Atomization mechanisms of liquid fuels

Bakalářská práce se zabývá problematikou rozprašování kapalných paliv. Hlavním cílem práce je seznámit se se základními typy rozprašovačů a mechanismy, které jsou zodpovědné za rozpad kapaliny. V první části práce jsou popsány základní typy rozprašovačů, neboli atomizérů, a základní faktory ovlivňující rozprašování. Další část je věnována základním mechanismům rozpadu proudu kapaliny a kapek. Závěrečná část se zabývá statistickými metodami pro popis sprejů a popisem vyvinutého programu pro vyhodnocení experimentálních dat.The bachelor thesis deals with the atomization of liquid fuels and their atomizers and mechanisms which are concerned in atomization. The main purpose of this thesis is to describe the problems that are connected with the atomization. The author gives information about the primary and secondary decomposition of liquid. One part of the thesis is the software which focuses on the statistic evaluation and comparison of information which are performed by available experiments and numeric calculations.

Design of heat exchanger

Diplomová práce je zaměřena na tepelně-hydraulický a pevnostní návrh tepelného výměníku s U-trubkovým svazkem uvnitř pláště. Úvodní část práce seznamuje s problematikou návrhu tepelného výměníku. Další část popisuje tepelně-hydraulický návrh vytvořený v softwaru Maple 16.0 pomocí Kernovy metody a metody Bell-Delaware. Kontrola tepelně-hydraulického návrhu je provedena v softwaru HTRI. Pro kontrolu kritických míst proudícího média v mezitrubkovém prostoru je vytvořen CFD model v softwaru ANSYS Fluent 14.0. Pevnostní návrh je vytvořen v softwaru Sant’Ambrogio dle normy ČSN EN 13 445. V poslední části je zkontrolováno hrdlo návrhem dle analýzy tedy pomocí MKP dle normy ČSN EN 13 445.The master thesis deals with thermal hydraulic design and strength design of a heat exchanger with “U” tube bundle inside of a shell. The first chapter introduces general design issues of the heat exchangers. The following chapter describes thermal hydraulic design created in software Maple 16.0 by using Kern’s method and the method of Bell-Delaware. HTRI software was used for the control of thermal hydraulic design correctness. To check critical locations of fluid flow in space between the tubes, the CFD model was created at ANSYS Fluent 14.0 software. Accuracy of strength design was verifying by Sant’ Ambrogio software in accordance with ČSN EN 13 445 standards. The last chapter concerns with FEM analysis. According to standards ČSN EN 13 445 the design by analysis namely method based on stress categories were used for the strength analysis of nozzle.

Evaluation of the technical condition of medium-sized boilers

The recent trend in the steam and electricity production has been both to increase the efficiency of the facility and to keep tightening legislation concerning emission limits. The lifetime of energy equipment is greatly influenced by the operating temperature, pressure and operating characteristics. The new conditions lead the operator to more often changes of these parameters, which has negative influence to the facility in terms of service life. Precise knowledge of the facility being operated and the ability to predict the residual life of its key parts in time is therefore necessary. A new methodology for determining the residual life and evaluating problematic situations of medium size boilers was developed at Brno University of Technology. Its approaches and advantages will be presented in this paper. The methodology provides the user with approaches for the lifetime evaluation of an equipment as a whole, based on detailed knowledge of the equipment being investigated and the ongoing damage. Additionally, if the equipment is continuously evaluated, it is possible to extend the inspection interval or to achieve a significantly higher lifetime of the entire equipment, thereby reducing the economic cost. If defined criteria are met, the methodology also allows inclusion of FEM and CFD simulations for achieving higher relevance of the results

Thermal load non-uniformity estimation for superheater tube bundle damage evaluation

