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Design and verification of low temperature parts of UHV SEM/SPM stage
Pola, Tomáš ; Vlček, Ivan (referee) ; Urban, Pavel (advisor)
This thesis focuses on experimental verification and experimental-based improvements of designed low temperature parts of stage of the UHV SEM/SPM microscope, which operates in temperature range from 20 K to 700 K. The main focus is on the functionality verification of thermal insulation pad (InBallPad) as well as on the effect of length and contact quality of braid on minimal achievable temperature. The contact quality of sample holder with sample carrier realized with two springs is investigated together with influence of thermal contact resistances on achievable temperature. The thesis also contains a calculation model used for cooldown times and minimal temperature estimation. In the conclusion of this work several future experiments are suggested which could explain some of the observed, yet unexpected, phenomena.
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Visualization of cryogenic helium flow using of laser-induced-fluorescence
Drahotský, Jakub ; Šiler, Martin (referee) ; Urban, Pavel (advisor)
This work evaluates the laser induced fluorescence method (LIF) for the vizualization of the cryogenic helium flows for experimental study of the Rayleigh–Bénard convection at the Institute of Scientific Instruments (ISI) in Brno in the labs of Cryogenics and Superconductivity group. As the tracer particles, we considered the metastable molecules He2*, that are created by the ionization of helium with themfemtosecond laser pulse and then they are excited by the lasers with appropriate wavelengths for the invocation of the fluorescence. On the basis of the research study, I have evaluated the current laser equipment at the ISI as insufficient for the experiment realization. At the end of this work, there is a list of a laser technique and other devices which are necessary for the adaptation of the LIF method in the experiments at ISI.
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The Study of the Contract Award in Selected Company
Urban, Pavel ; Ing.Miloslav Krejbych (referee) ; Jurová, Marie (advisor)
The main topic of this bachelor thesis is to make a draft of process of contract in the company to maximum satisfaction with a focus on delivery schedules, quality and costs. Specifically in the company Cimbria HMD Ltd. Litomyšl which deals with manufacturing and servicing of after-harvest machinery. The theoretical part deals with information about project management. According to identified deficiencies from analysis of the current status of the contract, I deal with on its improvement.
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Helium Cryostat for Experimental Study of Natural Turbulent Convection
Urban, Pavel ; Jícha, Miroslav (referee) ; Rotter, Miloš (referee) ; Fedor,, Ján (referee) ; Musilová, Věra (advisor)
V disertační práci je popsán heliový kryostat s experimentální válcovou konvekční celou pro studium proudění při přirozené konvekci za velmi vysokých Rayleigho čísel Ra (až do řádu 10^15) a Nusseltových čísel Nu (až do řádu 10^4). Pracovní látkou je studené 4He, které umožňuje díky výhodným fyzikálním vlastnostem dosažení velmi vysokých hodnot čísel Ra. Návrh kryostatu je založen na koncepci lázňových NMR kryostatů s nízkým odparem kryokapalin. Ve středu kryostatu je umístěna konvekční cela o průměru 300 mm a výšce 300 mm. Celu tvoří horní a spodní dno a výměnná střední část. Tyto díly jsou spojeny rozebíratelnými přírubami těsněnými indiovým drátem. Výměnná část umožňuje snadnou modifikaci geometrie cely. Hlavní přednost kryostatu spočívá v minimálním vlivu konstrukce cely a použitých materiálů na studovanou konvekci. Cela kryostatu je navržena pro pracovní tlaky do 250 kPa.
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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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SMV-2015-23: Development of a low temperature system for a spectroscopy
Urban, Pavel ; Hanzelka, Pavel
The system for measurement of temperature of solid and liquid samples for spectroscopic measurement in the range of 77 K - 300 K was designed. For the above mentioned system, the pump vacuum line was designed and analysed for pumping of vacuum spaces of two types of liquid nitrogen cryostats used for spectroscopic measurements. The part of the solution is design of temperature sensor positions and an electrical resistance heater for the sample temperature stabilisation. Furthermore, an electrical resistance heater for heating/outgassing of the vacuum pump line was designed.
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Design of Balanced Scorecard information system
Urban, Pavel ; Mildeová, Stanislava (advisor) ; Tupý, Martin (referee)
This thesis is about Balanced Scorecard methodology and about information systems that support Balanced Scorecard in business. The main goals for the thesis are creating a design of Balanced Scorecard for an existing company and then design a BSC information system for this company. Business strategy management is introduced in the beginning of the theoretical part of this thesis. The description of each perspective of Balanced Scorecard follows. There is also a focus on BSC and strategy modifications over the time and one chapter is devoted to metrics, different types of metrics and relationships between them. Application part introduces the company used in the thesis. Based on the knowledge from the theoretical part the Balanced Scorecard is designed for this specific company and then an information system design is created.
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Design and Testing of Low Temperature Part of an UHV – SPM Microscope
Frolec, Jiří ; Vonka, J. ; Hanzelka, Pavel ; Králík, Tomáš ; Musilová, Věra ; Urban, Pavel
We have developed low temperature part of an ultra high vacuum scanning probe microscope (UHV-SPM) working at variable temperature within the range from 20 K to 700 K. To achieve the required temperature range, a flow cooling system using cryogenic helium (approximately 5 K) as a coolant was designed. The system consists of a flow cryostat and a flexible low-loss transfer line connecting a Dewar vessel with the flow cryostat. We have also tested liquid nitrogen (approximately 77 K) as an alternative low-cost coolant. Using nitrogen, the microscope can operate at temperatures of about 100 K and higher. As the flow of the coolant through the cryostat can cause thermally induced two-phase flow fluctuations resulting in instability in temperatures, preliminary tests were done in order to find ways of avoiding the temperature oscillations and optimising the cooling process.
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Temperature Inversion and Heat Transport Against the Temperature Drop in Two-Phase Convection of Cryogenic Helium
Urban, Pavel ; Schmoranzer, D. ; Hanzelka, Pavel ; Skrbek, L.
In the system of two bodies A and B connected by a two-phase vapour-liquid system consisting only of cryogenic helium, we observed anomalous heat transport from the colder but heated body B to the warmer but cooled body A. We noticed this effect during the process of liquid evaporation inside a cylindrical pressure convection cell used for study of Rayleigh-Bénard convection. This anomalous heat transfer occurs under non-equilibrium conditions, owing to the phase transitions that take place inside the cell while temperature inversion develops between the heated but cooler bottom plate and the cooled but warmer top plate. This process is, by virtue of the system being open with respect to heat transport, in no contradiction to the second law of thermodynamics, and a numerical model was formulated that describes the observations with good agreement.
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Cryogenic He experiment on Natural Turbulent Convection
Králík, Tomáš ; Urban, Pavel ; Musilová, Věra ; Hanzelka, Pavel ; Srnka, Aleš ; Repisky, Andrej
Cryogenic helium gas is a suitable fluid for study of natural turbulent convection at very high Rayleigh numbers. We present experimental method and new result on Reynolds and Péclet numbers characterizing large scale circulation (LSC) of fluid at Rayleigh numbers within the range from 1011 to 1015. Observation of LSC is based on measurement of local temperature fluctuations of convecting helium. For experiments we used a specially designed cylindrical cell of height L = 0.3 m and diameter D = 0.3 m with minimized parasitic effects on studied convection, previously published on CryoPrague 2006 [1].
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