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Národní úložiště šedé literatury Nalezeno 3 záznamů.  Hledání trvalo 0.00 vteřin. 
Fuzzy pressure controller for helium bath cryostats
 Hanzelka, Pavel ; Jura, P.
Pressure stability of about 10 Pa/h is necessary for precise measurementsof the helium evaporation rate of the low loss cryostats. A pressure controller fulfilling this requirement was designed and tested. It consists ofan absolute pressure sensor, an electronic fuzzy controller and a proportional electromagnetic valve. Computer simulation of the system behaviour was used for the controller tuning. The minimization of the final deviationwas preferred to the reaction speed. The operational properties of the controller were verified at the tests of a helium dewar. The controller was utilised at the development of a small helium cryopump.
Úplný záznam
A new construction of rotor of helium expansion turbine
 Dupák, Jan ; Hanzelka, Pavel ; Michalička, Petr ; Tuček, L. ; Ustohal, V.
The aim of our work was to develop a rotor of the expansion turbine designed for a helium liquefier that would enable operation in different modes and achieving of the desired effectiveness at same time. For meeting theserequirements the rotor should enable precise operation of the turbine in the range of 140 000 to 350 000 rqm at minimum heat flow to the low-temperature part of the turbine. Considering the low thermal conductivity and a high strength, the low-temperature part was made of VT3-1 titanium alloy. This contribution is focused mainly on problems of creation of mechanically strong and thermally resistant joint of this part of the rotor with the part working at room temperature.
Úplný záznam
Monte Carlo simulation of molecular flow and radiative heat transfer in He bath cryopump
 Musilová, Věra ; Hanzelka, Pavel ; Srnka, Aleš
A very important parameter of small bath helium cryopump is minimal heat input to its cold parts. Therefore, we simulated both the molecular flow and the thermal radiation heat transfer in the real pump geometry. Monte Carlo particle tracing enables us to compare performances of the pump for different structurses of baffles.
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