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SMV-2013-27: Thermal radiation absorptivity for development of multilayer insulation for alternating electromagnetic fields
Králík, Tomáš ; Hanzelka, Pavel
Super insulations composed of many layers of metalized plastic foils are one of the ways of significant heat flow reduction to low temperature parts of the apparatus. The metal layer was modified to reduce heat generation by alternating electromagnetic fields (e.g. in superconducting motors, generators or transformers). The modifications of the metallisation always worsen the thermal radiative properties of the foils and it was needed to evaluate its influence. The absorptivity of thermal radiation was evaluated in the experimental study on two foils coated with metallic film divided in segments and on the foil coated with metallic particles dispersed in a binder.
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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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Factors Influencing Thermal Radiative Properties of Metals
Králík, Tomáš ; Hanzelka, Pavel ; Musilová, Věra ; Srnka, Aleš
Data on thermal absorptivity and emissivity are important for calculations of heat flows in cryogenic devices. Although thermal radiative properties of materials used in cryogenics are measured, published and used for more than sixty years we have noticed that sometimes users of that data don’t well understand the significance of individual factors influencing thermal radiative properties. The sensitivity of the thermal radiative properties of metals to the condition of the surface and the difficulty of measurement, especially at low temperatures is probably the reason of dispersion of the published values. The effect of the material and its purity, finishing (machining, mechanical or chemical polishing) and of the protective coatings or accidental layers (water, oxidation) on the thermal radiative properties is not always obvious. Influence of the material, surface treatment, roughness and layers on the surface is discussed on the basis of our 20 year experience with measurement of the emissivity and absorptivity in the range from 20 K to 300 K.
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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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Marketing of Green Companies
Nováková, Pavla ; Štědroň, Bohumír (advisor) ; Králík, Tomáš (referee)
The goal of this Master's Thesis was to map and asses marketing of Green Companies in the Czech Republic and abroad and based on some basic characteristics to evaluate the economical profitability of this business and its future prospects. The Thesis is about ecological products and customer's possibilities to become informed enough about them and to choose the right one. The Thesis focuses on some companies operating on the energy market. These companies are very often placed on the top of green rankings. Based on my experience environmental activity is evaluated in the department of operating leasing in the ČSOB Leasing a.s. company.
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Černé povrchy pro použití v kryotechnice
Králík, Tomáš ; Hanzelka, Pavel ; Musilová, Věra ; Srnka, Aleš
Surfaces with high absorption or emission of thermal radiation are often needed in cryogenic and space applications. It is more difficult to realize a sufficiently black surface applicable in cryogenic systems than to make highly reflective surfaces. Experimental results on black surfaces like epoxy coatings, paints and thin films concerning the thermal radiative properties (emissivity and absorptivity) in the temperature range from 20 K to 300 K of the source of the thermal radiation are presented.
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