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EFFECT OF FLOW PARAMETERS OF WATER AND AIR ATOMIZED SPRAYS ON COOLING INTENSITY OF HOT SURFACES
Boháček, Jan ; Střasák,, Pavel (oponent) ; Rudolf, Pavel (oponent) ; Horský, Jaroslav (vedoucí práce)
The present thesis is focused on an overall description of water jets and air atomized jets for cooling purposes using CFD methods namely ANSYS FLUENT. It comprises two main parts – the micro and the macro model. The micro model concerns with a numerical description of single droplet dynamics whereas the macro model deals with a numerical modeling of water jets as complicated droplet structures emanating from solid stream nozzle and flat fan nozzle. By and large, it is based on multiphase models and User Defined Functions (UDFs), which represents the background of the present thesis. In most of cases, the presented numerical models were compared either with experimental data or another numerical model. In the first part, the theory of each of three multiphase models is discussed. The first one, the Volume Of Fluid model (VOF), was used for simulation of single droplet dynamics designated as a micro model whilst last two multiphase models, the Euler-Euler model and the Euler-Lagrange model, were applied in the case of modeling of the entire water jet structure, which is contrarily designated as a macro model. The micro model concerns with a numerical study of free-falling water droplet. For small droplet diameters (~100µm) the standard surface tension model (Continuum Surface Force model, CSF) was proved to cause significant unphysical parasitic currents. Therefore, the thesis is also devoted to surface tension as a source term of body forces imposed in momentum equation, normal, curvature calculation and related issues. The macro model covers a numerical study of dynamics of the entire water jet structure i.e. the space between the nozzle exit and the wall where the jet impinges. It accounts for the complete geometry, for instance, support rolls, a slab and a mold bottom of a continuous caster. Firstly, the physics of a solid jet impact onto a hot plate was simulated using both, the VOF and the Euler-Lagrange model. As regards the case with the VOF model, a model for film boiling was designed and tested. Finally, both, the Euler-Euler model and the Euler-Lagrange model, were used for simulation of a flat jet horizontally spraying onto a hot slab inside a confined domain bounded by support rolls and a mold bottom. Concerning the simulation with the Euler-Euler model, a secondary breakup model was introduced based on the wave stability atomization theory. Concerning the Euler-Lagrange simulation, the dispersed phase (Lagrange particles) formed rather a continuous phase in some places, and therefore the coupling between Lagrange particles and the VOF model via UDFs was proposed.
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Computational modeling of heat transfer problems in porous structures
Mráz, Kryštof ; Karimi-Sibaki, Ebrahim (oponent) ; Boháček, Jan (vedoucí práce)
The scale layer, consisting of porous iron oxides, formed on the steel surface during the heat treatment has a great impact on thermal metallurgical processes. The thermal conductivity of a scale is one of the key parameters for the numerical modeling of the steel cooling and descaling. However, the conductivity is highly influenced by the scale porous structure and at the present time no generally accepted material data exist. The goal of this thesis was to perform a thermal steady-state analysis to determine the thermal conductivity of the scale. A detailed 3D FE model of the scale layer based on a data acquired by CT scanning was created. The CT image acquisition and image processing are described. Two distinct segmentation approaches were implemented. A cubic uniform computational mesh was generated from the voxel matrix of the processed CT image. Performed FE analyses resulted into nearly same values of the scale thermal conductivity for both segmentation approaches, which indicates their correctness. The resulting thermal conductivity of the scale could be used as a material property in further numerical models of the heat treatment of a steel.
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Spor města Turnova s Valdštejny na počátku 18. století. Příspěvek ke studiu poddansko-vrchnostenských vztahů
Boháček, Jan ; Maur, Eduard (vedoucí práce) ; Čechura, Jaroslav (oponent)
Poměr mezi poddanými a vrchnostmi lze dobře sledovat v období vzájemných konfliktů. Tehdy musela být artikulována sporná témata a konfliktní oblasti, otevřený spor také zanechal výraznější stopu v písemných pramenech. K poddansko-vrchnostenským sporům ve vesnickém prostředí existuje již rozsáhlá odborná literatura. Značná pozornost se soustředila na výzkum nevolnických povstání v 17. a 18. století. Naproti tomu problematice vztahu poddanských měst s jejich vrchnostmi v pobělohorském období bylo u nás věnováno dosud jen málo pozornosti. Překážku tvoří především individualizované poměry v jednotlivých městech, komplikovanější sociální struktura městských obcí ve srovnání s venkovem a v neposlední řadě množství pramenů, dosud jen nedostatečně zpracovaných.
