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SMV-2019-31: Design and production of sample vessels for liquid nitrogen with volume 1 litre
Srnka, Aleš
The aim of the project is design of small transport vessels for liquid nitrogen with volume according customer demands and production of tests samples according customer. The origin of this know-how is in the institute, it is 47 years old. It is necessary to check actual quality of raw material, to define its volume for given vessel type and check the time of production, that is dependent on the volume and vessel shape and also on the raw material characteristic. After checking all of important parameters the form with defined volume for is prepared and test sample are produced. Samples are after detailed testing sent to the customer. Research was conducted according order dated 19.4.2019 (No. 19227).\n\n
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SMV-2019-32: Design and production of sample vessels for liquid nitrogen with volume 1.3 litre
Srnka, Aleš
The aim of the project is design of small transport vessels for liquid nitrogen with volume according customer demands and production of tests samples according customer. The origin of this know-how is in the institute, it is 47 years old. It is necessary to check actual quality of raw material, to define its volume for given vessel type and check the time of production, that is dependent on the volume and vessel shape and also on the raw material characteristic. After checking all of important parameters the form with defined volume for is prepared and test sample are produced. Samples are after detailed testing sent to the customer. Research was conducted according order dated 13.11.2019 (No. 0830447-3405-70109).\n\n
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SMV-2019-30: Design and production of sample vessels for liquid nitrogen with volumes 0.35 l, 0.75 l and 1.3 l
Srnka, Aleš
The aim of the project is design of small transport vessels for liquid nitrogen with volume according customer demands and production of tests samples according customer. The origin of this know-how is in the institute, it is 47 years old. It is necessary to check actual quality of raw material, to define its volume for given vessel type and check the time of production, that is dependent on the volume and vessel shape and also on the raw material characteristic. After checking all of important parameters the form with defined volume for is prepared and test sample are produced. Samples are after detailed testing sent to the customer. Research was conducted according two orders, 1st dated 19.2.2019 (No. 021919-02) and the 2nd dated 18.6.2019 (No. 061719-03 Rev 1).\n\n
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SMV-2019-28: Research of thermal conductivity of samples from different materials in temperature range 10 – 80 K
Srnka, Aleš
The aim of the project was R&D of measurement apparatus for assess of thermal conductivity of materials, especially metalic, which are used in cryogenic rotary machines. After R&D steps and basic tests of apparatus, there was in the apparatus tested thermal conductivity of sample, that was delivered by contractor. After finished experiments, the measurement protocol was passed on to contractor. The research is conducted according Contract between PBS a.s. Velká Bíteš and ÚPT AV ČR Brno, v.v.i., signed on the 17.9.2018 and according order No. 84302181 from 9.10.2018.\n
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SMV-2019-29: Professional servis of Dewar vessels for LHe
Srnka, Aleš
The aim of the project is optimalization of the operation of Dewar vessels for liquid helium with\naccent to the safe operation and its economical benefit. Vessels are periodically tested for vacuum tightness and relevant boil of rate is measured. Simultaneously are tested security valves and cooling processes of vessels are optimized. We use long time know-how in the field of cryogenics and also our specialized cryogenics equipments and apparatuses. The research is conducted according Contract between MU - CEITEC and ÚPT AV ČR Brno, v.v.i., signed on the 17.1.2019. \n
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Effect of thermal radiation on low temperature measurement for various types of temperature sensor installations
Urban, Pavel ; Hanzelka, Pavel ; Králík, Tomáš ; Vlček, Ivan ; Srnka, Aleš
We investigated an effect of thermal radiation (300 K) on precision of low temperature measurement of a sample holder (or sample) in an UHV SEM/SPM microscope working at range down to 20 K for various ways of temperature sensor mounting. We designed a special copper casing for installation of Lake Shore\ntemperature sensors (CernoxTM and Si diodes) encapsulated in SD packages. The sensor body is attached direct to the casing using indium solder. The current leads pertaining to the sensor are thermally anchored but electrically insulated from the casing. Quality of sensors installation in the casing was tested for various ways of mounting on a cooled plate. Insufficient thermal anchoring of electrical wires and thermal shielding were imitated. Comparative measurement was also performed with sensors in SD package mounted without\ncasing. The experiments proved that our special design of temperature sensors casing is adequate for intended application of temperature measurement of sample holder in UHV SEM/SPM microscope. In contrary, measurement precision of unprotected sensors was absolutely unsuitable.
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Role of the superconductivity in radiative heat transfer
Králík, Tomáš ; Musilová, Věra ; Srnka, Aleš ; Fořt, Tomáš ; Frolec, Jiří
The absorption and emission of thermal radiation by metals is related to their electrical properties that are influenced by impurities, defects and temperature. We show by some examples of measurements on common metals how different can be the thermal radiative properties. When the heat is transferred across a microscopic vacuum gap in the near field regime, it is possible to achieve a step-like change of the heat\ntransfer based on a superconducting transition. An interesting feature of this effect is the nonlinear thermal conductivity effecting a change of the sign of the differential thermal conductivity across the vacuum gap.
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SMV-2014-14: Baffle plates for the 75 mm neck of the helium Dewar CH-500
Srnka, Aleš
Research and development in the field of thermal shielding of cryogenic vessels. It included selection of material with suitable emisivity and absorptivity of thermal radiation, analysis of cryogenic vessel from the point of parasitic thermal fluxes and calculation of baffles quantity and position in the vessel neck. Experimental tests proved rightness of calculation and showed that only by use of properly designed baffles it is possible to reach minimal helium evaporation rate.
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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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