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The finite element method for problems of heat transfer
Čupr, Pavel ; Chabičovský, Martin (referee) ; Štětina, Josef (advisor)
The study is focused on the research of heat transfer problems when assessing building constructions. It contains an overview of heat transfer theory, basic principles of method of advanced composites (MAC) and an outline of currently available MAC programmes based on open code. It researches the building constructions in terms of the heat transfer. The assignment uses analytical and numerical modelling of Ansys programme. Finally, acquired results have been compared and building constructions have been studied with regard to acceptability of different sets of temperatures.
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Acceleration of numerical computation of heat conduction in solids in inverse tasks
Ondruch, Tomáš ; Komínek, Jan (referee) ; Pohanka, Michal (advisor)
The master's thesis deals with possible ways of accelerating numerical computations, which are present in problems related to heat conduction in solids. The thesis summarizes basic characteristics of heat transfer phenomena with emphasis on heat conduction. Theoretical principles of control volume method are utilized to convert a direct heat conduction problem into a sparse linear system. Relevant fundamentals from the field of inverse heat conduction problems are presented with reference to intensive computations of direct problems of such kind. Numerical methods which are well-suited to find a solution of direct heat conduction problems are described. Remarks on practical implementation of time-efficient computations are made in relation with a two-dimensional heat conduction model. The results are compared and discussed with respect to obtained computational time for several tested methods.
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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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Indirect air heating
Beneš, Josef ; Adam, Pavel (referee) ; Počinková, Marcela (advisor)
The master Thesis deals with indirect air heating in air handling units. In the theoretical part of the thesis the categories of heat exchangers are defined according to their positioning in ventilation system, used material and type of heat transfer fluid. To the issue of calculating heat exchanges through heat exchangers and description of different kinds of regulation of primary heat transfer fluid is dedicated a separate chapter. The experimental part of the thesis deals with determining performance of current air heat exchanger at set thermal gradient with various heat transfer fluids. In the calculating part of the Thesis, based on measured values, are suggested two possible solutions for use of technological waste heat. Final evaluation of particular solutions was based on the criterion of efficiency usage and implementation investment costs.
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Method for the solution of conduction heat transfer in Phase change material with nanoparticles
Kopečková, Barbora ; Knotek, Stanislav (referee) ; Jícha, Miroslav (advisor)
This master thesis deals with problematic of the heat convection in phase change materials (PCM) and PCM with nanoparticles. The derivation of stationary and non-stationary equations for 1D, 2D and 3D heat convection are described in detail. The finite element volume method is used for solution to these equations, of which principle is described carefully. The aim of this thesis is model development for 2D solution to temperature distribution at heat convection in PCM and influence assessment of nanoparticle implementation into material on given temperature distribution. Software MATLAB was used for model development, solution and plotting graphs.
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Flow sensor
Symerský, Tomáš ; Psota, Boleslav (referee) ; Kosina, Petr (advisor)
This diploma thesis is divided into two parts - theoretical and practical. In its first, theoretical part, deals with the theory of fluid and gas flow, heat transfer and diversification of sensors for flow measurement working on the electrical principle. It also deals with thermodynamic principle, which can be used for measuring very small flow and low-temperature ceramics that is used to implement microcanals for sensing very low flows. The practical part of the thesis deals with the very simulation of the entire structure in the program “COMSOL Multiphysics” - both in 2D and 3D views. Then there is shown the implementation and measurement of the flow sensor in a low-temperature ceramics, working on a thermodynamic principle.
