A review on evolution characteristics of nanoparticles in gas-solid two-phase turbulent flow field

Abstract

The gas-solid two-phase turbulent flow with nanoparticles is very common in many fields including aviation. In the flow field, the nanoparticles, in the form of monomer and aggregate, undergo the processes of generation, convection, diffusion, coagulation and breakage, while the number density, scale and scale dispersion of particles will change. In this paper, we review the above research and draw the following main conclusions: Particle formation is caused by surface cooling, adiabatic expansion or mixing, turbulent mixing or supersaturation of condensable vapor produced by gas-phase chemical reaction; the causes of particle coagulation include Brownian motion, turbulent shear, velocity gradient and differential settlement; particle coagulation depends on particle size and flow field characteristics, and is controlled by initial particle distribution and turbulent diffusion; the influence of turbulence field on particle coagulation is not only the turbulence intensity, but also the fluctuation of particle number density caused by turbulence fluctuation; the agglomerates with large size formed after particle coagulation are easy to be broken under the action of flow shear and other factors; shear fracture is the main factor leading to particle breakage; and the effective breakage coefficient depends on the shear rate and the volume fraction of particles; the deposition of particles depends on the particle size, shape and fluid properties of particles; gravity, diffusion, inertial impact, electric field and heat transfer are the main factors leading to particle deposition; when there is a temperature gradient, the thermophoretic force also plays an important role in particle deposition. Finally, some problems are put forward for further studies.