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Návrh a testování kryostatu s experimentální celou pro turbulentní tepelnou konvekci
Urban, Pavel ; Hanzelka, Pavel ; Musilová, Věra ; Srnka, Aleš ; Skrbek, Ladislav
We have designed an experimental cell of He cryostat for the study of the turbulent natural convection at very high Rayleigh numbers (1e6 < Ra < 2e15) with cryogenic 4He gas as a working fluid. The main goal of our study is to resolve the question about the transition to an ultimate Kraichnan regime within a range of available Ra, as similar experiments with cryogenic 4He gas performed in Chicago, Grenoble, Oregon and Trieste gave controversial results. The Grenoble group claimed to observe the Kraichnan regime above Ra = 1e11 in their experiments. This phenomenon has not been observed in other laboratories. Using our newly developed cylindrical convection cell of variable aspect ratio G with very thin stainless steel wall is well suited to resolve this issue as well as remaining controversy about the Nu(Ra,Pr,G) dependence.
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Návrh héliového kryostatu pro studium turbulentní tepelné konvekce při kryogenních teplotách
Srnka, Aleš ; Hanzelka, Pavel ; Musilová, Věra ; Urban, Pavel ; Skrbek, Ladislav
We present the design of a cryostat with an experimental cell for turbulent thermal convection using cryogenic helium gas. It is based on our long-term experience in cryostat design, especially low-loss cryostats for NMR magnets. The top and bottom of the convection cell are made of thick Cu plates. The cylindrical stainless steel wall consists of three parts; the middle one is exchangeable and allows for varying the cell aspect ratio. Another goal of our cell design is reduction of the parasitic heat flux from the copper plates via the cylindrical wall to its interior. As the cell operates up to 3.5 bar, we have paid significant attention to the safety of the cryostat and simulated critical situations such as a sudden vacuum loss.
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