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International Heat Transfer Conference 3

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

THE RADIATIVE PROPERTIES OF LUMINOUS FLAMES

M.W. Thring
Queen Mary College, London, England; Department of Fuel Technology and Chemical Engineering, University of Sheffield, England

J. M. Beer
Department of Fuel Technology and Chemical Engineering, University of Sheffield, England

P.J. Foster
Department of Fuel Technology and Chemical Engineering, University of Sheffield, England

DOI: 10.1615/IHTC3.1190
pages 101-111

Abstract

Observations of the radiation from industrial sized hydrocarbon-air turbulent diffusion flames provide empirical curves of flame emissivity and mean radiant temperature for, 1. High jet momentum oil/steam or gas flames. Control variables: fuel jet momentum, C/H ratio and molecular weight of the fuel, use of an oxygen jet. 2. Pressure jet oil flames; combustion air momentum and swirl. 3. Pulverised coal flames; primary air inlet velocity, coal fineness: and volatile content, secondary air velocity.
Measurements of soot concentration are compared with the luminous emissivities calculated from the soot concentration and the optical properties of carbon.
The Mie theory shows that for these particles (dp << λm mean radiation wavelength) the specific absorptivity of the soot dispersion is independent of D. This comparison gives agreement within a factor of about ± 30% for certain flames but for other flames the observed specific absorptivity is 2-3 times as large as the predicted value. Possibly soot containing hydrogen has a refractive index very different from pure carbon. Prediction of flame soot concentration can only be done at present on a semi-empirical basis for geometrically similar flames and with control variables close to the range studied. The controlled mixing history plug flow combustor is providing the laws relating the soot formation and combustion to the history of the fuel in the combustion chamber.

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