|
| |
|
|
SMV-2021-40: Thermal emission of CFRP material in vaccum
Králík, Tomáš
This contractual research was focused on the evaluation of the thermal emissivity of material for the structural beam of the space telescope ARIEL. The material is a carbon fibre composite. The knowledge of the thermal emissivity of this material is important for modelling the temperature of the telescope. Its temperature should be passively kept at 55 K only by thermal radiation. The goal of the project was to evaluate the total hemispherical emissivity of the composite in the temperature range from 20 to 300 K. The data was used to decide if the structural beams should be coated with an additional highly emissive layer or not.
|
|
|
SMV-2021-41: Emissivity of the materials for space missions
Králík, Tomáš
This contractual research was focused on evaluation of the thermal emissivity of materials used for space probes to ensure optimal passive thermal control of the device. The ordering party has chosen several types of materials in a form of foils or coated sheets. The materials were shaped to fit in the measurement apparatus. Goal of the project was to evaluate the total hemispherical emissivity in temperature range from 20 to 300 K. The results will help the ordering party to model the temperature distribution cooled in space only by the thermal radiation.
|
|
|
Stainless steels for cryogenic applications processed by 3D printing
Grygar, Filip ; Hutař, Pavel (referee) ; Koutný, Daniel (advisor)
This thesis deals with properties of austenitic stainless steel 304L processed by SLM technology and tested at room and cryogenics temperatures. Result is description of mechanical properties and microstructure. First step was to develop processing parameters to achieve porosity of prints fell below 0,01 %. Following tensile test showed higher yield and ultimate tensile strength than conventionally fabricated parts, even at temperature -80 °C, but at cost of reduced ductility. Due to deformation and low temperature austenite transformed into martensite. This transformation also occurred in Charpy toughness test, that resulted in ductile to brittle behaviour.
|
|
|
SMV-2020-53: Thermal radiation of gold plated surfaces for low temperature applications
Králík, Tomáš
The goal of this experimental study was evaluation of the thermal radiation rate by a surface of an alloy coated with a thin layer of gold. The alloy without gold coating would have of about five time higher rate of the emission or absorption of the thermal radiation. Higher thermal emission makes the thermal control of the parts of space or cryogenics apparatuses more difficult. The contractor has coated three samples of the alloy with gold by various processes. Two other coated samples were cleaned by an industrial cleaning process.\nThe emission of the thermal radiation from the surface of the samples was experimentally evaluated in the range of the sample temperatures from 20 K to 320 K compared to the black body at the same temperature. The results of the study enable to routinely produce parts for satellites or cryogenics with guaranteed thermal emissivity.\n
|
|
|
SMV-2020-25: Emission of electromagnetic radiation by thin gold layers at cryogenic temperatures
Frolec, Jiří
The aim of the contract research was analysis of the ability of gold layers deposited on aluminium substrate to emit electromagnetic waves (thermal radiation) at cryogenic temperatures. Four different samples were designed and fabricated in cooperation with the ordering party. Very low signal of the samples required using of our dedicated instrument together with development of an individual calibration processes for each experiment. The instrument measured emission of thermal radiation at all wavelengths and between temperatures 20 and 320 K, reached using a liquid helium bath. The vacuum was kept by cryopumping so the parasitic heat transfer by the residual gas was negligible. One of the samples reached emissivity values typical for an alloyed gold layer. However, values reached by other three samples were significantly lower, even below the level of our sputtered high purity gold coating. The results allow the ordering party to choose optimal type of surface deposition for their intended application.
|
|
|
Cryogenic Technique
Zrůst, Michael ; Milčák, Pavel (referee) ; Kracík, Petr (advisor)
Bachelor thesis deals with technology of cryogenic temperatures, liquefying gases in this temperature interval, effects of these temperatures on materials and insulations. In the introduction, brief history of development of this field. Next part is about gases which get liquefied in cryogenic temperatures and their applications. The largest chapter is chapter about liquefying in which principle of coolers, heat exchangers and liquefiers is described. Next, means of cooling by expansion, cooling cycles used to reach desired temperatures and ways of separating gas mixtures, are specified. In the last chapter insulation used to maintain cryogenic temperatures inside space is discussed.
|
|
|
SMV-2019-10: Characterisation of Cu alloys at low temperatures
Králík, Tomáš
The goal of the project was to measure the electrical conductivity of eight samples made of pure or alloyed copper at the temperatures 4.2 K, 77 K and 300 K for the as received, annealed and hardened state. The electrical conductivity is correlated with the thermal conductivity and the ratio between electrical conductivity at 300 K and 4.2 K (RRR value) gives the purity of the metal including mechanical defects in the material. Pure copper is excellent conductor of heat and electric current but it does not have required strength properties compared to the alloyed coppers. The measured temperature dependence of the electrical conductivity enables to compare the copper materials and to choose one with optimal properties for the current leads of the fusion reactor. \nThe samples with a cross section 0.15-0.3 mm^2 and length 33-70 mm were cut by slow milling. One of the samples of each material was annealed at 980°C for 1.5 hour and the second was hardened at 480°C for 5 hours. All samples (24 pcs) were soldered with Indium solder on a special holder with contacts for the four wire electric resistance measurement. The electrical resistance was measured by a AC resistance bridge Lake Shore 372.\n
|
|
|
SMV-2019-09: New materials for cryogenics
Králík, Tomáš
The aim of the study was evaluation of the emission of thermal radiation emitted from a set of five commercially available foils which thermal radiative properties unknown till now. These materials are used for insulations of low temperature devices for medicine, industry or space exploration. The emissivity of the materials was measured at conditions truly simulating its operational environment. The measurement was done in a dedicated apparatus cooled with liquid helium. The emissivity of the sample was measured in vacuum at temperatures in the range from 20 K to 300 K.
|
|
|
SMV-2019-76: Maintenance and commissioning of liquid nitrogen Dewar vessel
Králík, Tomáš
The contractor needs a handy storage of liquid nitrogen for some analytical apparatuses in his laboratory. The contractor decided to utilize an older LN2 Dewar vessel with unknown state of its insulation and evaporation rate. A professional commissioning of a Dewar vessel need special know how and specialised equipment. It was done cleaning of the pumping valve of the vessel from old and hardened sealing grease, change of the O-ring sealing, visual check of the insulation inside the vessel, application of new silicone grease on the pumping valve plug, pumping out of the vacuum space and its outgassing, leak test with a helium leak detector, closing of the pumping valve and its filling with silicon grease, cool down and filling with the liquid nitrogen, long term measurement of the evaporation rate. The measured evaporation rate is 0.3 litres per day and the time of the cold state of the Dewar vessel is nearly hundred days.
|
guest ::
