Abstract
This work is a first direct numerical simulation of a configuration closely related to the SpraySyn burner (Schneider et al. in Rev Sci Instrum 90:085108, 2019). This burner has been recently developed at the University of Duisburg-Essen to investigate experimentally nanoparticle synthesis in spray flames for a variety of materials. The present simulations are performed for ethanol and titanium tetraisopropoxide as a solvent and precursor, respectively, in order to produce titanium dioxide nanoparticles. In the direct numerical simulations, the complete scenario leading to the production of well-defined nanoparticles is taken into account, including evaporation of the liquid mixture (solvent and precursor) injected as a spray, multi-step kinetics for gas-phase combustion, and finally nanoparticle synthesis. The employed models are described in this article. Additionally, the impact of the inlet velocity of the pilot flame on the nanoparticle synthesis is investigated. It has been found that increasing this speed delays spray flame ignition, decreases nanoparticle concentration, but leads to a narrower size distribution at early stage.
Highlights
Nanoparticles are found in many environmental processes and in an increasing number of industrial applications
Since the present DNS simulations consider only a small part of the whole SpraySyn burner plenum, all effects that may occur further downstream cannot be captured. These DNS results depict the initial part of the process, starting with the injection of the very first spray droplets, leading later to spray flame ignition; the simulation is stopped when the remaining spray droplets start leaving the DNS domain through the top outflow
These results indicate that the inlet velocity of the pilot flame could be used as well as a control parameter to drive the resulting PSD
Summary
Nanoparticles are found in many environmental processes and in an increasing number of industrial applications. The focus is currently set on nanoparticle synthesis from spray flames (Mädler et al 2002; Mueller et al 2003; Weise et al 2015; Rittler et al 2017) This is because the conventional gasphase processes (synthesis from a gaseous flame) require precursors that are either gaseous or that can be vaporized and mixed with the burner gases before they react within the reaction chamber. This burner shall deliver benchmark data for the corresponding research community (Schneider et al 2019). One of the advantages of this burner is that it is designed from the start while taking into account the bottlenecks of companion numerical simulations; for example, the gas feed for the pilot flame in this burner is injected through a thick porous area (flat flame), facilitating simulations since a very fine grid is not needed there
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