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Přenos tepla napříč superizolacemi z pokojových do nízkých teplot
Hirschl, Ch. ; Králík, Tomáš ; Laa, Ch. ; Musilová, Věra ; Schmid, T. ; Stipsitz, J.
For more than 30 years thermal measurement results and analytical formulas are available to calculate the heat transfer through Super Insulation (SI). According to the temperature dependence of the emissivity for aluminium, the most commonly used material for the reflecting surfaces, derivations based on the Stefan-Boltzmann-Law for radiative heat transfer have been established. Together with conductive terms this leads to formulas for the calculation of heat transfer through SI. Using new measurement results of temperature-dependent emissivity and conductivity we have performed heat flux calculations applying common software tools. The heat transfer through the SI and the temperature distribution inside the SI calculated with this new approach has been compared with the established formulas and measurement results.
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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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Zařízení pro měření tepelné emisivity při nízkých teplotách
Králík, Tomáš ; Hanzelka, Pavel ; Musilová, Věra ; Srnka, Aleš
In the described device, the thermal emissivity or absorptivity of the sample is measured by substitution of the radiative heat flow between two parallel surfaces by thermal output of a heater. Fast measurements of the mutual emissivity for the range of the temperature of the radiating surface 25 K - 150 K are possible. The absorbing surface has a temperature between 5 K and 10 K when LHe is used as cryoliquid. The desired measurement sensitivity is 1 mK for temperature and 0.1 mikroW for heat power, respectively. The diameter of the whole device is 50 mm and so it is possible to use a commercial Dewar can for the cooling. The form of the sample is a circular plate 40 mm in diameter and 1 mm in thickness with one tested side. The emissivity and its temperature dependence for various surface treatments can be checked immediately before application in a cryogenic system
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