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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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Design of Experiment for Inverse Heat Transfer Problem
Horák, Aleš ; Pavliska,, Martin (referee) ; Štětina, Josef (referee) ; Raudenský, Miroslav (advisor)
this thesis complex inverse heat transfer problem, which is focused on optimal design of experiment, is studied. There are many fields and applications in technical practice, where inverse tasks are or can be applied. On first place main attention is focused on industrial metallurgical processes such as cooling of continues casting, hydraulic descaling or hot rolling. Inverse problems are in general used to calculate boundary conditions of differential equations and in this field are used to find out Heat Transfer Coefficient (HTC). Knowledge of numerical approximation of precise boundary conditions is nowadays essential. It allows for example design of optimized hot rolling mill cooling focused on material properties and final product quality. Sequential Beck’s approach and optimization method is used in this work to solve inverse heat transfer problems. Special experimental test bench measuring heat transfer intensity was developed and built to full fill specific requirements and required accuracy. There were four different types of thermal sensor applied and studied. Those sensors are in usage in Heat Transfer and Fluid Flow laboratory (Heatlab) at various experimental test benches. Each specific sensor was tailored in Heat Transfer and Fluid Flow Laboratory to specific metallurgical application. Fist type of sensor was designed to simulate cooling during continuous casting. Second sensor is used for experiments simulate hot rolling mill cooling, while third sensor is designated for experiments with fast moving hot rolled products. Last sensor is similar to sensor type one, but thermocouple is located parallel to cooled surface. Experimental part of this study covers series of measurements to investigate Heat Transfer Coefficient (HTC) for various types of coolant, cooling mixtures and spray parameters. Results discovered in this study were compared with published scientific articles, and widely extend the knowledge of cooling efficiency for commonly used
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Polymeric Hollow Fiber Heat Exchanger Design
Astrouski, Ilya ; Dohnal, Mirko (referee) ; Horák, Aleš (referee) ; Raudenský, Miroslav (advisor)
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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Developement of In-Line Heat Treatment Methods
Hnízdil, Milan ; Štětina, Josef (referee) ; Pospíchal, Miroslav (referee) ; Raudenský, Miroslav (advisor)
In-line heat treatment is a part of technological process uses a phase and structure changes to obtain required mechanical properties. Heat treatment of rolled products offers a reduction of steel making costs and a creation of new steel products. For example the TRIP steel is a part of modern steels which is used in the automobile industry for higher safety of passengers. The heat treatment is often described in the literature. But the authors are often focused on the method how to get the required structure and mechanical properties for different metallic materials. Nevertheless just few articles are focused on the technical observing of temperature regimes and which parameter is necessary to consider during designing the cooling section. Eight parameters were tested by the experimental way to examine their influence on the cooling intensity. They were: gravity (orientation of the cooled surface), coolant pressure, amount of coolant spraying on the surface (the flow rate), rolling velocity, nozzle configuration, kind of nozzles (full cone or flat fan nozzle), coolant temperature and the surface quality (surface roughness and scales). All these parameters have an influence the heat transfer coefficient. Based on knowledge gained in this work was created the cooling section, which comply with the required cooling temperature regimes.
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Design of a fleet of single-pilot airplanes used for air taxi around Europe
Klačan, Matej ; Raudenský, Miroslav (referee) ; Imriš, Pavel (advisor)
The aim of this thesis is to provide a comprehensive overview and analysis of the issue for entrepreneurs who are interested in starting a business in private air transport within Europe with a fleet of single-pilot aircraft. By examining the latest trends and developments in the European market in this sector, the thesis offers valuable insights into current preferences and can serve as a basis for predictions. The study includes a thorough market analysis of currently produced single-pilot airplanes suitable for commercial transport in Europe. In addition, the work examines the current demand for private air transport in Europe, using market research to identify potential opportunities and challenges. In addition, after considering financial aspects, and analysis of fixed and variable costs, this work provides entrepreneurs with a rough estimate of the financial investment required to start and maintain their business.
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Planning of optimal VFR routes from the Czech Republic to the Republic of Croatia
Klačan, Matej ; Raudenský, Miroslav (referee) ; Sklenář, Filip (advisor)
The aim of this bachelor thesis is to create a detailed ground preparation of three different VFR flights from Czech Republic to the Republic of Croatia for a full occupied Cessna 172SP. The first reserch part is general introduction to the issue and acquaintance with the aircraft and its equipment. Special emphasis is placed on the fact that all planed flights are in accordance with aviation legislation, which is dealt with in the second part of the research part of the thesis work. The practical part of the thesis work deals with the issue of ground preparation itself, with the fact that it deals in more detail with navigation preparation of individual flights. Finally, the financial demands for our flights are given.
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Optimization of Heat Transfer Surfaces of Heat Exchangers
Bartuli, Erik ; Dohnal, Mirko (referee) ; Vinogradov, Andrey Vladimirovich (referee) ; Raudenský, Miroslav (advisor)
Disertační práce je zaměřena na kovové a polymerní výměníky tepla. Hlavním předmětem zkoumání je optimalizace teplosměnných ploch za účelem zvýšení účinnosti výměníku tepla. Tyto cíle byly dosaženy experimentálně a numericky pomocí modelování v ANSYS. Na základě dosažených výsledků byla rozpracována technologie křížového navíjení polymerních výměníků z dutých vláken. Experimentální zařízení původně určené pro navíjení tlakových nádrží bylo modifikované pro automatizovanou výrobu polymerních výměníků z dutých vláken, ježto může být použita při jejich masové výrobě. Tato práce se také zabývala výměníky tepla pro klimatizační systémy. Byly zkoumány možnosti využití polymerních výměníků z dutých vláken v těchto systémech. Mimo jiné byla provedena studie vlivu cyklického tepelného zatížení standardního kovového žebrovaného tepelného výměníku.
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Advanced Inverse Heat Conduction Methods
Komínek, Jan ; Čarnogurská, Mária (referee) ; Hajduk,, Daniel (referee) ; Raudenský, Miroslav (advisor)
Numerical simulations of thermal processes are based on known geometry, material properties, initial and boundaries conditions. The massive use of these simulations in the metallurgical industry (for example for simulation of heat treatment of steel) is limited by the knowledge of precise boundary conditions, which are not easy to determine in compare to other input parameters. Empirical formulas are not sufficiently accurate for most non-trivial processes. Therefore, it is necessary to obtain the boundary conditions by experimental way. Boundary conditions can not be measured directly. The boundary conditions are determined by solving inverse heat conduction problem based on the measured temperature records. This doctoral thesis focuses on two types of the inverse heat conduction problems, which are poorly solved by existing methods. The first type are tasks that contains sharp increase/decrease in the values of the boundary conditions. Two new approaches are proposed and compared in this thesis for this type of tasks. The second type are tasks with non-stationary and non-homogeneous cooling. Three new methods were developed for this case. They are applied for the case of water cooling of vertical aluminum sample. The base characteristics of the current task is inhomogeneous cooling. One part of the surface is cooled intensively by flowing water in contrast to the other part of surface which is cooled only with low intensity since it is protected from direct contact with water by the vapor layer (Leidenfrost effect). The positions of these two part of surface are not stationary (they change during the experiment). The newly developed methods are compared to each other.
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