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SMV-2023-42: Materials for thermal management
Králík, Tomáš
This contract research dealt with so-called solar white coatings with a very different ability to absorb visible radiation and emit thermal radiation. We have studied special coatings designed for the space environment with high emissivity in the field of thermal radiation and at the same time low absorption of radiation originating from the sun or reflected from cosmic bodies. This type of coating is intended for passive thermoregulation of parts of apparatus moving in the space environment. The aim was to determine the so-called total hemispheric emissivity of each of the samples at the required temperatures. For these coatings, the client's goal was also to evaluate the effect of the morphology of the sample on the resulting emission of thermal radiation. Namely, we tested the flat and pyramidal structured surface of the base material. This unique research required a special modification of the supplied samples, modification of the dedicated method for measuring emissivity and absorptivity at cryogenic temperatures, as well as a new procedure for calibration and evaluation of the received data. We used a previously developed shielding ring around the perimeter of the samples to cover the perimeter of the structured samples, which prevented part of the measured thermal radiation from escaping. The results of this research will be used in the design of the CO2M space mission for monitoring CO2 emissions.
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SMV-2023-41: Absorptive coatings for quantum computers
Králík, Tomáš
This contract research focused on the thermal analysis of absorptive layers created by anodic oxidation on aluminium alloy, which are optimized for use at extremely low temperatures. These specific layers were designed for the low-temperature parts of quantum computers, where they play a key role in eliminating the reflection of thermal radiation from the hotter areas of the computer cryostat to the ultra-low temperature areas. Other key requirements for these absorptive layers are high thermal conductivity, necessary for efficient heat transfer within a quantum computer, good mechanical stability and extremely low outgassing to ensure long-term functional behaviour of the layers in challenging low-temperature conditions. The goal of this research was not only to verify the total hemispheric emissivity of three specific types of coatings in the temperature range from 10 K to 300 K. In this case, emissivity is a suitable indicator of the thermal absorptive behaviour of the layer. A study of the emissivity of these layers in the entire spectrum of temperature conditions relevant for quantum computers was carried out. This extensive analysis was intended to provide an insight into the suitability of these absorptive layers for applications in the field of low-temperature technologies, with an emphasis on the requirements of quantum computers.
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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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Cryogenic Technique
Zrůst, Michael ; Milčák, Pavel (referee) ; Kracík, Petr (advisor)
Bachelor thesis deals with technology of cryogenic temperatures, liquefying gases in this temperature interval, effects of these temperatures on materials and insulations. In the introduction, brief history of development of this field. Next part is about gases which get liquefied in cryogenic temperatures and their applications. The largest chapter is chapter about liquefying in which principle of coolers, heat exchangers and liquefiers is described. Next, means of cooling by expansion, cooling cycles used to reach desired temperatures and ways of separating gas mixtures, are specified. In the last chapter insulation used to maintain cryogenic temperatures inside space is discussed.
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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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