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Kinetics and Structure of Superagglomerates Produced by Silane and AcetyleneThe evolution of smoke in a laminar diffusion flame involves several steps. The first step is particle inception/nucleation in the high-temperature fuel-rich region of the flame followed by surface growth and coagulation/coalescence of the small particles. As the primary spheres grow in size and lose hydrogen, the colliding particles no longer coalesce but retain their identity as a cluster of primary spheres, termed an agglomerate. Finally, in the upper portion of the flame, the particles enter an oxidizing environment which may lead to partial or complete burnout of the agglomerates. Currently there is no quantitative model for describing the growth of smoke agglomerates up to superagglomerates with an overall dimension of 10 microns and greater. Such particles are produced during the burning of acetylene and fuels containing benzene rings such as toluene and polystyrene. In the case of polystyrene, smoke agglomerates in excess of 1 mm have been observed "raining" out from large fires. Evidence of the formation of superagglomerates in a laminar acetylene/air diffusion flame has been recently reported. Acetylene was chosen as the fuel since the particulate loading in acetylene/air diffusion flames is very high. Photographs were obtained by Sorensen using a microsecond xenon lamp of the "stream" of soot just above the flame. For low flow rates of acetylene, only submicrometer soot clusters are produced and they give rise to the homogeneous appearance of the soot stream. When the flow rate is increased to 1.7 cu cm/s, soot clusters up to 10 microns are formed and they are responsible for the graininess and at a flow rate of 3.4 cu cm/s, a web of interconnected clusters as large as the width of the flame is seen. This interconnecting web of superagglomerates is described as a gel state by Sorensen et al (1998). This is the first observation of a gel for a gas phase system. It was observed that this gel state immediately breaks up into agglomerates due to buoyancy induced turbulence and gravitational sedimentation.
Document ID
19990054078
Acquisition Source
Glenn Research Center
Document Type
Conference Paper
Authors
Mulholland, G. W.
(National Inst. of Standards and Technology Gaithersburg, MD United States)
Hamins, A.
(National Inst. of Standards and Technology Gaithersburg, MD United States)
Sivathanu, Y.
(En'Urga, Inc. West Lafayette, IN United States)
Date Acquired
August 19, 2013
Publication Date
May 1, 1999
Publication Information
Publication: Fifth International Microgravity Combustion Workshop
Subject Category
Inorganic And Physical Chemistry
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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