Flow behavior and regime transition in a high-density circulating fluidized bed riser

Kim, SW
Külah, Görkem
Bi, H
Lim, CJ
Grace, JR
Flow behavior and flow regime transitions were determined in a circulating fluidized bed riser (0.203 m i.d. x 5.9 m high) of FCC particles (d(p) = 70 pm, rho(p) = 1700 kg/m(3)). A momentum probe was used to measure radial profiles of solids momentum flux at several heights and to distinguish between local net upward and downward flow. In the experimental range covered (U-g = 5-8 m/s; G(s) = 22-345 kg/m(2) s), the fast fluidization flow regime was observed to coexist with dense suspension upflow (DSU). At a constant gas velocity, net downflow of solids near the wall disappeared towards the bottom of the riser with increasing solids mass flux, with dense suspension upflow achieved where there was no refluxing of solids near the riser wall on a time-average basis. The transition to DSU conditions could be distinguished by means of variations of net solids flow direction at the wall, annulus thickness approaching zero and flattening of the solids holdup versus G(s) trend. A new flow regime map is proposed distinguishing the fast fluidization, DSU and dilute pneumatic transport flow regimes.


Flow structure and thickness of annular downflow layer in a circulating fluidized bed riser
Kim, SW; Külah, Görkem; Bi, HT; Lim, CJ; Grace, JR (2004-04-08)
Flow structures were determined in a circulating fluidized bed (CFB) riser (0.203 m i.d. x 5.9 m high) of FCC particles (d(p)=70 mum, rho(s)= 1700 kg/m(3)). A momentum probe was used to measure radial momentum flux profiles at several levels and to distinguish between upward and downward flow regions. Time-mean dynamic pressure (DeltaP(m)) decreases towards the wall in the range U-g=5-8 m/s, G(s)=10-340 kg/m(2) s. The thickness of the annular downflow layer based on DeltaP(m)=0 reaches a maximum with increa...
Flow structure characterization in conical spouted beds using pressure fluctuation signals
MOSTOUFI, Navid; Külah, Görkem; KÖKSAL, MURAT (2015-01-01)
Characteristics of the hydrodynamics of conical spouted beds were revealed by analyzing pressure fluctuation signals in the frequency domain. Experiments were carried out in spouted beds with three different cone angles (30 degrees, 45 degrees, 60 degrees) and high density spherical particles (rho(p) = 6050 kg/m(3)) with diameters of 0.5 or 1 mm. Different hydrodynamic structures in the movement of solids were identified by examining pressure fluctuations of the bed in the frequency domain. Peaks in the pow...
Flow Characterization of Viscoelastic Fluids around Square Obstacle
Tezel, Guler Bengusu; YAPICI, Kerim; Uludağ, Yusuf (Periodica Polytechnica Budapest University of Technology and Economics, 2019-01-01)
This study focuses on the computational implementation of structured non-uniform finite volume method for the 2-D laminar flow of viscoelastic fluid past a square section of cylinder in a confined channel with a blockage ratio 1/4 for Re = 10(-)(4), 5, 10 and 20. Oldroyd-B model (constant viscosity with elasticity) and the PTT model (shear-thinning with elasticity) are the constitutive models considered. In this study effects of the elasticity and inertia on the drag coefficients and stress fields around th...
Streamwise oscillations of a cylinder beneath a free surface: Free surface effects on fluid forces
Kocabiyik, Serpil; Bozkaya, Canan (2015-11-01)
A two-dimensional free surface flow past a circular cylinder forced to perform streamwise oscillations in the presence of an oncoming uniform flow is investigated at a Reynolds number of R=200 and fixed displacement amplitude, A=0.13, for the forcing frequency-to-natural shedding frequency ratios, f/f(0) = 1.5, 2.5, 3.5. The present two-fluid model is based on a velocity-pressure formulation of the two-dimensional continuity and unsteady Navier-Stokes equations. The continuity and Navier-Stokes equations ar...
Bubble size control in a two-dimensional fluidized bed using a moving double plate distributor
Koksal, M; Vural, H (1998-03-01)
Pulsating the flow in a fluidized bed by using a moving double plate distributor (MDPD) lo control the bubble size and enhance the fluidization characteristics is a new approach. In this novel design, a second plate Is placed under the existing distributor such that it can make a reciprocating motion generating pulses to the flow field. The frequency and amplitude of the pulsation can be adjusted to break up the large bubbles in the bed. The aim of this study is to investigate the effect of pulsation on the...
Citation Formats
S. Kim, G. Külah, H. Bi, C. Lim, and J. Grace, “Flow behavior and regime transition in a high-density circulating fluidized bed riser,” CHEMICAL ENGINEERING SCIENCE, pp. 3955–3963, 2004, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/47937.