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Combustion and Reactive Flows

Controlling Gravity Impact on Diffusion Flames by Magnetic Field

[+] Author and Article Information
Fouad Khaldi

 SIMAP-EPM-Madylam/CNRS, ENSHMG, BP 95St. Martin d’Hères Cedex, Grenoble 38402, Francefouadkhaldi@gmail.com

J. Heat Transfer 134(6), 061201 (May 02, 2012) (5 pages) doi:10.1115/1.4006011 History: Received January 18, 2011; Revised October 13, 2011; Published April 30, 2012; Online May 02, 2012

The ability to use a magnetic field as a means for controlling the role of gravity buoyancy on the combustion process is demonstrated by applying a strong vertical magnetic field gradient on a laminar gas jet diffusion flame. The confirmation is based on a comparison of flame appearance; in particular, length variation, to both elevated gravity (higher than earth’s gravity) and zero-gravity combustion experimental data. The comparison parameter is the dimensionless number G, defined as the ratio of gravity level generated by magneto-gravity buoyancy to earth’s gravity. The more important results are as follows. First, for G > 1, good agreement between magnetic and centrifuge length scaling laws reveals that the slight decrease of flame length according to L ∼ G−1/8 is the result of increasing artificial magnetically induced gravity strength. It ensues that flame thinning, bluing, lifting, and extinction are produced by similar mechanisms previously identified in centrifuge diffusion flames. Thereafter, at G ≅ 0, the flame assumes a nearly hemispheric shape and a blue color in perfect similarity to nonbuoyant flames under zero-gravity conditions generated in drop towers. Another important fact is that the magnetic field offers the ability to observe the flame behavior at low gravity levels 0 < G < 1. A primary interesting result is that flame length varies strongly, following the scaling law L ∼ G−1/2 .

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup

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Figure 2

Distributions of magnetic field intensity and magnetic field gradient intensity along the axis of the magnet

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Figure 3

Images of a propane flame at various values of BdB/dz (T2 /m) (first line) and G (second line)

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Figure 4

Flame length, L, normalized to burner diameter, d, and Reynolds number, Re, versus gravity level, G

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Figure 5

Appearance comparison between magnetically and drop tower nonbuoyant flames: (a) Present study and (b) Sunderland

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