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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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Quantification of the thermohydraulic characteristics of the flexible element using experimental data
Sochorec, Rostislav ; Kilkovský, Bohuslav (referee) ; Jegla, Zdeněk (advisor)
The diploma thesis aims to establish thermo-hydraulic properties of a flexible tube described by its Darcy friction factor and film heat transfer coefficient respectively. A flexible tube (corrugated stainless steel tube) is an easily shapeable stainless steel component used to build various piping connections, in a place of more common copper or plastic made tubes. It can also be used to build heat exchangers thanks to its signature properties. The investigated product is the one developed and manufactured by the Czech company Flexira s.r.o. and sold under the brand name xConnect System. Its thermo-hydraulic properties are established by an experiment, which is based on real utilizations by Laboratory of Energy Intensive Processes in NETME (New Technologies for Mechanical Engineering) Centre at Brno University of Technology. The investigated case is a coil-shaped element serving a purpose of a water-to-water heat exchanger. The text contains a literature survey of the chosen flexible tube and a description of a draft and development of the specific experimental test based off the established theory. The obtained results are then analysed, for the purpose of establishing a functional dependence, which can then be used to calculate a film heat transfer coefficient.
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The Effect of the Bypass Factor on Design and Geometry of the Evaporator for the Cooling Unit
Vytasil, Michal ; Rubinová, Olga (referee) ; Rubina, Aleš (advisor)
Diploma thesis focuses on effect of the bypass factor on design and geometry of the evaporator for the cooling unit of data centre. Effect of the bypass factor on individual design parameters is solved in detail. All dependendecies are captured by using graphs in which s placed a cement on that parameter. In part C, mathematical and physical solutions are demonstrated calculations and processes leading to the design of the exchanger. In the end, evaluation of the calculations is done and there is also showed possible improvements for the practise.
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Boundary Conditions in the Roll Gap during Hot and Cold Rolling
Luks, Tomáš ; Pernis,, Rudolf (referee) ; Hajduk, Daniel (referee) ; Horský, Jaroslav (advisor)
Boundary conditions in the roll gap play an important role in modelling of rolling processes. In the roll gap we can observe the following: changes of rolling pressure, changes of relative velocity, influences of oxides and lubrication, etc. When taking into account all conditions mentioned above the determination of the boundary conditions is not trivial and extensive measurements are necessary. Therefore, this thesis is dealing with design of temperature and force sensors specified for the determination of friction coefficient and heat transfer coefficient in contact. The temperature sensor with an installed thermocouple measures subsurface temperature for a given depth; and then the inverse heat conduction task is used to compute temperature and heat flux on the surface. Several temperature sensors were designed and used for measuring in pilot mill and industrial rolling mill as well. The thermal responses of different sensors were compared in the numerical simulations. The inverse calculations were tested for various rolling conditions. A durability of the sensors was also studied in industrial rolling conditions. The contact stresses in the roll gap were measured by a pin, which was in direct contact with the rolled material. The forces on the top of the pin were measured by a three-axes piezoelectric force transducer and recalculated to the contact stress and friction coefficient. The sensor was implemented in a work roll and tested when rolling aluminium and steel slab for different rolling conditions. The results were compared with the integrative force sensor ROLLSURF.
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Drivers clothing thermal resistance database for iHVAC system
Hrubanová, Kristýna ; Pokorný, Jan (referee) ; Fišer, Jan (advisor)
This diploma thesis is focused on measurement of thermal properties of clothes by thermal manikin and on application of results for prediction of thermal comfort in system iHVAC. First part of thesis is dedicated to research with relation to this topic and to definitions of main computational equations necessary for experimental measurement. The choise of method for measurement based on available standards is an important part of this thesis. The main focus of thesis lies on measuring 5 combinations of clothes at different calibration temperatures and same temperature of manikin surface. Then data are examined and also the analysis of uncertaities and repeatability is maked. According to assupmtion , the independence of value of heat transfer coefficient to ambient temperature is comfirmed and calculated heat resistance of every single clothes is compared to existing wardrobe for system iHVAC. The outcome of this thesis is specificied and completed virtual wardrobe which serves to prediction of thermal comfort in car.
