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Heat transfer augmentation / Andreas Hantsch in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023505-1/6] Titre : Heat transfer augmentation : radiative-convective heat transfer in a tube with fiber array inserts Type de document : texte imprimé Auteurs : Andreas Hantsch, Auteur ; Ulrich Gross, Auteur ; Andrew R. Martin, Auteur Article en page(s) : pp. [023505-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Convection  Porosity  Silicon  compounds  Stainless  steel  Turbulence Index. décimale : 536 Chaleur. Thermodynamique Résumé : Gas-phase heat transfer plays a critical role in many high temperature applications, such as preheaters, combustors, and other thermal equipment. In such cases common heat transfer augmentation methods rely on the convective component alone to achieve improved internal performance. Radiatively assisted heat transfer augmentation has been suggested as a way to overcome limitations in convective-only enhancement. One example of such a technique is the fiber array insert; thermal radiation emitted by tube walls is captured by a large number of slender fibers, which in turn convect heat to the flowing fluid. Previous numerical studies have indicated that this technique represents a promising enhancement method warranting further investigation. This paper presents results from an experimentally based feasibility study of fiber array inserts for heat transfer augmentation in an externally heated duct. Fibers composed of 140 µm silicon carbide and 150 µm stainless steel were assembled in arrays with porosities around 0.98, and were tested for empty-tube Reynolds numbers ranging from 17,500 to 112,500 and wall temperatures from ambient up to 750°C. The arrays cause a significant pressure drop—roughly two orders of magnitude higher than the empty-tube case—but tube-side heat transfer coefficients were improved by up to 100% over the convective-only case in the low flow rate regime. The stainless steel fiber array exhibited similar heat transfer performance as the silicon carbide case, although pressure drop characteristics differed owing to variations in fluid-structure flow phenomena. Pressure drop data were roughly within the range of d'Arcy law predictions for both arrays, and deviations could be explained by inhomogeneities in fiber-to-fiber spacing. Heat transfer was found to depend nonlinearly on wall temperature and flow rate, in contrast to previously reported numerical data. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heat transfer augmentation : radiative-convective heat transfer in a tube with fiber array inserts [texte imprimé] / Andreas Hantsch, Auteur ; Ulrich Gross, Auteur ; Andrew R. Martin, Auteur . - pp. [023505-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023505-1/6] Mots-clés : Convection  Porosity  Silicon  compounds  Stainless  steel  Turbulence Index. décimale : 536 Chaleur. Thermodynamique Résumé : Gas-phase heat transfer plays a critical role in many high temperature applications, such as preheaters, combustors, and other thermal equipment. In such cases common heat transfer augmentation methods rely on the convective component alone to achieve improved internal performance. Radiatively assisted heat transfer augmentation has been suggested as a way to overcome limitations in convective-only enhancement. One example of such a technique is the fiber array insert; thermal radiation emitted by tube walls is captured by a large number of slender fibers, which in turn convect heat to the flowing fluid. Previous numerical studies have indicated that this technique represents a promising enhancement method warranting further investigation. This paper presents results from an experimentally based feasibility study of fiber array inserts for heat transfer augmentation in an externally heated duct. Fibers composed of 140 µm silicon carbide and 150 µm stainless steel were assembled in arrays with porosities around 0.98, and were tested for empty-tube Reynolds numbers ranging from 17,500 to 112,500 and wall temperatures from ambient up to 750°C. The arrays cause a significant pressure drop—roughly two orders of magnitude higher than the empty-tube case—but tube-side heat transfer coefficients were improved by up to 100% over the convective-only case in the low flow rate regime. The stainless steel fiber array exhibited similar heat transfer performance as the silicon carbide case, although pressure drop characteristics differed owing to variations in fluid-structure flow phenomena. Pressure drop data were roughly within the range of d'Arcy law predictions for both arrays, and deviations could be explained by inhomogeneities in fiber-to-fiber spacing. Heat transfer was found to depend nonlinearly on wall temperature and flow rate, in contrast to previously reported numerical data. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]