Abstract:Based on the Area-Perimeter Method, the fractal theory and the experiment results of free settling, the profile fractal dimensions of the free settling particles in air are calculated. Using optical microscope, the grain projection images of air particles are obtained. With an image analysis software, the grain shape of air particles and the relation between the profile fractal dimension and the settling time are obtained. An analysis is made for air particles with consideration of the special causes of their formation. It is shown that the grain shape of air particles exhibits a distinct fractal characteristic, which is getting more distinct when the grain is smaller. The profile fractal dimensions of the particle range from 0.869 to 1.048. The value of fractal dimension decreases with the increase of the sampling time, and the fractal characteristic is getting less distinct. It is found that the higher percentage of finer particles is associated with the higher profile fractal dimension value of particles. This quantitative description of the profile fractal distribution of free settling particles in air, provides a new way to predict the shape change of the grain and the adhesion force between particles.