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Heat transfer in the tubular exchangers
Horvát, Petr ; Krištof, Ondřej (referee) ; Svěrák, Tomáš (advisor)
Shell and tube heat exchangers and their use in cooling processes are the major topic of this thesis. The theoretical part of the thesis starts with the mechanisms of heat transfer and then deals with shell and tube heat exchangers. Their position, design specifications and equations for calculations are given. In the experimental part, the heat transfer on semi-operating shell and tube heat exchangers with baffles and glass or silicon carbide heat exchange surface is examined by cooling the humid air by 50% propylene glycol in tubes. For four or five coolant flows and three airflows, input and output flow temperatures including relative air humidity were measured. Differences in exchanged heat between the exchangers were negligible due to the low local air heat transfer coefficient, although silicon carbide has two orders of magnitude better thermal conductivity than glass. Much higher efficiency was performed by the carbide heat exchanger because the difference between air outlet temperature and liquid inlet temperature was one and half times higher for the glass heat exchanger. That was reflected in a decrease in mean temperature difference, which resulted in a 16 % higher experimental heat transfer coefficient compared with the glass surface. The theoretical model using the j factor, the correction factors for the baffles, and the correction for air humidity condensation have proven to be appropriate. For the glass surface, for the highest air flow rates the model gives an appropriate heat-transfer coefficient; at lower flow rates it gives slightly higher values. For the silicon carbide surface, it gives a lower heat-transfer coefficient because the model failed to consider a lower mean temperature difference. The results also evaluate the heat loss through the shell and the heat exchanged in addition by air humidity condensation.
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Influence of Bottom Preheating in Rework of Assembled PCB
Čechák, Ondřej ; Bžoněk, Tomáš (referee) ; Starý, Jiří (advisor)
This bachelor's thesis introduces the problematics of physical mechanisms of heat transfer and the correlative mathematical formulas and the use of mentioned problematics in the technology of bottom preheating in the rework of assembled printed circuit boards. It explains the importance and reasons of use of this technology, not merely in the professional production. It focuses on expert analysis of the appliances based on their properties and clarifies the differences in basic types of the devices. The emphasis is then laid on a practical testing of the technical parameters of the preheating devices as well as on an experimental design and a practical testing of a local bottom printed circuit board preheater.
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New Elements of Heat Transfer Efficiency Improvement in Systems and Units
Turek, Vojtěch ; Klemeš,, Jiří (referee) ; Odstrčil, Miloslav (referee) ; Jegla, Zdeněk (advisor)
Zvýšení efektivity výměny tepla vede k poklesu spotřeby energie, což se následně projeví sníženými provozními náklady, poklesem produkce emisí a potažmo také snížením dopadu na životní prostředí. Běžné způsoby zefektivňování přenosu tepla jako např. přidání žeber či vestaveb do trubek ovšem nemusí být vždy vhodné nebo proveditelné -- zvláště při rekuperaci tepla z proudů s vysokou zanášivostí. Jelikož intenzita přestupu tepla závisí i na charakteru proudění, distribuci toku a zanášení, které lze všechny výrazně ovlivnit tvarem jednotlivých součástí distribučního systému, bylo sestaveno několik zjednodušených modelů pro rychlou a dostatečně přesnou predikci distribuce a také aplikace pro tvarovou optimalizaci distribučních systémů využívající právě tyto modely. Přesnost jednoho z modelů byla dále zvýšena pomocí dat získaných analýzou 282 distribučních systémů v softwaru ANSYS FLUENT. Vytvořené aplikace pak lze využít během návrhu zařízení na výměnu tepla ke zvýšení jejich výkonu a spolehlivosti.
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Modeling of the thermal effects on living tissue during electroporation process
Kafka, Roman ; Cipín, Radoslav (referee) ; Červinka, Dalibor (advisor)
The work deals with the current state of knowledge of heat transfer in living tissue. It is described here what the distribution of heat is affected with and the existing calculation options. For solving Pennes equation using finite element method COMSOL Multiphysics 5.4 is used. From the current state of the published studies, three are selected and described, each using a different approach. Based on the benefit of each of the studies described, a simple model of its own that simulates an ablation catheter attached to cardiac tissue is solved. A change in electrical conductivity as a function of the electric field intensity is taken into account, but there is also a comparison with anisotropic tissue that has electrical conductivity in different directions. The result of the calculation is voltage distribution, density of electric current and losses, temperature distribution in the model at several time points and graph of temperature development over time.
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Mathematical description of dynamic heat exchanger
Hvožďa, Jiří ; Hnízdil, Milan (referee) ; Kůdelová, Tereza (advisor)
This bachelor's thesis deals with an analysis of a dynamic heat exchanger, with neglect to position, described by the system of ordinary differential equations. It includes necessarily theoretical basis of ordinary differential eqations and thermomechanics, a study of ordinary differential eqations' solution existence, overview of types of heat exchangers according to various aspects.
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Thermo-physical parameters of exo-sleeves and their application in simulation programmes
Zajíček, Roman ; Kuzma, Zbyněk (referee) ; Roučka, Jaromír (advisor)
Thesis discusses exothermic sleeves. The first chapter briefly described the defects can occur during solidification. Further, there are provided methods for removing these defects. The method is described in detail using risers with an emphasis on the exothermic sleeves and thermo-physical parameters characterizing these sleeves. It also describes the influence of these parameters on the accuracy of computer simulations. In the final part of the work is done measuring of the real casting, which is then simulated in the Quikcast.
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Combination of numerical mathematics and neural network for the model of breakout prediction
Srba, Jan ; Štětina, Josef (referee) ; Mauder, Tomáš (advisor)
This thesis deals with creation of breakout prediction model implemented via artificial neural network in MATLAB, hence it contains theoretical description of artificial neural networks and also presents how the networks were used for the breakout prediction problem. In addition, models of heat conduction through the mold wall were created and used for generating neccesary data for proper training of artificial neural network. The thesis contains proper description of used numerical methods for solving the heat conduction problems. In the thesis are presented partial results and also results of testing created artificial neural network with usage of real data.
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