Abstract
Computational fluid dynamic (CFD) modeling of industrial
scale fluidized beds is a challenging task due to the
mismatch between a large process size and fine flow
structures. In the present work, methods are developed to
overcome the problems in order to make it possible to use
CFD as a costeffective tool for development of processes
based on the fluidized bed concept.
Two approaches to tackle the problems related to fine
flow structures are discussed: 1) transient simulation
using a coarse computational mesh and subgridscale
closure relations and 2) a steadystate simulation
approach that applies timeaveraged transport equations
for mass and momentum. The biggest benefit of the
transient coarsemesh simulation approach is that the
closure laws need to describe a much smaller fraction of
the total momentum transfer than what is the case in
steadystate modeling. The biggest drawback is that a
long simulation is required to produce the average flow
field. An additional complication is that the closure
laws have mesh resolution as a parameter. Steadystate
simulations produce the average flow field directly and
thus significantly reduce the computation time.
In this work, length scales of flow patterns in fluidized
beds are analyzed from experiments. Averaged transport
equations for mass and momentum are presented and the
terms in the equations are analyzed. It is shown that
drag force is one of the main terms to be modeled. A drag
correction coefficient is defined and ways to determine
it from transient CFD simulation data are presented. In
the work, correlations for both the spaceaveraged and
the timeaveraged drag forces are applied in riser
simulations.
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  20 May 2015 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9789513882464 
Electronic ISBNs  9789513882471 
Publication status  Published  2015 
MoE publication type  G5 Doctoral dissertation (article) 
Keywords
 CFD modeling
 fluidized bed
 gassolid drag
 cluster
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Cite this
Kallio, S. (2015). On modeling of the time or spaceaveraged gassolid drag force in fluidized bed conditions: Dissertation. VTT Technical Research Centre of Finland. http://www.vtt.fi/inf/pdf/science/2015/S86.pdf