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Výpočet tepelného odporu žebrovaného chladiče
Kyanka, Radim ; Huták, Petr (oponent) ; Toman, Marek (vedoucí práce)
Tato bakalářská práce je zaměřena na problematiku výpočtu analytických vztahů potřebných na definování tepelných odporů žebrovaných chladičů. Nejprve je popsáno, jak probíhá teplota při různých okrajových podmínkách na konci žebra. Poté popisuje mechanismy přestupu tepla, výpočty tepelných odporů obzvlášť u přirozené a nucené konvekce. Pro ověření jsou provedeny porovnání mezi výpočty pomocí analytických vztahů obsaženy v programu Matlab a výsledky z praktického měření.
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High Voltage Switchgear Thermal Distribution Analysis
Bílek, Tomáš ; Rudolf, Pavel (oponent) ; Hrabovský, Jozef (vedoucí práce)
This thesis deals with analysis of thermal field inside high voltage switchgear cabin. It de-scribes applied methodology based on combination of CFD simulation of air flow inside switch-gear cabin and series of experimental measurements. Based on results for reference geometry it provides proposals of switchgear layout modification to decrease temperature rise on switch-gear critical components during its operation. In the second part of this thesis problem of bus-bar joints is discussed. Busbar joints are one of the key thermal sources inside switchgear cab-in. Statistical method of design of experiment is applied for experimental investigation of bus-bar joint temperature rise. Results from design of experiment are supported by finite element simulation of contact in busbar joint.
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Helium Cryostat for Experimental Study of Natural Turbulent Convection
Urban, Pavel ; Jícha, Miroslav (oponent) ; Rotter, Miloš (oponent) ; Fedor,, Ján (oponent) ; Musilová, Věra (vedoucí práce)
The thesis focuses on the design of a helium cryostat with an experimental convection cell for the study of natural turbulent convection in the range of Rayleigh numbers Ra up to 1015 and Nusselt numbers Nu up to 104. Cryogenic 4He gas is used as a working fluid for experimental studies due to its advantageous properties that allow reaching very high Ra numbers. The cryostat design is based on the conception of low-loss NMR magnet cryostats. In the centre of the cryostat a cylindrical convection cell of 300 mm in diameter and 300 mm in height is placed. The cell is made of middle, top and bottom parts. These are jointed together by flanges sealed by indium wires. The middle part is exchangeable and allows the geometry of the cell to be modified. The cell is designed for measurements at pressures up to 250 kPa. The main advantage of this cryostat is the minimal influence of the cell design and materials on the studied convection.
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Polymeric Hollow Fiber Heat Exchanger Design
Astrouski, Ilya ; Dohnal, Mirko (oponent) ; Horák, Aleš (oponent) ; Raudenský, Miroslav (vedoucí práce)
This Ph.D. thesis is focused on theory and experimental investigations developing of new knowledge about polymeric hollow fiber heat exchanger (PHFHE). The state-of-the-art study of plastic heat exchangers shows that their usage is limited by several niches where their advantages significantly dominates, or where the use of non-plastic competitors is not impossible. On the other hand, plastic heat exchangers (and PHFHEs in particular) are devices of increasing interest. It is shown that use of small tubes (fibers) allows PHFHEs to be more competitive than conventional plastic heat exchangers. Small hydraulic diameter of a fiber causes high heat transfer coefficients, reduces thermal resistance of plastic wall and allows it to create light and compact design. Detailed study of fluid flow and heat transfer inside the hollow fiber showed that conventional approaches for single-phase laminar flow can be utilized. Poiseuille number equal to 64 and Nussel number about 4 are recommended to be used to predict pressure drops and heat transfer coefficient, respectively. Additional attention should be paid to careful determination of fiber diameter and liquid properties (viscosity). Scaling effects, such as axial heat conduction, thermal entrance region and viscous dissipation can be neglected. The study of outside heat transfer showed that heat transfer on fiber bunches are intense and are competitive to contemporary compact finned-tube heat exchangers. The Grimson approach showed clear correlation with experimental results and, thus is recommended to predict heat transfer coefficients on fiber bunches. Two types of fouling (particulate- and biofouling) of outer fiber surface were experimentally studied. It was found that particulate fouling by titanium oxide particles is not intense and deposits can be removed relatively easy. However, fouling is much more intense when it is associated with biofouling caused by wastewater. In this case, smooth and low-adhesive surface of plastic is not sufficient precaution to prevent deposit formation.
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Výpočet tepelného odporu žebrovaného chladiče
Kyanka, Radim ; Huták, Petr (oponent) ; Toman, Marek (vedoucí práce)
Tato bakalářská práce je zaměřena na problematiku výpočtu analytických vztahů potřebných na definování tepelných odporů žebrovaných chladičů. Nejprve je popsáno, jak probíhá teplota při různých okrajových podmínkách na konci žebra. Poté popisuje mechanismy přestupu tepla, výpočty tepelných odporů obzvlášť u přirozené a nucené konvekce. Pro ověření jsou provedeny porovnání mezi výpočty pomocí analytických vztahů obsaženy v programu Matlab a výsledky z praktického měření.
