Particle behavior in the turbulent boundary layer of a gas-particle flow past a flat plate

Particle behavior in the turbulent boundary layer of an air-particle flow past a vertical flat plate was studied. A miniature fiber optic probe was developed to measure particle velocity and concentration in the boundary layer along a 1.5-m-long plate. Two size ranges of coal particles were used with mean diameters of 60 μm and 200 μm. The superficial air velocity was 20 m/s and 30 m/s, and solids loading ratio was varied between 0.3 and 1.2 (kg dust/kg air). Numerical simulations based on the Lagrangian and Eulerian approaches were carried out, using the commercial CFD code CFX-4.; The particle velocity measurements showed that particle mean velocity distribution inside the boundary layer follows the log law of the wall. The particle velocity is higher than the single-phase air velocity in the boundary layer and the boundary layer thickness of the particulate flow is smaller than that of the single-phase air flow. These effects are more pronounced as solids loading increases. The particle velocities of the 200 μm particles are higher than those of 60 μm particles due to greater inertia of larger particles. The numerical simulation confirmed that the particle velocity is higher than air velocity inside the boundary layer because of particle inertia, and particle velocity inside the boundary layer increases with the increase of solids loading. Momentum transfer from particles to air occurs inside the boundary layer and momentum exchanges between two phases and particle inertia explain both solids loading and particle size effects on particle velocity profiles as seen in the experimental results.; The experimental results also showed a non-uniform distribution of particle concentration with the peak concentration value inside the turbulent boundary layer. As the particle size increases, the particle concentration inside the boundary layer increases and the location of the peak value becomes much closer to the wall. This phenomenon is believed to be related to the slip-shear lift force (Saffman force) and particle-wall interactions.; Experimental measurements showed that properties of the wall surface material have effects on particle motion and distribution inside boundary layers. Particle-wall collisions play important roles in these effects.