Please cite this article in press as: Khodabandehlou, R., et al. Numerical investigation of gas bubble behavior in tapered fluidized beds. Particuology (2017), http://dx.doi.org/10.1016/j.partic.2017.05.013 ARTICLE IN PRESS G Model PARTIC-1048; No. of Pages 13 Particuology xxx (2017) xxx–xxx Contents lists available at ScienceDirect Particuology j our na l ho me page: www.elsevier.com/locate/partic Numerical investigation of gas bubble behavior in tapered fluidized beds Ramin Khodabandehlou, Hossein Askaripour, Asghar Molaei Dehkordi ∗ Department of Chemical and Petroleum Engineering, Sharif University of Technology, P.O. Box 11155-9465, Tehran, Iran a r t i c l e i n f o Article history: Received 9 April 2017 Received in revised form 25 May 2017 Accepted 25 May 2017 Available online xxx Keywords: Tapered fluidized beds Apex angle Particle size and density Bubble size distribution Rise velocity of bubbles a b s t r a c t In this article, the behavior of gas bubbles in tapered fluidized beds is investigated with the use of a two- fluid model incorporating kinetic theory of granular flow. The effects of various parameters such as apex angle, particle size, and particle density on the size distribution and the rise velocity of gas bubbles were examined. In addition, the simulation results for the bubble fraction and axial velocity of gas bubbles were compared with experimental data reported in the literature and good agreement was observed. As the apex angle was increased, the fraction of gas bubbles with large sizes increased and the fraction of bubbles with small sizes decreased. As the particle size increased, the fraction of gas bubbles with large diameters decreased; however, the fraction of bubbles with medium diameters increased. The obtained results clearly indicate that an increased solid density increased the bubble rise velocity up to a specified height and reduced the velocity at larger heights, in tapered fluidized beds. © 2017 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved. Introduction Fluidization is the phenomena of solid particles showing fluid- like behavior from the introduction of a fluid to the solid. Owing to the special characteristics created by contact between the solid and fluid phases, fluidized beds are appropriate for various industrial processes, such as biological treatment of wastewater, immobilized biofilm reactions, coal gasification, liquefaction, and catalytic poly- merization (Olazar, San Jose, Aguayo, Arandes, & Bilbao, 1992; Peng & Fan, 1997). Although most studies concerning fluidized beds have been conducted for columnar configurations, a new configuration, known as a tapered or conical fluidized bed, has been proposed in recent decades. In tapered fluidized beds, the fluid velocity at the bottom of the bed is high enough to ensure fluidization of large par- ticles. In addition, the decreasing fluid velocity in the axial direction prevents entrainment of small particles in the fluid phase. Because of their more stable pressure, conical fluidized beds can operate smoothly without any instabilities. This type of fluidized bed can be useful and beneficial for fluidization of solids with wide size and density distributions. Experimental examinations of the hydrodynamic behavior of tapered fluidized beds have been per- ∗ Corresponding author. Fax: +98 21 66022853. E-mail addresses: amolaeid@sharif.edu, amdehkordi@yahoo.com (A. Molaei Dehkordi). formed by Shi, Yu, and Fan (1984). The liquid and solid flow patterns and bed pressure drop for different superficial velocities of the fluid phase were studied. The hydrodynamic characteristics of tapered fluidized beds were experimentally determined, including the min- imum velocity of partial and full fluidization, and the maximum bed pressure drop. Important aspects of the dynamics of conical fluidized beds were explored by Biswal, Sahu, and Roy (1982). They conducted an exper- imental study of the fluctuation ratio for regular particles, and also determined correlations of the fluctuation ratio with particle diam- eter, bed diameter, static bed height, and the mass velocity of the fluid. A study on the hydrodynamic behavior of gas and solid phases was conducted by Lu, Zhao, Shen, Ding, and Jin (2006). They applied a two-dimensional two-fluid model (TFM) to simulate columnar and tapered risers. It was reported that the distribution of the solid volume fraction in the tapered risers was more uniform than that in columnar risers. Furthermore, the angle of the incline played a cru- cial role in the uniform distribution of the particles in the tapered risers. Markowski (1992) used a conical jet-spouted bed dryer with inert particles to dry animal blood plasma. The influence of oper- ating conditions on the final moisture content, product properties, and the throughput of the dryer were examined. It was found that the feed rate was the most important parameter affecting the effi- ciency and stability of the process. Passos, Massarani, Freire, and Mujumdar (1997) used a conical spouted bed with inert particles http://dx.doi.org/10.1016/j.partic.2017.05.013 1674-2001/© 2017 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.