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Mechanical Engineering Department, Dalhousie University, B3J 1B6, Halifax, Canada.
Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
Mechanical and Aerospace Eng. Dept., Carleton University Ottawa, Ontario, K1S 5B6, Canada.
2006 (English)In: International Heat Transfer Conference, IHTC-13, 2006Conference paper (Refereed)
Abstract [en]

In this study, we present an empirical model for bed-to-surface heat transfer in Circulating Fluidized Beds (CFB) with secondary air (SA) injection. The model is based on a correlation that relates the heat transfer coefficient to cross-sectionally averaged solids holdup. The average solids holdup was correlated with the operating and design parameters of CFBs with SA injection using three dimensionless parameters: Archimedes number, Gs/rp(U0-USA) and (1-HSA/Hr). The correlations were obtained using least square analysis for a wide range of data available in the literature as well as the data obtained in this study for two types of SA injectors: radial and tangential. The data used in developing the correlations cover a range of 2.0 to 8.6 m/s for superficial gas velocity, 5 to 100 kg/m2s for solids circulation rate, 0-0.6 for secondary to primary air ratio, and 60 to 300 mm for particle diameter (Groups A and B). The predictions obtained with the correlations show good agreement with the experimental data. Furthermore, an experimental correlation, developed in our previous work for prediction of wall-to-bed heat transfer coefficient in CFB risers operated with SA was used in a parametric study to investigate the effects of design and operating parameters on heat transfer. The results of the parametric study indicate that the heat transfer coefficient increases with increasing secondary air ratio, solids circulation rate, and height of secondary air injection port. The tangential SA injector was found to result in a significant increase in heat transfer coefficient compared with radial injector and non-SA operation due to increase in average solids holdup. This is consistent with the available data in the literature.

Place, publisher, year, edition, pages
Keyword [en]
Heat Transfer, Circulating Fluidized Beds, Secondary Air Injection
URN: urn:nbn:se:umu:diva-20068DOI: 10.1615/IHTC13.p12ISBN: 1-56700-225-0OAI: diva2:208056
Available from: 2009-03-16 Created: 2009-03-16 Last updated: 2009-03-16Bibliographically approved

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