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Thermal Contact Resistance Under High Temperature
Kvapil, Jiří ; Návrat, Tomáš (referee) ; Brestovič, Tomáš (referee) ; Horský, Jaroslav (advisor)
Nowadays numerical simulations are used to optimize manufacturing process. These numerical simulations need a large amount of input parameters and some of these parameters have not been sufficiently described. One of this parameter is thermal contact resistance, which is not sufficiently described for high temperatures and high contact pressure. This work describes experimental measuring of thermal contact resistance and how to determine thermal contact conductance which can be used as a boundary condition for numerical simulations. An Experimental device was built in Heat Transfer and Fluid Flow Laboratory, part of Brno University of Technology, and can be used for measuring thermal contact conductance in various conditions, such as contact pressure, initial temperatures of bodies in contact, type of material, surface roughness, presence of scales on the contact surface. Bodies in contact are marked as a sensor and a sample, both are embedded with thermocouples. The temperature history of bodies during an experiment is measured by thermocouples and then used to estimate time dependent values of thermal contact conductance by an inverse heat conduction calculation. Results are summarized and the dependence of thermal contact conductance in various conditions is described.
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Selection of suitable fluid flow directions in laminar flow tubular cooler
Krobot, David ; Kohoutek, Josef (referee) ; Jegla, Zdeněk (advisor)
This master’s thesis is devoted to problematic of selection of suitable flow directions in double pipe heat exchanger. First chapter is oriented to the construction of tube heat exchangers. It is also discussed impact of construction solution to the flow character and changing of his process parameters. The difference between parallel and countercurrent flow is also occurred in this parts. The next chapter is focused to the basics of heat-hydraulic calculations of heat exchanger. This also means explanation of ways of heat transfer and heat exchanger function. There are told about specific access to the solving problem of fluid laminar flow. The third chapter is detailed focused to the calculating of heat exchanger. At first is discussed factors, which have impact to the flow character. Next are detailed descriptions of design and controlling calculations, including more alternative ways to solve it. Next chapter exploit those results for deciding, which flow arrangement will be better for given case. Last chapter contain realization and reformulating of process heat exchanger calculating to the program code in Maple. There is also description of used algorithms and operating with them, so any user could be able to work with it. In this master’s thesis are used many examples from attached programs on different parts.
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Model predictive Control for continuous casting of steel
Zemanová, Hana ; Mauder, Tomáš (referee) ; Štětina, Josef (advisor)
In this thesis an equation of heat conduction including phase and structural changes is derived, involving various boundary conditions. It seems to be the most suitable to calculate the equation by enthalpy method. In this equation not only enthalpy occurs, but also the temperature, and in consequence the relationship between these variables is quite complicated. In this paper I use the values measured or calculated using solidifcation models. The calculation is implemented in Matlab Simulink, which is a very popular blocks scheme in common practice of regulation. The calculation is based on steady state set up with help of experts and as a result, the program could be put into practice. The program calculates the intensity of cooling according to the initial casting speed, casting inlet temperature and the desired temperature curves. The rate of inuence of cooling can be changed according to the given criteria. The thesis compares the surface temperatures and cooling in the case of a predictive controller is or is not applied in the program.
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Design of optimal parameters of multilayer ceramic protective coating for high temperature applications
Dohnalík, Petr ; Hrstka, Miroslav (referee) ; Ševeček, Oldřich (advisor)
The main objective of this work was to design a suitable composition of a protective coatings, made of several different layers of specific materials - with respect to residual stress, induced due to a mismatch in thermal expansion coefficients of each layer. Protective coating in this work means both the thermal and the environmental barrier. These coatings protect components against high temperatures and harsh environment. In this work, necessary theoretical background in the field of the thermal and environmental barrier coatings is introduced. There are mentioned some basic design approaches, commonly used materials and processing methods for the coating structure. The literature review gives an overview of modeling of such coated structures, in particular it is devoted to the thermal barrier coatings deposited by air plasma spray process. The next chapter closely describes classical laminate theory used for calculation of residual stresses in the coating. One of the assumptions of this theory is homogenous temperature field through the coating’s thickness. However, in this work was revealed a way to extend the classical lamination theory of such cases, in which the temperatures vary along the thickness of the coating. In the practical part, the analytical model was used for designing suitable properties of some coatings, which were consists of two, three and four layers. The calculations were performed both for constant temperature and for the temperature gradient. All results obtained from analytical approach were verified by numerical calculations.
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