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Steam turbine start-up
Jelínek, Tomáš ; Kracík, Petr (referee) ; Šnajdárek, Ladislav (advisor)
This bachelor thesis focuses on steam turbine start-up process. The first part of this thesis describes in general terms the basic practices and principles of start-up. The second part deals with the general description of thermal stress on the rotor and stator part. There is also simplified calculation of start-up duration and admissible temperature difference. The last part is a calculation of heat transfer coefficient using inverse heat transfer analysis. There is a comparison of models and measurement data of thermal stress.
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Heating and cooling systems
Pavlíček, Radek ; Vyhlídalová, Karolína (referee) ; Počinková, Marcela (advisor)
The topic of this diploma thesis is large area heating and cooling systems. Theoretical part of this thesis is focused on thermal comfort of people in interier and on theoretical calculation of heat transfer and on large area heating and cooling systems. Second part is devided to two variants. First variant is design of a heating system in kindergarden with floor heating combined with plate heating radiators. Second variant is heating system with only plate heating radiators. As source of heat is used condensing gas boiler. Part of a design is preparation of hot water. Experimental part of the thesis contains measurements of coefficient of heat transfer in floor heating and wall heating.
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Optimization of a lightweight pitched roof in order to reduce summer heat gains
Svobodová, Sylvia ; Rubina, Aleš (referee) ; Sedlák,, Vladimír (referee) ; Matějka, Libor (advisor)
The thesis deals with the topic of overheating of attic rooms during the summer period. In vast majority of family houses and apartment houses with inhabited attic spaces is the roof solved as lightweight. This kind of roof assembly is not able to sufficiently resist the summer boundary conditions and leads to increased heat gains in the interior. In this work, the attention is drawn entirely to the heat penetration through the roof. Different aspects of passive cooling were applied to the roof and the impact of each change was assessed. This concerns the color of the tiles, thermal accumulation, reflective surfaces and the ventilated air layer. The temperature and velocity profiles in the ventilated cavity were monitored and an analysis of the ventilated cavity efficiency was conducted. For individual analyses was used software – based on the principles of the Finite Element Method or the dynamic simulation software. Also other methods were employed: long-term measurement of temperatures on roof models; short-term measurement of surface temperature of various kinds of roof tiles; and laboratory measurement of reflexivity. Also the effect of insect grilles on the air flow is discussed; which was tested on a ventilator track. In this publication are explained the principles of natural convection; boundary layers and the theory of the coefficient of heat transfer. This work includes a standard of the precise calculation methodology for ventilated roofs which was developed for the purpose of creating a user-friendly guide. The results of individual analyses show, a definitely positive effect of the ventilated cavity on the heat gain reduction of attic rooms. The current technical solution of a roof ridge provides the exhaust of the water vapor from a roof assembly; but for providing ventilation for reducing heat gains is insufficient. This lead to a concept of an innovative roof ridge design which enhances the air exchange between the cavity and outdoor environment.
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Experimental and Numerical Assessment of the Heat Transfer Coeficients for Industrial Steam Turbine for Siemens Industrial Turbomachinery
Hladík, Petr ; Pospíšil, Jiří (referee) ; Hrabovský, Jozef (advisor)
The subject of this diploma thesis is experimental and numerical assessment of the heat transfer coefficients during condensation of water steam in simplified parts of an industrial steam turbine. This simplified part is a pipe with circular cross section, which is often used in simulations of processes inside the steam turbine. The first part of thesis describes theoretical basics of heat transfer during conduction, convection and condensation. The content of other chapters is description of methods used to determine heat transfer coefficient. These are: ex-perimental analysis performed on a measuring device and evaluated using finite element ana-lysis (FEA), computational fluid dynamics analysis (CFD) in ANSYS CFX and analytical calculations of heat transfer coefficients using mathematical models for condensation. Thesis is concluded by validation and comparison of obtained results.
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