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SMV-2015-18: Radiative heat losses in the temperature range from 30 K to 335 K of metallic coatings with various surface treatments including simulation of cleaning on the structural materials for satellites
Králík, Tomáš
Research and development in the field of heat transfer by thermal radiation. The object of the research was verification of heat loses by the thermal radiation from surfaces of materials used for construction of satellites. The samples of the material were coated with metallic film with substantially lower emission of the thermal radiation than of the structural material. This coating was created with variation of the parameters and a cleaning process was simulated on some samples. The emission of the of the thermal radiation was measured with temperature of the sample in the range from 30 to 335 K. The measurement procedure was adapted for some samples because of the lower limit 200 K due to possible delamination of the coating. The study has verified stability of the requested thermal radiative properties of the protective metallic layer with respect to the variation of its production and subsequent cleaning process.
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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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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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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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Emisivita a absorptivita tepelného záření povrchů konstrukčních kovů za velmi nízkých teplot
Musilová, Věra ; Hanzelka, Pavel ; Králík, Tomáš ; Srnka, Aleš
Comparison of thermal radiation properties of surfaces of several metals commonly used in cryogenics is presented. We have measured heat absorbed by a surface of Cu, Al and stainless steel kept at a temperature of about 5 K - 10 K. The source of heat was a parallel black surface placed in a small distance from a tested sample. As a result of our measurement, the dependences of absorptivity on the temperature of the heat radiation source are plotted between 30 K and 140 K. The influence of different types of metal treatment, e.g. chemical and mechanical surface finish and annealing, on radiation heat transfer is presented
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