Industrial boiler damage is a common phenomenon encountered in boiler operation normally which usually lasts several decades. Since boiler shutdown may be required because of localized failures, it is crucial to predict the most vulnerable parts. If damage occurs, it is necessary to perform root cause analysis and devise corrective measures (repairs, design modification, etc.). Boiler tube bundles, such as those in superheaters, preheaters and reheaters, are the most exposed and often the most damaged boiler parts. Both short-term and long-term overheating are common causes of tube failures. In these cases, the design temperatures are exceeded, which often results in decrease in remaining creep life. Advanced models for damage evaluation require temperature history, which is available only in rare cases when it has been measured for the whole service life. However, in most cases it is necessary to estimate the temperature history from available operation history data (inlet and outlet pressures and temperatures etc.). The task may be very challenging because of the combination of complex flow behavior in the flue gas domain and heat transfer phenomena. This paper focuses on estimating thermal load on superheater tubes via Computational Fluid Dynamics (CFD) simulation of flue gas flow including heat transfer within the domain consisting of a furnace and a part of the first stage of the boiler

Flow Induced Vibration Fatigue Analysis of Tube Bundle

Hlavním cílem dizertační práce je kontrola trubkového svazku na cyklickou únavu způsobenou prouděním pracovního média v mezitrubkovém prostoru. Únava způsobená prouděním je způsobena vibracemi vyvolanými prouděním. Zkoumané vibrace jsou vyvolány vzájemnou interakcí dvou fází (pevné a tekuté). Předkládaná práce je zaměřena především na interakci trubkových svazků s tekutinou. Současná úroveň poznání v této oblasti umožňuje predikovat především únosnost v oblasti statického, resp. kvazi-statického zatížení. Tyto predikce jsou založeny na metodách srovnávající klíčové vibrační veličiny, jako jsou frekvence, amplitudy, případně rychlosti (viz. TEMA [1]). Tímto způsobem je možno rychle a relativně přesně určit výskyt vibrací, není však možné kvantitativně hodnotit vliv těchto vibrací na poškození trubkového svazku a predikovat tak jeho životnost, k čemuž by bylo zapotřebí určit např. teplotní pole a rozložení sil od tekutiny na tomto svazku. Současné metody numerických analýz velmi dobře umožňují řešit tuto problematiku velmi přesně avšak na úkor výpočtového času, výpočetních prostředků a licencí. Přínosem této práce je využití uživatelem definovaných funkcí (UDF) jakožto metody, která umožňuje napodobit interakci tekutiny a struktury v softwaru ANSYS Fluent. Tato práce klade velkou váhu na využití metod současného stavu poznání pro verifikaci a validaci výsledků, pro ověření výše zmíněné metody. Pro verifikaci a validaci výsledků jsou použity například experimentálně naměřené závislosti Reynoldsova a Strouhalova čísla, odporového součinitele nebo např. rozložení tlakového součinitele kolem trubky. Zároveň využívá metodu konečných prvků jakožto nástroje pro napěťově-deformační výpočet klíčové části na trubce, jakou je spoj trubka-trubkovnice. Dalším přínosem této práce je rozšíření grafického návrhu tepelného výměníku dle Poddara a Polleyho [2] o kontrolu na vibrační poškození dle metody popsané v publikaci TEMA [1]. Předkládaná práce upozorňuje na obrovský vliv rychlosti proudících tekutin jak na trubkové, tak mezitrubkové straně pro návrh tepelného výměníku. Jako etalon poškození si autor vybral výměník s označením 104 z publikace Heat Exchanger Tube Vibration Data Bank [3]. U tohoto výměníku bylo prokazatelně zjištěno vibrační poškození vlivem přestřižení trubek o přepážky. V poslední části jsou nastíněny možnosti a limity dalšího pokračování této práce.The aim of the dissertation thesis is the control of the tube bundle on the cyclic fatigue caused by the flow past tube bundle. Fatigue due to flow is caused by flow-induced vibrations. Examined vibrations are caused by the mutual interaction of two phases (solid and liquid). The present work is focused mainly on the interaction of tube bundles with fluid. The current level of knowledge in this field allows to predict mainly static respectively quazi-static loading. These predictions are based on methods of comparing key vibration variables such as frequencies, amplitudes or speeds (see TEMA [1]). In this way, it is possible to determine quickly and relatively precisely the occurrence of a vibrational phenomenon, but it is not possible to quantitatively assess the effect of these vibrations on the damage of to the tube beam and to predict its lifespan, which would require the determination of the temperature field and the distribution of forces from the fluid on the beam. The aim of the work is to evaluate the-state-of-the-art, to perform a numerical simulation of the flow of fluids in the area of shell side under the inlet nozzle. Current methods of numerical analyses very well solve this problem, but at the expense of computing time, devices and expensive licences. The benefit of this work is the use of user-defined function (UDF) as a method for simulating interaction with fluid and structure in ANSYS Fluent software. This work places great emphasis on using the current state of knowledge for verifying and validation. Verifying and validation of results include, for example, experimentally measured Reynolds and Strouhal numbers, the drag coefficients and for example magnitude of pressure coefficient around the tube. At the same time, it uses the finite element method as a tool for the stress-strain calculation of a key part on tube such as a pipe-tube joint. Another benefit of this work is the extension of the graphical design of heat exchanger according to Poddar and Polley by vibration damages control according to the method described in TEMA [1]. In this section, the author points out the enormous influence of flow velocity on both the tube side and the shell side for design of the heat exchanger to ensure faultless operation. As an etalon of damage, the author chose a heat exchanger designated 104 from the Heat Exchanger Tube Vibration Data Bank [3]. With this heat exchanger, vibrational damage has been proven to be due to cutting of the tubes over the baffles. The last part outlines the possibilities and limits of further work.

