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Making thin and out of thermally nonconductive

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Unformatted text preview: The connection to the outer shield, or pressure vessel, is thermally weak (though mechanically strong) – G-10 fiberglass is good for this purpose • Ordinary radiative coupling of ( Th4 few W/m2 – minimized by making thin and out of thermally nonconductive material – Gold plating or aluminized mylar are often good choices – bare aluminum has 0.04 – gold is maybe 0 .01 • Radiation is left, but suppressed by making all surfaces low emissivity (shiny) • Heat paths cut holds holds temperature of fluid Winter 2008 Tc4) = 415 W/m2 is cut to a is – aluminized mylar wrapped in many layered sheets is common (MLI: multi-layer insulation) – MLI wants to be punctured so-as not to make gas traps: makes for slooooow pumping 17 Winter 2008 18 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 Dewar Construction cryogen port Cryogen Lifetime perforated G-10 cylinder cryogen (LN2 ) tank science apparatus inner shield vacuum port • Cryogen is isolated from warm metal via G-10 – but in good thermal contact with inner shield • Metal joints welded • Inner shield gold-coated or wrapped in MLI to cut radiation • Windows have holes cut into shields, with vac...
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