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Polymeric Hollow Fiber Heat Exchanger Design
Astrouski, Ilya ; Dohnal, Mirko (oponent) ; Horák, Aleš (oponent) ; Raudenský, Miroslav (vedoucí práce)
This Ph.D. thesis is focused on theory and experimental investigations developing of new knowledge about polymeric hollow fiber heat exchanger (PHFHE). The state-of-the-art study of plastic heat exchangers shows that their usage is limited by several niches where their advantages significantly dominates, or where the use of non-plastic competitors is not impossible. On the other hand, plastic heat exchangers (and PHFHEs in particular) are devices of increasing interest. It is shown that use of small tubes (fibers) allows PHFHEs to be more competitive than conventional plastic heat exchangers. Small hydraulic diameter of a fiber causes high heat transfer coefficients, reduces thermal resistance of plastic wall and allows it to create light and compact design. Detailed study of fluid flow and heat transfer inside the hollow fiber showed that conventional approaches for single-phase laminar flow can be utilized. Poiseuille number equal to 64 and Nussel number about 4 are recommended to be used to predict pressure drops and heat transfer coefficient, respectively. Additional attention should be paid to careful determination of fiber diameter and liquid properties (viscosity). Scaling effects, such as axial heat conduction, thermal entrance region and viscous dissipation can be neglected. The study of outside heat transfer showed that heat transfer on fiber bunches are intense and are competitive to contemporary compact finned-tube heat exchangers. The Grimson approach showed clear correlation with experimental results and, thus is recommended to predict heat transfer coefficients on fiber bunches. Two types of fouling (particulate- and biofouling) of outer fiber surface were experimentally studied. It was found that particulate fouling by titanium oxide particles is not intense and deposits can be removed relatively easy. However, fouling is much more intense when it is associated with biofouling caused by wastewater. In this case, smooth and low-adhesive surface of plastic is not sufficient precaution to prevent deposit formation.
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Helium Cryostat for Experimental Study of Natural Turbulent Convection
Urban, Pavel ; Jícha, Miroslav (oponent) ; Rotter, Miloš (oponent) ; Fedor,, Ján (oponent) ; Musilová, Věra (vedoucí práce)
The thesis focuses on the design of a helium cryostat with an experimental convection cell for the study of natural turbulent convection in the range of Rayleigh numbers Ra up to 1015 and Nusselt numbers Nu up to 104. Cryogenic 4He gas is used as a working fluid for experimental studies due to its advantageous properties that allow reaching very high Ra numbers. The cryostat design is based on the conception of low-loss NMR magnet cryostats. In the centre of the cryostat a cylindrical convection cell of 300 mm in diameter and 300 mm in height is placed. The cell is made of middle, top and bottom parts. These are jointed together by flanges sealed by indium wires. The middle part is exchangeable and allows the geometry of the cell to be modified. The cell is designed for measurements at pressures up to 250 kPa. The main advantage of this cryostat is the minimal influence of the cell design and materials on the studied convection.
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High Voltage Switchgear Thermal Distribution Analysis
Bílek, Tomáš ; Rudolf, Pavel (oponent) ; Hrabovský, Jozef (vedoucí práce)
This thesis deals with analysis of thermal field inside high voltage switchgear cabin. It de-scribes applied methodology based on combination of CFD simulation of air flow inside switch-gear cabin and series of experimental measurements. Based on results for reference geometry it provides proposals of switchgear layout modification to decrease temperature rise on switch-gear critical components during its operation. In the second part of this thesis problem of bus-bar joints is discussed. Busbar joints are one of the key thermal sources inside switchgear cab-in. Statistical method of design of experiment is applied for experimental investigation of bus-bar joint temperature rise. Results from design of experiment are supported by finite element simulation of contact in busbar joint.
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Charakter proudění v náplňovém superkritickém extraktoru
Rochová, Kristina ; Sovová, Helena
Příspěvek obsahuje nejprve krátký přehled literatury týkající se vlivu směru proudění rozpouštědla na průběh superkritické extrakce. Dále jsou shrnuty první výsledky měření axiální disperze během extrakce, což je problematika, která nebyla zatím v literatuře dostatečně popsána. Charakter proudění byl studován metodou sledování odezvy na stopovací látku, výsledky byly vyjádřeny ve formě bezrozměrné variance píku odezvy. Jako extrahovaná látka byl použit tetrakosan, nanesený na inertní skleněné kuličky. Bylo zjištěno, že při toku rozpouštědla proti směru gravitace je charakter proudění výrazněji ovlivněn přirozenou konvekcí v extraktoru, nežli je tomu při toku ve směru gravitace.
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