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Titolo:
HEAT-TRANSFER BY CONDUCTION AND RADIATION IN BUILDING-MATERIALS - REVIEW AND NEW DEVELOPMENTS
Autore:
QUENARD D; CHEVALIER B; SALLEE H; OLIVE F; GIRAUD D;
Indirizzi:
SERV MAT,CTR SCI & TECH BATIMENT ST MARTIN DHER FRANCE
Titolo Testata:
Revue de métallurgie
fascicolo: 9, volume: 95, anno: 1998,
pagine: 1149 - 1158
Fonte:
ISI
Lingua:
FRE
Soggetto:
FOAM INSULATION; AEROGEL;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
18
Recensione:
Indirizzi per estratti:
Citazione:
D. Quenard et al., "HEAT-TRANSFER BY CONDUCTION AND RADIATION IN BUILDING-MATERIALS - REVIEW AND NEW DEVELOPMENTS", Revue de métallurgie, 95(9), 1998, pp. 1149-1158

Abstract

In the first part of this paper, the mechanisms of heat transfer through insulating materials are presented. Expanded PolyStyrene (EPS) foam is investigated in more details. As observed by optical an electron microscopy,: EPS exhibits a double-scale microstructure. It can be considered as a dense packing of cellular beads with three phases : the macropores between beads, the shell and the core of the pellets. Heat transfer is modelled taking into account conduction and radiation within cells and through cell-walls according to the model of Glicksman (1). Heat transfer through the packing of cellular pellets is described using the model of De Vries (2). Results taking into account the effectof foam density, cell-size and proportion of each phases are presented. The thermal conductivity of cellular materials exhibits an optimum value with regards to the cell sizes and the density. Actually as the cell struts act as barriers to radiation, when smaller cells are builtwith the same amount of polymer, the size of the struts are shrunk and they are no more efficient. The model of De Vries is also applied tolightweight concrete (Concrete + EPS beads). In the second part, heattransfer through a very low conductivity material is studied : monolithic organic aerogel. This material has a lower thermal conductivity than all other thermal insulants at ambient conditions (3) : around 0.023 W/mK without using any heavy gas. This low conductivity originates in : very high porosity (95 - 98 %) and thus small solid conductivity;extremely small pore size (10 - 100 nm lower than the mean free path of air), that causes a very low gaseous thermal conductivity due to Knudsen effect. Moreover, the gas conductivity can be minimized by lowering the gas pressure within the aerogel. A typical thermal conductivity of 0.008 W/mk can be reached at 0.05 hPa. At low temperature, the radiation is minimized and a value of 0.002 W/mK was obtained at 110 K and 0.05 hPa.

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Documento generato il 06/04/20 alle ore 02:14:37