Heat Transfer in Microsphere Insulation in the Presence of a Gas
Evacuated porous materials have seen wide use as cryogenic insulations for many years [1,2] and numerous studies [2–9] have addressed the technology of heat transport in these powder, fiber, foam and multilayer types of insulation. Although they are comprised of a wide variety of materials, the mechanisms of heat transfer by radiation and solid conduction within the media are well understood. However, when a fluid is present in the void spaces between and/or within particles the heat transport is less well defined, particularly at cryogenic temperatures and in the pressure range intermediate to free molecular and continuum regimes [10–12].
KeywordsHeat Transfer Knudsen Number Solid Conduction Cryogenic Engineer Apparent Thermal Conductivity
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