A Fractal Model for VOCs Diffusive Transport in Dry Porous Building Materials

摘要

In order to study the effect of microscopic structure characteristics on the VOCs diffusive transport in building materials, a fractal model is developed and analyzed to investigate the mass transfer characteristics of VOCs diffusive transport in dry porous building materials. The classical Fick's diffusion law is extended to a fractal diffusion model in this work. Using the method of separation variables, the theoretical solution of VOCs fractal diffusion model in a porous structure is obtained. Combined with the microscopic structure characteristics, the VOCs diffusion process in dry porous building materials is simulated by using different surface fractal dimensions and fracton spectral dimensions. The simulated results show that the surface fractal dimensions and fracton spectral dimensions exhibit different effects on the VOCs migration process in dry porous building materials. The increase of the surface fractal dimension demonstrates the increase of specific surface area. The fracton spectral dimension affects the VOCs diffusive transport remarkably in the early stage, but the distinction between different hysteresis effects caused by different fracton spectral dimensions is becoming increasingly small with respect to the diffusion time. Both the surface fractal dimensions and fracton spectral dimensions reflect the influence of fractal structures on VOCs diffusive transport. Combining the surface fractal dimensions with fracton spectral dimensions provides a farther interpretation for the VOCs diffusion process in dry porous building materials.