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The Development of Inverse Heat Conduction Problems Focused on Very Fast Processes in Microscales
Bellerová, Hana ; Jaroš, Michal (referee) ; Dohnal, Mirko (referee) ; Raudenský, Miroslav (advisor)
The inverse heat conduction task is solved to determine boundary condition of the heat equation. This work deals with the ways how to increase the accuracy of the results obtained by solving inverse task based on the Beck sequential algorithm. The work is focused on the boundary condition changing very fast. This boundary condition is determinable with difficulty. It is shown that the placement and the type of the thermocouple play major role in accuracy of the calculation. The frequency of measuring and the discriminability of used devices also play a role as well as the setup of parameters in the inverse task. The election of mentioned parameters is described with regard to the speed of cooling. Knowledge from the theoretical part of the work is applied in the experimental part. The cooling intensity is investigated during spraying of the steel sample by water with nanoparticles Al2O3, TiO2, Fe and MWNT at three different concentrations. The experiments were carried out for three spray heights (40, 100, 160 mm), three flow rates (1, 1.5, 2 kg/min) and two types of the nozzle (full cone and solid jet). Surprisingly, the cooling intensity by using nanofluids is lower about 30% in comparison to the cooling intensity of pure water. But there was an exception. The cooling intensity of 1 wt.% of carbon nanotubes in water falling from the full cone nozzle placed in distance of 100 mm from the steel surface was higher about 174%. Finally, the reasons of the behavior of nanofluids are discussed.
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Helium Cryostat for Experimental Study of Natural Turbulent Convection
Urban, Pavel ; Jícha, Miroslav (referee) ; Rotter, Miloš (referee) ; Fedor,, Ján (referee) ; Musilová, Věra (advisor)
V disertační práci je popsán heliový kryostat s experimentální válcovou konvekční celou pro studium proudění při přirozené konvekci za velmi vysokých Rayleigho čísel Ra (až do řádu 10^15) a Nusseltových čísel Nu (až do řádu 10^4). Pracovní látkou je studené 4He, které umožňuje díky výhodným fyzikálním vlastnostem dosažení velmi vysokých hodnot čísel Ra. Návrh kryostatu je založen na koncepci lázňových NMR kryostatů s nízkým odparem kryokapalin. Ve středu kryostatu je umístěna konvekční cela o průměru 300 mm a výšce 300 mm. Celu tvoří horní a spodní dno a výměnná střední část. Tyto díly jsou spojeny rozebíratelnými přírubami těsněnými indiovým drátem. Výměnná část umožňuje snadnou modifikaci geometrie cely. Hlavní přednost kryostatu spočívá v minimálním vlivu konstrukce cely a použitých materiálů na studovanou konvekci. Cela kryostatu je navržena pro pracovní tlaky do 250 kPa.
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Development of inverse sub-domain method for boundary conditions computation of heat conduction
Hřibová, Veronika ; Klimeš, Lubomír (referee) ; Pohanka, Michal (advisor)
It is very important to develop efficient but still accurate and stable numerical methods for solving heat and mass transfer processes in many industrial applications. The thesis deals with an inverse heat conduction problem which is used to compute boundary conditions (temperatures, heat flux or heat transfer coefficient). Nowadays, two approaches are often used for inverse task - sequential estimation and whole domain estimation. The main goal of this work is to develop a new approach, the so-called sub-domain method, which emphasizes advantages just as reduce disadvantages of both methods mentioned above. This approach is then tested on generated prototypic data and on data from real experiments. All methods are compared with respect to accuracy of results as well as to computational efficiency.
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Water cooling intensity prediction for given thickness of oxide layer
Haluza, Vít ; Hrabovský, Jozef (referee) ; Pohanka, Michal (advisor)
This diploma thesis is dealing with the impact of oxide scales on heat conduction. One of the main tools that were used are numerical simulations. Heat conduction is modelled by solving partial differential equations. Regression models and artificial neural networks are used for the prediction of the influence of oxides on cooling intensity. Determination of the conditions when the cooling was intensified and comparison of individual methods of prediction are the main results of the thesis.
