Tortuosity studies of cellular vitreous carbon foams

The tortuosity of cellular vitreous carbon (CVC) foams having different bulk densities and different pore sizes has been investigated by a diffusion technique. The corresponding values were compared to tortuosities determined by two other different methods: acoustic on one hand, and tomographic on the other hand. Whereas acoustic tortuosities were slightly higher than diffusional ones but followed the same linear increase with CVC density, geometrical ones were much lower and presented the opposite trend. Such apparent discrepancies were discussed and justified, and the concept of constrictivity was used for that purpose. As diffusional tortuosity is the relevant parameter for accounting for transport phenomena, the permeability of CVC foams could be calculated from such tortuosity values, based on a realistic pore model of cellular carbon foams. The agreement between calculated and measured permeabilities was quite satisfactory.