Abstract
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) 
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Keywords
 CFD modeling
 fluidized bed
 gassolid drag
 cluster
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On modeling of the time or spaceaveraged gassolid drag force in fluidized bed conditions : Dissertation. / Kallio, Sirpa.
Espoo : VTT Technical Research Centre of Finland, 2015. 175 p.Research output: Thesis › Dissertation › Collection of Articles
TY  THES
T1  On modeling of the time or spaceaveraged gassolid drag force in fluidized bed conditions
T2  Dissertation
AU  Kallio, Sirpa
PY  2015
Y1  2015
N2  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.
AB  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.
KW  CFD modeling
KW  fluidized bed
KW  gassolid drag
KW  cluster
M3  Dissertation
SN  9789513882464
T3  VTT Science
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 