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LITERATURE REVIEW: HEAT TRANSFER THROUGH TWO-PHASE INSULATION SYSTEMS CONSISTING OF POWDERS IN A CONTINUOUS GAS PHASE
Citation:
Yarbrough, D. LITERATURE REVIEW: HEAT TRANSFER THROUGH TWO-PHASE INSULATION SYSTEMS CONSISTING OF POWDERS IN A CONTINUOUS GAS PHASE. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-92/203 (NTIS DE93014387), 1993.
Description:
The report, a review of the literature on heat flow through powders, was motivated by the use of fine powder systems to produce high thermal resistivities (thermal resistance per unit thickness). he term "superinsulations" has been used to describe this type of material, which has thermal resistivities in excess of 20 sq ft- h- F/Btu (3.52 K. sq m/W) per in. (2.54 cm) of insulation thickness. .he report is concerned with superinsulations obtained using evacuated powders. he literature review shows that the calculation of heat flow through gas-powder systems is highly developed. ne major weakness in the calculated procedures is the absence of structural features for the powders, which are invariably characterized as regular arrays of spheres or cubes, rather than random irregularly shaped particles. he effect of particle size distribution on the shape and size of void spaces is not modeled, although it affects the thermal conductivity of the gas. alculations of thermal performance based on simplified descriptions of the porosity distribution can be used to show the dependence of thermal resistance on interstitial gas pressure. he literature reviewed in this report provides a basis for predicting the interstitial gas pressure at which thermal conductivity begins to increase. he objective is to design filler material for powder insulation systems with ultrafine void spaces.
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LITERATURE REVIEW: HEAT TRANSFER THROUGH TWO-PHASE INSULATION SYSTEMS CONSISTING OF POWDERS IN A CONTINUOUS GAS PHASE