Flame Propagation in Bimodal Nano/Micro-Sized Aluminum Particles/Air Mixtures

The evaporation and combustion of nanometric aluminum particles with an oxidizer MoO3 is analyzed. The analysis was performed to correlate individual Al particle gasification rates to macroscopic flame propagation rates observed in flame tube experiments. Examination of various characteristic times relevant to propagation of a deflagration reveals that particles below about 1.7 nm in diameter evaporate before appreciable chemical reactions occur. Experimental studies use Al particles greater than 1.7 nm in diameter such that a diffusion flame model was developed to better understand the combustion dynamics of multiphase Al particles. The results showed that it is unlikely that droplets will fully evaporate before reacting in the gas phase. A droplet evaporation and combustion model was further applied to quantify single droplet reaction velocities in comparison to the bulk flame propagation measurements observed in the literature. The diffusion flame model predicted orders of magnitude slower propagation rates than experimentally observed. These results imply that another reaction mechanism is responsible for promoting reaction propagation or modes other than diffusion play a more dominant role in flame propagation.

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Flame propagation through dust clouds of nano and micron scale aluminum particles

Journal of Loss Prevention in the Process Industries ◽

10.1016/j.jlp.2020.104266 ◽

2020 ◽

Vol 68 ◽

pp. 104266

Author(s):

Po-Jul Chang ◽

Toshio Mogi ◽

Ritsu Dobashi

Keyword(s):

Flame Propagation ◽

Aluminum Particles ◽

Dust Clouds

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Experimental Investigation on Quenching Distance for Aluminum Dust Flames

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2008-55006 ◽

2008 ◽

Author(s):

M. R. Habibzadeh ◽

M. H. Keyhani

Keyword(s):

Experimental Investigation ◽

Flame Propagation ◽

Oxygen Transport ◽

High Speed ◽

Steel Plates ◽

Aluminum Particles ◽

Lean Limit ◽

Dispersion Technique ◽

Quenching Distance ◽

Upper Third

An experimental investigation on quenching distance for Al dust flames have been done in improved flow system which can yield stable, controlled, and uniform dust mixtures. Experiments were performed with 18 micron aluminum particles diameter. Dust dispersion technique uses an annular high-speed jet which disperses dust continuously supplied via a piston-type dust feeding system. Laminarized dust flow ascending in a vertical Pyrex tube (d = 4.6cm, L = 150cm) was ignited at the open tube end. Constant pressure flames propagating downwards were observed. A set of thin, evenly spaced steel plates was installed in the upper third part of the tube in order to determine the flame quenching distance. Three different stages of flame propagation were observed: laminar, oscillating (transition region), and turbulent accelerating flames. Quenching distance as a function of dust concentration were determined during the laminar stage of flame propagation in dust-21% Oxygen-79% Nitrogen, dust-30% Oxygen-70% Nitrogen, and in dust-21% Oxygen-79% Argon mixtures. Furthermore, this research studies the effects of bed-gas on quenching distance and lean limit of combustion. It was found that the minimum quenching distance decreases when concentration of oxygen increases in the mixture. The minimum quenching distance is found to be about 4mm in air and decreases to 2mm in mixture of 30% O2. Also, it was found that the amount of lean limit of combustion decreases with increasing of oxygen percentage in mixture. The substitution of Argon for Nitrogen in air decreases the minimum quenching distance from about 4 to 3mm, and the amount of lean limit of combustion increases. The results is discussed with a mechanism of diffusive oxygen transport to the surface of burning Al particles in which a higher rate of oxygen transport in the N2/O2, as compared to the Ar/O2 gas mixtures.

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