Pressure effects on the spectral behavior of the thermal field in non-reacting and low Damköhler reacting flows

• Published in: International journal of thermal sciences 1999, Vol.38 (9), p.819-831
• Main Authors: Bounif, Abdelhamid, Aris, Abdelkader, Gökalp, Iskender
• Format: Article
• Language: English
• Subjects: Applied sciences; champ thermique; Combustion of gaseous fuels; Combustion. Flame; effets de la pression; Energy; Energy. Thermal use of fuels; Exact sciences and technology; faible nombre de Damköhler; fil froid; jet-stirred reactor; jets; low Damköhler number; modélisation; mécanismes réactionnels; pressure effects; reaction mechanism; réacteur auto-agité; temperature field; Theoretical studies. Data and constants. Metering; thermoanemometry; turbulence; turbulence modeling
• ISSN: 1290-0729; 1778-4166
• DOI: 10.1016/S1290-0729(99)80037-4

This study concerns the regime of distributed reaction zones of a well-stirred reactor. No mention has been made until now on the fields of the interaction between combustion and turbulence in this regime, where the Damköhler number is below unity. The aim of this paper is to investigate the fluctuating temperature structures inside the well stirred-reactor for various mean pressure situations. The experimental study is conducted by the technique of fine-wire thermoanemometry. In parallel, the fuel conversion rates of propane oxidation in all the experimental conditions are determined from a simulation work which takes into account a detailed kinetic model. The different relevant characteristics of the dynamic field are estimated by means of the k- ε model. The variation of the unmixedness and the time scales of the temperature field is compared for various pressures in the reacting and non-reacting cases. The discussion is conducted in terms of the ratio between the time scales of the scalar and dynamic fields. The main conclusions are as follows. When the reacting and non-reacting temperature fields are compared at the same mean pressure, the effect of the chemical reactions appears to be the feeding of more energy into the small scale turbulence structures. It is important to notice that the systematic decrease of time and length scales with the mean pressure in the reactor, together with a very significant increase of the dissipation rate of the temperature fluctuations, gives evidence for a positive effect of the increase of the pressure on the micromixing. Le présent travail porte sur l'investigation du champ thermique instantané dans un réacteur auto-agité par jets gazeux. Afin d'aborder à la fois le problème du micro-mélange réalisé au sein du réacteur et celui de l'interaction combustion-turbulence à faible nombre de Damköhler, cette analyse permet de vérifier les prévisions sur les effets de compressibilité dus à la variation de la pression avec et sans réactions chimiques dans la zone des réactions distribuées. La technique expérimentale est la thermoanémométrie à fil froid. Les principales caractéristiques du champ dynamique sont estimées à partir des équations de conservation décrites par le modèle de la turbulence ( k, ε). Les effets couplés de la compressibilité et de la diffusion thermique tendent à rendre les petites structures plus énergétiques et les nombres de Reynolds moyen et turbulent plus importants. Ainsi, pour des pressions croiss