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Computational modeling of heat transfer problems in porous structures
Mráz, Kryštof ; Karimi-Sibaki, Ebrahim (oponent) ; Boháček, Jan (vedoucí práce)
The scale layer, consisting of porous iron oxides, formed on the steel surface during the heat treatment has a great impact on thermal metallurgical processes. The thermal conductivity of a scale is one of the key parameters for the numerical modeling of the steel cooling and descaling. However, the conductivity is highly influenced by the scale porous structure and at the present time no generally accepted material data exist. The goal of this thesis was to perform a thermal steady-state analysis to determine the thermal conductivity of the scale. A detailed 3D FE model of the scale layer based on a data acquired by CT scanning was created. The CT image acquisition and image processing are described. Two distinct segmentation approaches were implemented. A cubic uniform computational mesh was generated from the voxel matrix of the processed CT image. Performed FE analyses resulted into nearly same values of the scale thermal conductivity for both segmentation approaches, which indicates their correctness. The resulting thermal conductivity of the scale could be used as a material property in further numerical models of the heat treatment of a steel.
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Spor města Turnova s Valdštejny na počátku 18. století. Příspěvek ke studiu poddansko-vrchnostenských vztahů
Boháček, Jan ; Čechura, Jaroslav (oponent) ; Maur, Eduard (vedoucí práce)
Poměr mezi poddanými a vrchnostmi lze dobře sledovat v období vzájemných konfliktů. Tehdy musela být artikulována sporná témata a konfliktní oblasti, otevřený spor také zanechal výraznější stopu v písemných pramenech. K poddansko-vrchnostenským sporům ve vesnickém prostředí existuje již rozsáhlá odborná literatura. Značná pozornost se soustředila na výzkum nevolnických povstání v 17. a 18. století. Naproti tomu problematice vztahu poddanských měst s jejich vrchnostmi v pobělohorském období bylo u nás věnováno dosud jen málo pozornosti. Překážku tvoří především individualizované poměry v jednotlivých městech, komplikovanější sociální struktura městských obcí ve srovnání s venkovem a v neposlední řadě množství pramenů, dosud jen nedostatečně zpracovaných.
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EFFECT OF FLOW PARAMETERS OF WATER AND AIR ATOMIZED SPRAYS ON COOLING INTENSITY OF HOT SURFACES
Boháček, Jan ; Střasák,, Pavel (oponent) ; Rudolf, Pavel (oponent) ; Horský, Jaroslav (vedoucí práce)
The present thesis is focused on an overall description of water jets and air atomized jets for cooling purposes using CFD methods namely ANSYS FLUENT. It comprises two main parts – the micro and the macro model. The micro model concerns with a numerical description of single droplet dynamics whereas the macro model deals with a numerical modeling of water jets as complicated droplet structures emanating from solid stream nozzle and flat fan nozzle. By and large, it is based on multiphase models and User Defined Functions (UDFs), which represents the background of the present thesis. In most of cases, the presented numerical models were compared either with experimental data or another numerical model. In the first part, the theory of each of three multiphase models is discussed. The first one, the Volume Of Fluid model (VOF), was used for simulation of single droplet dynamics designated as a micro model whilst last two multiphase models, the Euler-Euler model and the Euler-Lagrange model, were applied in the case of modeling of the entire water jet structure, which is contrarily designated as a macro model. The micro model concerns with a numerical study of free-falling water droplet. For small droplet diameters (~100µm) the standard surface tension model (Continuum Surface Force model, CSF) was proved to cause significant unphysical parasitic currents. Therefore, the thesis is also devoted to surface tension as a source term of body forces imposed in momentum equation, normal, curvature calculation and related issues. The macro model covers a numerical study of dynamics of the entire water jet structure i.e. the space between the nozzle exit and the wall where the jet impinges. It accounts for the complete geometry, for instance, support rolls, a slab and a mold bottom of a continuous caster. Firstly, the physics of a solid jet impact onto a hot plate was simulated using both, the VOF and the Euler-Lagrange model. As regards the case with the VOF model, a model for film boiling was designed and tested. Finally, both, the Euler-Euler model and the Euler-Lagrange model, were used for simulation of a flat jet horizontally spraying onto a hot slab inside a confined domain bounded by support rolls and a mold bottom. Concerning the simulation with the Euler-Euler model, a secondary breakup model was introduced based on the wave stability atomization theory. Concerning the Euler-Lagrange simulation, the dispersed phase (Lagrange particles) formed rather a continuous phase in some places, and therefore the coupling between Lagrange particles and the VOF model via UDFs was proposed.
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