Fractal Characteristics for Goose Down Assemblies as Porous Media

In this paper, the fractal characteristics of goose down assembly are described by determining the pore area fractal dimension and the tortuosity fractal dimension. The goose down assembly, filled with mass of down fibers and pores, is loose and ductile. The pores are varying shapes and sizes, and distribute unevenly. Firstly, micro computed tomography is used to observe the internal microstructure of down assembly without destructing the original assembly shape. The derived computed tomography images of down assemblies with various volume fractions are then treated by two-value method. The measurement verifies that the porous structure of down assembly possesses typical fractal characteristic, and the pore area fractal dimensions Df are determined by the box counting method. According to the capillary principle the tortuous flow path in down assembly is simulated, and the fractal dimension of the tortuous flow path DT is also calculated by the same way. The results indicate that the pore area fractal dimensions decrease and the tortuosity fractal dimensions increase gradually as the volume fractions Vf of the assembly increase.