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THERMAL CONDUCTIVITY OF OPEN- AND CLOSED-CELL FOAMS: INFLUENCES OF CELL RANDOMNESS

Jaona Harifidy Randrianalisoa
Centre de Thermique de Lyon, Institut National des Sciences Appliqués, Lyon; GRESPI - EA 4694, University of Reims Champagne-Ardenne, F-51687 Reims, France

Remi Coquard
Société "Etude Conseils Calcul Modélisation" (EC2-MODELISATION), 66 Boulevard Niels Bohr, F69603 Villeurbanne, France

Dominique Baillis
LaMCoS, INSA-Lyon, CNRS UMR 5259,18-20 Rue des Sciences, F69621 Villeurbanne, France

Аннотация

The effects of cell randomness and sample size on thermal conductivity of cellular foams were investigated through finite-element method (FEM) applied to numerical samples generated by the perturbed Voronoï diagram. The 3D aspect of foam materials, the nature of the cells (open or closed), the distribution of cell size, and the randomness of the cell shape and location were taken into account. For model validation, a comparative study with experimental and existing numerical results of open-cell (metallic and ceramic) and closed-cell (polymer) foams was carried out. The limited size of samples leads to an under or overprediction of the thermal conductivities of cellular foams depending on the cell nature. The size effects are notably due to the non-uniformity of small and large volume porosity (or relative density) having identical cell wall thickness or strut cross-section area. These effects become negligible when samples, the representative elementary volume (REV), contain tens of cells along each volume side. The cell randomness (in term of shape and location), captured here through the cell size standard deviation of Gaussian-normal distribution, results in an increasing of the material turtuosity and consequently a decreasing of the foam thermal conductivity. The effects are more important for open-cell structures than for closed-cell structures. The proposed approach predicts perfectly the numerical results of volume-finite method applied to tomographied foams. Its suitability for modeling thermal conductivity of both open- and closed cell foams is confirmed by the agreement between calculations and measurements in wide temperature and porosity ranges.

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