National Repository of Grey Literature 42 records found  beginprevious25 - 34next  jump to record: Search took 0.00 seconds. 
SMV-2015-19: Influence of the compression on the thermal conductivity of the MLI spacers
Králík, Tomáš
The experimental study was aimed on characterisation of the thin insulation materials – spacers used in multilayer insulations (MLI). The MLI is composed of reflective foils interleaved by insulating spacers. The samples were made of various materials (glass fibre, polyester, silk). The measurement was done in unique apparatus developed at ISI Brno in the year 2014. The main goal of the study was to evaluate the influence of the compression by a precisely controlled load on the thermal conductivity in the range of temperatures 10 K and 300 K. The not yet available results of the study enable optimisation of the MLI with requested properties.
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.
SMV-2014-21: Thermal properties of MLI spacers
Králík, Tomáš
The goal of the project is to develop and build an apparatus enabling to measure the heat flow across a sample of the MLI spacer. This is thin woven or nonwoven textile. The requested parameter of the measurement is precisely controlled compression of the sample between contact surfaces with defined temperature in the range of 10 K – 300 K. The compression equals to the load 0.2 g-2 g and it has to be constant despite the thermal dilatations in the apparatus. An electromechanical loading system with load sensor in a feedback control placed in the warm part of the apparatus was developed for this apparatus. The force is mechanically transferred to the cryogenic part of the apparatus.
SMV-2014-06: Measurement of temperature dependence of the emissivity of samples with various types of surface finishing and coatings in the temperature range of 40 K – 300 K
Králík, Tomáš
Research and development in the field of heat transfer by thermal radiation. The object of the research was emission of the thermal radiation from metallic surfaces with various treatments in the temperature range from 40 K to 300 K. The influence of the surface quality and type of the material on the emissivity and absorptivity was evaluated.
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.
SMV-2013-10: Experimental evaluation of thermal radiative properties of device surfaces designed for space operation
Králík, Tomáš ; Frolec, Jiří
A new generation of meteorological satellites will be equipped with a sensor cooled at low temperature. A surface treatment of the cryostat parts has to be optimized with respect to the absorptivity of thermal radiation and demands on the finishing operations of the parts surface.
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.
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.
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].
Radiative Heat Transfer at Low Temperatures over Microscopic Distances in Vacuum
Králík, Tomáš ; Musilová, Věra ; Hanzelka, Pavel ; Horák, Michal ; Srnka, Aleš
We present experimental results on heat transfer between plane parallel surfaces of samples separated with microscopic vacuum gap. Radiative heat flux between metallic samples exceeding 50 times heat flux between black surfaces was observed for gaps of several micrometres at temperatures below 50 K. Comparison with near field theory of radiative heat transfer is presented.

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33 Králik, Tomáš
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