material physical properties on thermal stresses. This effect is taken into account either by using an equivalent steam temperature determined with a constant heat transfer coefficient or by applying an equivalent Green ’ s function determined with variable heat transfer coefficient and physical properties. The effectiveness of both methods was shown by comparing their predictions with the results of exact three-dimensional (3D) calculations of a steam turbine valve.","PeriodicalId":351650,"journal":{"name":"Selected Problems of Contemporary Thermomechanics","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131000374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-02DOI: 10.5772/INTECHOPEN.76118
Sushrut Vaidya, J. Kim
The electrochemical performance of solid oxide fuel cell (SOFC) is significantly influenced by three-phase boundary (TPB) zones in the microstructure. TPB zones are locations where all three phases comprising the microstructure such as the two solid phases and the pore phase are present. Electrochemical reactions such as oxygen reduction occur near TPBs, and TPB density is believed to affect the polarization resistance of the cathode. In this regard, the effect of interface degradation under repeated thermal loading on the mechanical integrity and electrochemical performance of solid oxide fuel cell (SOFC) electrodes is studied through finite element simulations. Image-based 3-D models are used in this study, with additional interface zones at the boundaries between dissimilar solid phases. These interface zones are composed of 3-D cohesive elements of small thickness. The effect of interface degradation on mechanical integrity is studied by subjecting 50:50 LSM:YSZ wt.% cathode models to increasing levels of thermal load from room temperature (20°C) up to operating temperature (820°C). Energy quantities (e.g., strain energy and damage dissipation) for cathode models with and without cohesive interface zones are obtained through finite element analysis (FEA). These quantities are compared using energy balance concepts from fracture mechanics to gain insight into the effects of interface degradation on mechanical integrity.
{"title":"Thermomechanics of Solid Oxide Fuel Cell Electrode Microstructures Using Finite Element Methods: Progressive Interface Degradation under Thermal Cycling","authors":"Sushrut Vaidya, J. Kim","doi":"10.5772/INTECHOPEN.76118","DOIUrl":"https://doi.org/10.5772/INTECHOPEN.76118","url":null,"abstract":"The electrochemical performance of solid oxide fuel cell (SOFC) is significantly influenced by three-phase boundary (TPB) zones in the microstructure. TPB zones are locations where all three phases comprising the microstructure such as the two solid phases and the pore phase are present. Electrochemical reactions such as oxygen reduction occur near TPBs, and TPB density is believed to affect the polarization resistance of the cathode. In this regard, the effect of interface degradation under repeated thermal loading on the mechanical integrity and electrochemical performance of solid oxide fuel cell (SOFC) electrodes is studied through finite element simulations. Image-based 3-D models are used in this study, with additional interface zones at the boundaries between dissimilar solid phases. These interface zones are composed of 3-D cohesive elements of small thickness. The effect of interface degradation on mechanical integrity is studied by subjecting 50:50 LSM:YSZ wt.% cathode models to increasing levels of thermal load from room temperature (20°C) up to operating temperature (820°C). Energy quantities (e.g., strain energy and damage dissipation) for cathode models with and without cohesive interface zones are obtained through finite element analysis (FEA). These quantities are compared using energy balance concepts from fracture mechanics to gain insight into the effects of interface degradation on mechanical integrity.","PeriodicalId":351650,"journal":{"name":"Selected Problems of Contemporary Thermomechanics","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122094017","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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