Nanoparticle Coagulation in a Planar Jet

Abstract

Direct numerical simulation of nanoparticle coagulation in a planar jet is performed. The particle field is represented using a sectional method to approximate the aerosol general dynamic equation. The methodology is advantageous in that there are no a priori assumptions regarding the particle size distribution and coupled with an unsteady Navier-Stokes solver, it provides the spatiotemporal evolution of the particle field in an accurate manner. The jet consists of an incompressible fluid containing particles 1 nm in diameter issuing into a particle-free coflowing stream. Ten sections are solved allowing the particle field to develop to 8 nm in diameter. Results show that the geometric standard deviation reaches the self-preserving value within one jet diameter downstream of the nozzle and remains at that value up to 7.5 jet diameters. In this proximal region, the particle size is relatively uniform throughout the jet. Further downstream, the effects of large-scale vortical structures is to increase the residence time of particles within the domain and perturb the geometric standard deviation beyond the self-preserving value.

Large Eddy Simulation of Titanium Dioxide Nanoparticle Formation and Growth in Turbulent Jets

“…As the flow develops, the reactants are converted to TiO 2 , particles nucleate, collide/coagulate, grow and therefore move from lower-numbered to higher-numbered bins. Additionally, particles are dispersed and transported from the particle-laden stream to the particle-free stream due to the effects of convection and diffusion (Modem et al 2002;Moody and Collins 2003;Miller and Garrick 2004;Garrick et al 2006;Wang and Garrick 2005). In this work, our focus is on the qualitative and quantitative differences between results obtained via LES and those obtained via DNS as they pertain to assessing the performance of the LES approach.…”

“…In this work, our focus is on the qualitative and quantitative differences between results obtained via LES and those obtained via DNS as they pertain to assessing the performance of the LES approach. Descriptions of the dynamics of nanoparticle growth in shear flows are available elsewhere (Modem et al 2002;Miller and Garrick 2004;Settumba and Garrick 2007).…”

“…There have been recent efforts towards the simulation of nanoparticle dynamics in turbulent flows. These include both DNS as well as other modeling approaches (Settumba and Garrick 2003;Miller and Garrick 2004;Wang and Garrick 2005;Garrick et al 2006;Settumba and Garrick 2007;Das and Garrick 2010). These have been useful in illustrating, for example, the dynamics of nucleation, condensation, and coagulation under a variety of flow conditions.…”

Effects of Turbulent Fluctuations on Nanoparticle Coagulation in Shear Flows

“…The coagulation Damköhler number is the nondimensional particle coagulation rate (Settumba and Garrick 2003;Miller and Garrick 2004). PDFs of SGS conditioned on the scalar dissipation, for cases 2 and 3, Da = 1 and Da = 2 are shown in Figures 6 and 7, respectively.…”

“…The coagulation of nanoparticles in shear flows-both temporally developing and spatially developing-has been the subject of exposition and is not the primary focus in this work (Modem et al 2002;Settumba and Garrick 2003;Miller and Garrick 2004;Settumba and Garrick 2004). However the evolution of the first moment is shown here to illustrate (a) the growth of the eddies, (b) the large-scale mixing of the particlefree and particle-laden streams, and (c) an important property of three-dimensional flows entirely absent in two-dimensional flows-vortex bending and stretching.…”