Fractal diffusion of VOCs in dry porous building materials

For the purpose of clarifying the influence of microscopic structural characteristics on the diffusive transport of volatile organic compounds (VOCs) in building materials, many researchers have proposed different models to predict the diffusion process based on the micro-structure analysis. In this study a fractal model was developed and analyzed to investigate the mass transfer characteristics of VOCs’ diffusive transport in dry porous building materials. The classical Fick’s diffusion law was extended to a fractal diffusion model. Using the method of separation of variables, the theoretical solution to a fractal diffusion model of VOCs in a porous structure was obtained. Combined with microscopic pore structure characteristics, the surface fractal dimensions of medium density fiberboards (MDFs) used for building decoration were evaluated by using the experimental results of mercury intrusion porosimetry (MIP). The diffusion process of VOCs in dry porous building materials was simulated by using different surface fractal dimensions and fracton spectral dimensions. Simulated results showed that the surface fractal dimensions and fracton spectral dimensions exhibit different effects on the migration process of VOCs in dry porous building materials. Both the surface fractal dimensions and fracton spectral dimensions reflect the influence of fractal structures on diffusive transport of VOCs. Combining the surface fractal dimensions with fracton spectral dimensions provides a novel interpretation for the diffusion process of VOCs in dry porous building materials.