• Numerical Study of Silica Particle Formation in Turbulent H2/O2 Flame

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This week a new paper has been published in the IFRF Combustion Journal (http://www.journal.ifrf.net), entitled:

“Numerical Study of Silica Particle Formation in Turbulent H2/O2 Flame”

A. Pitkänen, J. M. Mäkelä, M. Nurminen, A. Oksanen, K. Janka, J. Keskinen, H. Keskinen, J. K. Liimatainen, S. Hellstén  and T. Määttä


Anna Pitkänen
Tampere University of Technology
Power Plant and Combustion Technology
P.O. Box 589
FIN-33101 Tampere

Tel  358-40-563 5907
Fax  358-3-3115 3751
Email anna.pitkanen@tut.fi

This paper discusses silica particle formation in a turbulent flame. This has application for the manufacture of ceramic commodities such as pigmentary titania, fumed silica, alumina, optical fibers and ultra-fine nano-particles. The authors apply computational fluid dynamic modeling to estimate the spatial distribution of the particle formation for improving the in-flame collection of nanoparticles. Predicted results compare well with published data.

In this paper, silica particle formation in a turbulent flame was studied. Micron sized spray droplets from liquid tetra-ethyl-ortho-silicate were introduced into a turbulent hydrogen-oxygen flame with a patented Liquid Flame Spraying technique. In this technique, the spraying gas is one of the reactant gases, and in this particular study hydrogen was used. In the flame, the liquid precursor evaporates and reacts in gas phase. The chemical product is finally nucleated generating nanosized silica powder. The purpose of the study was to estimate the spatial distribution of the particle formation for improving the in-flame collection of nanoparticles in commercial applications, where subsequent particle agglomeration needs to be avoided. To achieve that, a simple but effective method for approximating the nucleation of silica vapour was utilised. Results show, that within the turbulent diffusion flame, there is a spatial zone of high temperature with under-saturated silica vapour. This high temperature zone is first following by a region where liquid nanoparticles are generated, then a region where solid silica particles are formed. In conventional laminar diffusion flames with lower temperatures, solid silica particles are directly generated from the silica gas. In our case, the liquid nucleation stage may be described with the classical nucleation theory, but the overall model fails to convert all the silica vapour into particulate form.  Therefore, in a large scale it is insufficient and needs compensating modelling of full aerosol dynamics, including barrierless nucleation kinetics, condensation, coagulation, coalescence and particle agglomeration. Another approach is to use a simple equilibrium model based on a constant value for critical saturation ratio for particle forming vapour. However, even with this simpler tool, the on-set of particle formation was probed. The model showed that the particle formation begins before the actual flame region, is interrupted in the high temperature zone but subsequently continues after the hottest part of the flame. The result was verified in the experiments.

Key Words:
Modelling, silica, nanoparticle generation, nucleation

The full paper may be downloaded from the server, in the “New Papers” section (http://www.journal.ifrf.net/articles.html), by clicking on the Acrobat PDF icon alongside the title.

Publication in the Journal
As Editor-in-Chief I would like to remind all potential authors that publication in the Journal is open to all. If you have interesting results to publish in the field of, or related to, industrial combustion, we invite you to prepare a paper according to the guidelines given in the Author’s Guide on the website (http://www.journal.ifrf.net/).

Papers may be regular “articles” (typically up to 20 pages) or Communications (typically up to 4/5 pages). Review papers can of course be longer. Remember that figures and graphics in general can be in full color. This advantage should be encouraged.

All manuscripts and associated files, proposed for publication should be sent by the Corresponding Author in a compressed/zip file, as an email attachment to journal@ifrf.net. This file should include a statement that the proposal’s content is unpublished material that has not being submitted for publication elsewhere. When an article by the author(s) is cited in the proposed article as “in press”, a copy of this article should accompany the proposed article and should be included in the compressed file.

I look forward to receiving your proposals.