A two-step simulation methodology for modelling stagnation flame synthesised aggregate nanoparticles

Abstract

A two-step simulation methodology is presented that allows a detailed particle model to be used to resolve the complex morphology of aggregate nanoparticles synthesised in a stagnation flame. In the first step, a detailed chemical mechanism is coupled to a one-dimensional stagnation flow model and spherical particle model solved using method of moments with interpolative closure. The resulting gas-phase profile is post-processed with a detailed stochastic population balance model to simulate the evolution of the population of particles, including the evolution of each individual primary particle and their connectivity with other primaries in an aggregate. A thermophoretic correction is introduced to the post-processing step through a simulation volume scaling term to account for thermophoretic transport effects arising due to the steep temperature gradient near the stagnation surface. The methodology is evaluated by applying it to a test case: the synthesis of titanium dioxide from titanium tetraisopropoxide (TTIP) precursor. The thermophoretic correction is shown to improve the fidelity of the post-process to the first fully-coupled simulation, and the methodology is demonstrated to be feasible for simulating the morphology of aggregate nanoparticles formed in a stagnation flame, permitting the simulation of quantities that are directly comparable to experimental observations.

Modelling soot formation in a benchmark ethylene stagnation flame with a new detailed population balance model

“…A similar two-step simulation methodology has been used successfully to simulate soot formation in laminar premixed flames without a stagnation surface [36]. In this work, an improved post-processing method proposed by Lindberg et al [48] which is capable of accounting for thermophoretic transport effects is employed to perform the population balance simulations. More detailed discussion on the two-step methodology used in this work may be found in [48].…”

“…In this work, an improved post-processing method proposed by Lindberg et al [48] which is capable of accounting for thermophoretic transport effects is employed to perform the population balance simulations. More detailed discussion on the two-step methodology used in this work may be found in [48].…”

“…If the coordinates of primary particles are not tracked, an assumption about the fractal dimension of the aggregates is required to derive their simulated mobility diameters. In addition, thermophoretic transport effects were overlooked in the post-processing step of previous study [37], yet should be accounted for as the temperature gradient is steep near the stagnation plate [48].…”

“…A smoothing factor, which was introduced into the old model to account for particle rounding due to mass growth [25,36], is no longer needed in the new model as the particle morphology is known. Thermophoretic transport has been accounted for in the post-process by introducing a modified simulation volume scaling term [48]. A thorough sensitivity study is carried out to understand how the model parameters effect the computed PSDs.…”

Numerical Study of Single Iron(III) Nitrate Nonahydrate/Ethanol Droplet Evaporation in Humid Air

“…Spray flame synthesis of functional nanoparticles is a very promising method to produce nanoparticles with special characteristics. While the synthesis of nanoparticles in gas flames is well established, for instance for the production of fumed silica [1] and carbon black [2], flame spray pyrolysis (FSP) has been studied to a lesser extent. FSP is characterized through processes including the heating, evaporation, and transformation of the precursor solution into the gas phase and the combustion of the resulting system as well as the formation of the nanoparticles.…”