Thermophoresis effect on volatile particle concentration in micro-organic dust flame

• Published in: Powder technology Vol. 217; pp. 69 - 76
• Main Authors: Bidabadi, Mehdi, Natanzi, Amir Hesam Ameri, Mostafavi, S. Alireza
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-02-2012; Elsevier
• Subjects: Accumulation; Applied sciences; Chemical engineering; Computational fluid dynamics; Dust; Exact sciences and technology; Fluid flow; Hydrodynamics; Hydrodynamics of contact apparatus; Mathematical models; Miscellaneous; Organic micro-particles; Particle volume fraction; Particle-laden flow; Reduction; Solid-solid systems; Thermophoretic; Vaporization; Volume fraction; Organic micro-particles; Particle volume fraction; Thermophoretic; Particle-laden flow; Accumulation; Vaporization; Correlation; Particle size; Gas mixture; Volume fraction; Buoyancy; Hydrodynamics; Modeling; Dust; Correlation analysis; Fuel; Mathematical model; Flame
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2011.10.010

In this paper, a mathematical model is proposed for the study of the structure of an upward-propagating flame that contains uniformly distributed volatile fuel particles in an oxidizing gas mixture. In order to obtain an appropriate model, the flame's front zone (the unburned zone) is divided into two zones: preheat and vaporization. In this research, physical phenomena such as thermophoretic effect, vaporization process and particle radius changes have been studied in the two mentioned zones. The vaporization process across the flame front leads to particle radius reduction, which can affect the particles' hydrodynamic behavior. As the thermophoretic force progressively increases by approaching the flame, it reaches a critical magnitude that just balances the gravity and buoyancy forces of the particles. At this point, the particle cloud remains stationary where the particles accumulate, and as a result, the volume fraction of particles reaches its maximum value. Particle size can strongly affect the hydrodynamic behavior of dust, and it can be stated that the increase of the radius of particles could lead to the reduction of the distance between the stagnation point (where the particle volume fraction is maximum) and the flame. The theoretical results show reasonable correlation with the experimental data.
Micro-organic particles are suspended in air and ignited by an electric spark near the bottom end of a vertical duct so that an upward flame is propagated in to the unburned mixture. The hydrodynamic behavior of two phase flow including air and solid particles has been investigated to estimate particle concentration and its velocity profile. [Display omitted]
► Thermophoresis phenomenon is dominant in the reactive particle hydrodynamics. ► For the smaller particle flame temperature and burning velocity is more. ► Thermophoresis effect decreases with the particle size. ► Particle accumulation takes place in stagnation point. ► For larger particle stagnation point is closer to the flame front.