Mais informações

Serkitjis, Mihail Mihail; Hagentoft, Carl-eric Carl-eric. The Influence of Natural Convection on the Heat Transfer in an Air Filled Porous Medium Bounded by an Air Layer. Nordic Journal Of Building Physics: Acta Physica Aedificiorum, p. 1 -2, 1998.
Clique no nome do(s) autor(es) para ver o currículo Lattes:

Dados do autor na base InfoHab:
Número de Trabalhos: 1 (Nenhum com arquivo PDF disponível)
Citações: Nenhuma citação encontrada
Índice h: Indice h não calculado  
Co-autores: Nenhum co-autor encontrado

Dados do autor na base InfoHab:
Número de Trabalhos: 3 (Nenhum com arquivo PDF disponível)
Citações: Nenhuma citação encontrada
Índice h: Indice h não calculado  
Co-autores: Nenhum co-autor encontrado

Abstract

A numerical and experimental study is performed to analyze the influence of natural convection on heat transfer in a composite system comprising a porous material heated from below and an air space situated above this. The numerical model is verified by conducting a number of experiments, on a model material consisting of polystyrene pellets of cylindrical shape, made in the Wind Box. This apparatus is a prototype and has been designed and developed at the Department of Building Physics. In designing the measuring process, calculation of the maximum systematic error has been a control parameter; this is less than 6%. The study includes measurements in the Wind Box and calculations with a recently developed simulation program (CONVBOX) for three-dimensional convection problems. The combination of simulation and experiments performed in the Wind Box has been found to be an important instrument in understanding the complex coupled convection processes which occur in the insulation material. The agreement between the calculations and the experimental results is, in general, good. Influence of the ratio between the thicknesses of the air space and the porous medium was studied in terms of Nusselts number and the temperature difference across the composite system and the porous material. The following can be stated on the basis of the calculations and measurements: - Occurrence of natural convection in the air space has only a marginal effect on heat transfer in the underlying porous media. - The thermal resistance of the air space may be assumed constant, which means that in theoretical models the air space can be replaced by a constant thermal resistance. - Alteration of the boundary condition at the interface between the thermal insulation and the air layer from a covered to an open top surface halves the critical modified Rayleigh number from 40 to 20. - The ratio between the thicknesses of the air space and the thermal insulation has no critical significance for the heat transfer. It may be considered that the available data regarding the validity of the theoretical model are of limited extent for an assessment to be made whether it can be applied more generally. From the comparisons of calculations with measurements on polystyrene pellets, it is evident that the theoretical model holds for this material. It is possible that the geometry of the material may have some influence, which means that the model ought to be tested on other porous materials, such as anisotropic fibrous materials.
-