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Experimental investigation of the pumps for cryogenic proppellants of the rocket fuel systems
Šuráň, David ; Rudolf, Pavel (referee) ; Kozák, Jiří (advisor)
This bachelor’s thesis deals with the pumping of cryogenic substances. The main objective is a research of experimental investigation of rocket turbopumps. Specific experiments, their purposes, processes and final results including the detailed description of the test rigs are listed. Originally, the work was aimed to pumping of the liquid oxygen (LOX), but it turned out that liquid oxygen simulants are used extensively during the experimental testing. The essential conditions for comparing those substances are stated. Major references were obtained from the experimental investigation technical reports and scientific articles. The rest of the work describes basics of hydrodynamics, pumps and their parameters, cavitation, inducers, rocket combustion cycles and liquid propellants. Finally, author designed a test rig for cryogenic substances pumping.
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Stirling engine
Mader, Dan ; Jedelský, Jan (referee) ; Hejčík, Jiří (advisor)
Presented bachelor thesis deals with study of constructional variations of Stirling engine that work in reverse as heat pump for cooling. First chapter contains history and functional principle of Stirling engine. Second chapter describes Stirling cycle for various devices. The following chapters consist of constructional variations which are divided into three application categories: commercial, military technical, space. In last chapter are these variations compared together and possible future of these devices is being predicted. Result of this thesis is theoretical analysis of Stirling cryocoolers that are based on Stirling engine.
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Stainless steels for cryogenic applications processed by 3D printing
Grygar, Filip ; Hutař, Pavel (referee) ; Koutný, Daniel (advisor)
This thesis deals with properties of austenitic stainless steel 304L processed by SLM technology and tested at room and cryogenics temperatures. Result is description of mechanical properties and microstructure. First step was to develop processing parameters to achieve porosity of prints fell below 0,01 %. Following tensile test showed higher yield and ultimate tensile strength than conventionally fabricated parts, even at temperature -80 °C, but at cost of reduced ductility. Due to deformation and low temperature austenite transformed into martensite. This transformation also occurred in Charpy toughness test, that resulted in ductile to brittle behaviour.
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Spectral analyzing and characterization of magnetic atoms and investigating superconducting films in low temperature STM
Cahlík, Aleš ; Jelínek,, Pavel (referee) ; Šikola, Tomáš (advisor)
This work is divided in two thematic parts. The first part shows a refurbishment of a Omicron low temperature STM set-up and its utilization for preparation of superconducting-magnetic interfaces. First, a cleaning procedure of suitable metallic substrates, specifically W(110) and Ir(111), is shown. It is followed by results of iron monolayer deposition on Ir(111) (Fe-Ir(111) interface). The last section deals with study of vanadium growth on pure Ir(111) substrate as well as on mentioned Fe-Ir(111) interface. The second thematic part deals with magnetism of cobalt atoms on a monolayer metal dichalcogenide WS2. It focuses primarily on studying their magnetic moment and magnetic anisotropy using X-ray magnetic circular dichroism (XMCD).
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The efficiency of heat exchangers in the cryogenic processes
Horvát, Petr ; Krištof, Ondřej (referee) ; Svěrák, Tomáš (advisor)
Heat exchangers and their use in cooling processes are the major topic of this thesis. The theoretical part of the thesis deals with the mechanisms of heat transfer, outlining their problems at low temperature. Furthermore, the thesis describes the types of heat exchangers used in practice, then a relatively large part dealing with the problem of calculations connected with tube heat exchangers is included. Relations for both normal and cryogenic conditions are given. In the experimental part, the heat transfer on the semi-operating glass tube heat exchanger is examined by cooling the room air with 55% ethylene glycol in order to compare the heat-transfer coefficients determined from the heat balances and from the dimensionless criteria based on the relations mentioned in the theoretical part of the thesis. For a pair of coolant flows and four airflows, input and output flow temperatures, pressure and relative air humidity at the inlet were measured. At higher airflows, more than double efficiency of heat exchange was observed, at the lowest airflow the exchanged heat was up to half against the theoretical model. The reason for these deviations is probably the condensation of air humidity in the heat exchanger and the design of the heat exchanger. The flow of coolant had practically no influence on the amount of heat exchanged. As found, for the studied heat exchanger it is non-effective to operate in low airflow modes and it is unnecessary to operate at higher flow rates of the cooling medium.
