Nanoparticle dispersion and coagulation in a turbulent round jet

Nanoparticle dispersion and coagulation behaviors in a turbulent round jet were studied in this article. An experimental system was designed to generate a uniformly distributed air–nanoparticle two-phase flow in a turbulent round jet. The particle size distribution (PSD) was measured by a scanning mobility particle sizer (SMPS) in the near field of the jet. The particle diameters were nearly constant in the potential core due to the high carrying velocity and laminar characteristic of the flow but grew larger in the region of high turbulence intensities because the vortex structures in the mixing layer promoted coagulation. Furthermore, the migration property of small-sized nanoparticles forced them to be preserved in the potential core also leading to the diameter increase. The comparison of the particle concentration distributions at different sections indicated that the shear layer is the major region for the mixing of particle-laden stream and ambient air. The particle diameters in the axial direction experienced three stages including a slightly changed stage, an increasing stage and a constant stage. The diameter increase should be attributed to turbulence coagulation.