Modeling of soot particle collision and growth paths in gas-solid two-phase flow

Abstract

Particle collision is an important process in soot particle growth. In this research, based on gas-solid two-phase flow, particle trajectory was traced by the Lagrange approach with periodic boundaries. Trajectory intersection, collision probability, and critical velocity were considered, and the growth path of each particle was traced. The collision frequency, fc, agglomeration frequency, fa, and friction collision frequency, ffc, were calculated, and the main influence factors of particle collision were analyzed. The results showed that fc, fa, fa/fc increased with the increase of the particle volume fraction and gas phase velocity, v, but the particle initial diameter, dpi, and velocity had the great influence on fa/fc. fa/fc obviously decreased with the increase of dpi and v. The statistical analysis of fa/fc and Stokes number showed that fa/fc decreased with the increase of Stokes number, especially when Stokes number was extremely small, fa/fc decreased rapidly. Using the trajectory analysis of each particle, the particle growth process could be classified in three types: firstly, the particles that did not agglomerate with any particles during the entire calculation process, secondly, the particles that continually agglomerated with small particles to generate larger ones, and finally, the particles that were agglomerated by larger particles at some calculation moment.