Evaluation of the technical condition of medium-sized boilers

The recent trend in the steam and electricity production has been both to increase the efficiency of the facility and to keep tightening legislation concerning emission limits. The lifetime of energy equipment is greatly influenced by the operating temperature, pressure and operating characteristics. The new conditions lead the operator to more often changes of these parameters, which has negative influence to the facility in terms of service life. Precise knowledge of the facility being operated and the ability to predict the residual life of its key parts in time is therefore necessary. A new methodology for determining the residual life and evaluating problematic situations of medium size boilers was developed at Brno University of Technology. Its approaches and advantages will be presented in this paper. The methodology provides the user with approaches for the lifetime evaluation of an equipment as a whole, based on detailed knowledge of the equipment being investigated and the ongoing damage. Additionally, if the equipment is continuously evaluated, it is possible to extend the inspection interval or to achieve a significantly higher lifetime of the entire equipment, thereby reducing the economic cost. If defined criteria are met, the methodology also allows inclusion of FEM and CFD simulations for achieving higher relevance of the results

Thermal load non-uniformity estimation for superheater tube bundle damage evaluation

Industrial boiler damage is a common phenomenon encountered in boiler operation which usually lasts several decades. Since boiler shutdown may be required because of localized failures, it is crucial to predict the most vulnerable parts. If damage occurs, it is necessary to perform root cause analysis and devise corrective measures (repairs, design modifications, etc.). Boiler tube bundles, such as those in superheaters, preheaters and reheaters, are the most exposed and often the most damaged boiler parts. Both short-term and long-term overheating are common causes of tube failures. In these cases, the design temperatures are exceeded, which often results in decrease of remaining creep life. Advanced models for damage evaluation require temperature history, which is available only in rare cases when it has been measured and recorded for the whole service life. However, in most cases it is necessary to estimate the temperature history from available operation history data (inlet and outlet pressures and temperatures etc.). The task may be very challenging because of the combination of complex flow behaviour in the flue gas domain and heat transfer phenomena. This paper focuses on estimating thermal load non-uniformity on superheater tubes via Computational Fluid Dynamics (CFD) simulation of flue gas flow including heat transfer within the domain consisting of a furnace and a part of the first stage of the boiler