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Materials and their application in low temperature parts of STM microscope
Voňka, Jakub ; Vlček, Ivan (referee) ; Urban,, Pavel (advisor)
Průtokvý kryostat s kapalným héliem (LHe) je vyvíjen skupinou Kryogeniky a Supravodivosti na Ústavu Přístrojové Techniky pro stávající rastrovací tunelovací mikroskop (STM) pracující za pokojové teploty na Ústavu Fyzikálního Inženýrství. Tato bakalářská práce se zabýva výběrem materiálů a určením jejich vlastností pro potenciální využití v některých částech nízkoteplotního STM mikroskopu (LT-STM), se zaměřením zejména na tepelnou vodivost v teplotním rozsahu od 4 K do 300 K. Je zde probírána problematika měděných svazků pro tepelné spojení vzorku s tepelným výměníkem. Slitina CuCrZr byla podrobně zkoumána jako vhodný materiál pro držák vzorku. Byly určeny tepelné toky málo vodivými podpěrami založenými na styku sférických ploch pro použití jako izolace mezi studeným držákem vzorku a STM stolkem.
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Design and verification of low temperature part of UHV – STM microscope
Voňka, Jakub ; Rotter, Miloš (referee) ; Urban, Pavel (advisor)
The diploma thesis addresses the design and experimental verification of cooling system and low temperature part of UHV - STM working in temperature range of 20K - 300K. Due to the demand of variable temperature, the flow cooling system with cryogenic (~5 K) helium (He) is used. Two variants of the low temperature part of the microscope are studied. First the version with cooling only the sample holder, and second with cooling of the whole STM. Designed cooling system consists of He flow cryostat allowing to connect it to the Dewar vessel with liquid helium (LHe) using a low-loss transfer line. The cryostat consists of He inlet and outlet, heat exchangers and copper strains (i.e. braids) for the thermal connection of the sample holder/STM and radiation shield around the STM with the heat exchangers. The thesis describes the design of the flow cryostat and its initial tests in the designed vacuum chamber. Heat flow through a spot contact is also discussed to estimate thermal conductance of insulation supports based on thermal resistance of spherical contacts. The thesis was elaborated in collaboration with the Institute of Scientific Instruments of the ASCR, v.v.i.
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Low temperature scanning tunneling microscopy
Sojka, Antonín ; Havlíček,, Marek (referee) ; Pavera, Michal (advisor)
The diploma thesis is divided into two main parts. The first part describes the production of chrome and cobalt tips for SP-STM with subsequent testing of chrome tips on the Fe-Ir system (111). Furthermore, the first results from the growth studies of niobium on iridium(111) are presented. In the second part is described in detail the experimental LT-STM microscope of the Faculty of Physical Engineering. The chapter deals with the development of the microscope and its testing on a HOPG sample under atmospheric and vacuum conditions. The chapter describes the biggest problems which were solved when the microscope was puting into operation state. The second part also introduces the design of a new vacuum transport system, which consists of a tip and sample transport pallet. At the end of the second part is described the testing of cooling systems for LT-STM and the design of their modifications.
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Design of a nitrogen Dewar vessel for electron microscopes
Brauner, Tomáš ; Voňka,, Jakub (referee) ; Urban, Pavel (advisor)
Observation of biological samples in electron microscopes in a state closest to the native state requires reaching cryogenic temperatures, most often with the use of liquid nitrogen (LN2). For this purpose a Dewar vessel with cooled copper thumb for cooling the sample holder and anticontamination shield inside the vacuum chamber of the scanning electron microscope (SEM) and focused ion beam (FIB) source was designed. Characteristics of the designed LN2 Dewar vessel were validated by measuring executed on the real functional sample. The reached temperature at the tip of the thumb under estimated heat load 2 W was 90,8 K. Corresponding refilling interval of LN2 is about 11 h. Experimentally measured data correlate with theoretically calculated characteristics. The designed Dewar vessel with a cooled thumb fulfills the required properties specified in the thesis assignment with a margin.
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Stainless steels for cryogenic applications processed by 3D printing
Grygar, Filip ; Hutař, Pavel (referee) ; Koutný, Daniel (advisor)
This thesis deals with properties of austenitic stainless steel 304L processed by SLM technology and tested at room and cryogenics temperatures. Result is description of mechanical properties and microstructure. First step was to develop processing parameters to achieve porosity of prints fell below 0,01 %. Following tensile test showed higher yield and ultimate tensile strength than conventionally fabricated parts, even at temperature -80 °C, but at cost of reduced ductility. Due to deformation and low temperature austenite transformed into martensite. This transformation also occurred in Charpy toughness test, that resulted in ductile to brittle behaviour.
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