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High Voltage Switchgear Thermal Distribution Analysis
Bílek, Tomáš ; Rudolf, Pavel (referee) ; Hrabovský, Jozef (advisor)
Cílem této práce je analýza teplotního pole vysokonapěťového rozvaděče. Tato analýza je založena na kombinaci experimentálního měření a CFD simulace proudění vzduchu v prostoru rozvaděče. Na základě výsledků pro referenční geometrii jsou předloženy návrhy na úpravu topologie rozvaděče, které mají za cíl snížení teploty kritických komponent rozvaděče během jeho provozu. Druhá část práce je spojena s problematikou oteplení plošných spojů, jakožto hlavních zdrojů tepla v prostoru rozvaděče. Pro popis závislosti oteplení plošného spoje na jeho charakteru byla použita statistická metoda design experimentu. Výsledky z experimentálního měření jsou podpořeny konečně prvkovým modelem kontaktu spoje.
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Verification of the model for predicting the properties of the combustion process
Horsák, Jan ; Kilkovský, Bohuslav (referee) ; Jegla, Zdeněk (advisor)
This work thoroughly analyzes a previously created computational model for predicting characteristic properties of the combustion process in an experimental combustion chamber. Any found shortcomings of the original model are removed and the model is further improved prior to its application on 11 real cases of combustion tests performed at various conditions and with various fuels. Data provided by the model are confronted with the data obtained during the combustion tests and the model accuracy is evaluated, based on local heat flux along the length of the combustion chamber. Finally, the overall usefulness of the model is determined by the means of evaluating the acquired accuracy values, and further possibilities of model improvement and use are presented.
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Concept of a small nuclear reactor for the heat supply purposes
Bobčík, Marek ; Skála, Zdeněk (referee) ; Martinec, Jiří (advisor)
The objective of this diploma thesis is to assess the suitability of a small nuclear reactor for the purpose of heat supply in small towns and cities. First, all the heat demands of these towns and cities are analysed. Then, a small nuclear reactor to serve these needs is designed and a computational model for burn-up fuel is created. The thesis aims to propose a design of a new heat exchanger. Economic and environmental criteria are taken into account as well and including safety measures. The outcome of this thesis is an evaluation of the whole concept with respect to potential future implementation.
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Heat transfer surfaces design and fouling of the heat exchangers from hollow plastic fibers
Bokišová, Lenka ; Dohnal, Mirko (referee) ; Raudenský, Miroslav (advisor)
This thesis studies a possibility of using hollow fibres for construction of innovative heat exchangers. The first part introduces to the field of heat exchangers and polymers as materials suitable for formation of heat transfer surfaces. Further, the potential of hollow fibres of small diameters is outlined, including the merits, limits and proposals for improving. The significant part of the work is dedicated to the review of methods of fibres fixation and separation and review of fouling and cleaning of heat exchangers. Overviews of design possibilities which prevent fibres clustering have been made. The solutions, which are prepared for experimental research at Heat Transfer and Fluid Flow Laboratory are stated, including analysis of “curly” fibres application. The next part presents calculations for models of water – water and water – air heat exchangers and discusses influence of fibre diameter, flow velocity and the other parameters on heat characteristics. The heat transfer and fluid flow formulas using for heat exchangers of a bigger order can be employed with small changes. Furthermore, the influence of hollow fibres arrangement and distances on heat transfer is discussed.
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Analysis of proces fluid pretreatment for heat exchange purpose
Navrátil, Ondřej ; Kilkovský, Bohuslav (referee) ; Jegla, Zdeněk (advisor)
This thesis is devoted purification of a gas stream with solid and liquid particles. The problem described in the thesis is connected with a real industrial case – problem of operated waste gas incineration plant. Waste gas going to thermal incineration to flame of natural gas combustion contains solid and liquid particles. Presence of particles causes fouling of waste gas preheater. The main objective of thesis is analysis of situation and operating and space limitations and design of a suitable type of particle collector to reliable elimination of particles from waste gas before entering the gas preheater and thus to mitigation of fouling of preheater heat transfer area.
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Spent fuel storage casks thermal and physical properties investigation
Hlatký, Pavel ; Martinec, Jiří (referee) ; Šen, Hugo (advisor)
This work deals with questions of spent fuel storage casks thermal and physical properties investigation. Foundations of mathematics which are necessary for describing field of temperature are included. The work itself contains calculation methods which are split into two parts. The first one deals with simplified analytic solution and the second part solves the whole problem by the numerical computation.
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