Thermal conductivity cryogenic solids

Discontinuities in the lattice such as vacancies, impurities, or grain boundaries also act to scatter phonon propagation, hence a lower thermal conductivity is expected in solids containing these defects at cryogenic temperatures. Whichever mecha-... 

The chemical and physical properties of each of these window materials vary widely. For example, polyimide is flexible, semitransparent, and chemically inert, but it has an upper working temperature of 673 K (for information about the properties of Kapton see http //www2.dupont. com/Kapton/en US / assets / downloads / pdf/ summaryofprop.pdf). Beryllium is stiff, has a low density, high thermal conductivity, and a moderate coefficient of thermal expansion it can be machined and is very stable mechanically and thermally. It also retains useful properties at both elevated and cryogenic temperatures. However, it does require a few safety-related handling requirements that are well documented (for detailed environmental safety and health information about beryllium see http //www.brushwellman.com). Nonetheless, as is stated in the Brush Wellman literature (for detailed environmental safety and health information about beryllium see http //www.brushwellman.com), "handling beryllium in solid form poses no special health risk."... 

In order to maintain adequate lubrication, the wear rate of the lubricant must be controlled when it is introduced as a solid at the interface, where its properties and those of the cryogenic liquid will be influenced by the much higher temperature and vapor phase conditions which exist at this point. The over-all heat transfer, and therefore the interface temperature, depends on a considerable number of factors, with thermal conduction paramount. Since a solid lubricant with poor thermal conductivity is desirable for tensile property reasons, arrangements must be made elsewhere in the lubricant housing and the mating components favorable to good therm.al conductivity. 

Valalaki K, Nassiopoulou AG (2013) Low thermal conductivity porous Si at cryogenic temperatures for cooling applications. J Phys D Appl Phys 46 295101-295109 Wolf A, Brendel R (2006) Thermal conductivity of sintered porous silicon films. Thin Solid Films 513(l-2) 385-390... 

At cryogenic temperatures, two assumptions can be made to simplify this expression (1) the term containing is usually small relative to the term containing kg and normally can be neglected and (2) the thermal conductivity of the solid material, k, is much larger than the thermal conductivity of the gas, k. Hence, Eq. (7.21) reduces to... 

The apparent thermal conductivity of a powder insulation is a function of the thermal conductivities of the powder and interstitial gas and the ratio of solid volume to total volume at cryogenic temperatures such that... 

Many experiments have been conducted in the past with cryogenic liquids, mostly LNG, LPG, or the non-hazardous LN2, to examine transient cryogenic pool behavior on both solid and liquid surfaces [e.g., 24, 25, 34, 38, 64, 65]. Main goals were the examination of the transient pool behavior under different release conditions on different surfaces and the verification of the thermal phenomena. Only a few data are available on LH2 pool behavior. 

Superinsulation, maximum-efficiency insulation, super-dewars, multiple-layer insulation, all of these terms denote the developments of insulating systems where the heat transfer mechanism of gas conduction, solid-to-solid conduction, and radiation have been reduced to a minimum. Although these insulations have been developed only recently, the methods used to reduce heat flow are not fundamentally new. Dewar demonstrated in 1898 that an evacuated space between two vessels, suitably silvered, forms an effective barrier by radiation-shielding the evacuated space. Smoluchowski, in his contribution to the kinetic theory of gases, showed in 1910 that thermal insulators more effective than air could be made from fine powders in a moderate vacuum. It is on the basis of the work of these scientists that further developments in insulation for cryogenic vessels have proceeded. 

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