Research On Particle Dispersion In Turbulent Channel Flows And Its Application For Electrostatic Precipitator

Fluid-particle two-phase turbulent flows are closely related with energy, chemical industry, hydraulic engineering, environment, and other industrial fields in the national economy. In the past 30 years, a lot of research accomplishments on fluid-particle two-phase turbulent flows have been achieved, but the researches of fluid-particle two-phase flows in shear turbulence near wall are yet not sufficient, and the theoretical researches of which in engineering application are more limited.In the present paper the particle dispersion in two-phase turbulent channel-flow is studied with direct numerical simulation (DNS), on the base of which the aggregation properties of particles are analysed in electrostatic precipitator. The research begins with the simulation of a single-phase turbulent channel-flow, and the turbulence characteristics of two-dimensional (2-D) channel are analysed. Then the particle dispersion with particle Stokes number Stk of 0.01,1.3 and 11.4 is studied in fluid-particle two-phase turbulent channel-flow with Reynolds number (Re) of 5500. At last the aggregation properties and collection efficiency of particles in flows and electric field in electrostatic precipitator are studied.The 2-D turbulent channel-flow is simulated directly with pseudo-spectral method, and the solving methods of streamwise and spanwise velocities in the spectral space are improved, which saves the computing resource obviously. The statistical results of turbulence are consistent with the predecessor's achievements.The two-point correlation results of wall shear stress and near-wall vorticity indicate that the wall shear stress is associated with the near-wall vortices and the maximum correlation-value locations of the near-wall vortices are 0.03 and 1.2 (scaled with half-width of channel). The evolutionary process of vortices indicates that an obvious self-organization of vortices exists in 2-D turbulent channel-flow, and inverse energy transfer from small scale structures to larger ones is along with the self-organization process.The statistical results of fluid-particle two-phase turbulent channel-flow indicate that the velocity of particles is stable but the concentration is unstable. The concentration of particle increases gradually from the centre to the wall, which shows preferential concentration near wall in wall shear two-phase flows. The effection on mean motions of particle by particle inertia is mainly in the near-wall region. The laws of particle preferential concentration at different locations away from the wall are different. The particle preferential concentrations are more obvious with the location closer to the wall when the Stk is 0.01. When the Stk is 1.3 and 11.4, the particle preferential concentrations are most obvious at the location between 0.4 and 0.8 away from the wall.Based on the fluid-particle two-phase turbulent channel-flow, the particle dispersion and collection efficiency are studied with the fluid drag and electric field force in industrial electrostatic precipitator. The instantaneous distribution and motion curves of particle show that with the same Stk, the particle preferential concentration is more obvious near the wall with the increase of applied voltage. In the initial stage, when the applied voltage is larger, the value of transverse diffuse function is larger, and the transverse motion of particles is also more obvious. With the same Stk, the particle collection is more efficient if the applied voltage is larger; while with the same applied voltage, the particle collection is also more efficient if the Stk is larger.The research in this paper has contributed to understand the particle dispersion in wall shear turbulence and provides guidance for its application in industrial electrostatic precipitator, and laies the foundation of the study for the fluid-particle two-phase flows in coupled multi-physics in the future.