Abstract
This thesis work concentrates on the area of dispersed
multiphase flows and, especially, to the problems
encountered while solving their governing equations
numerically with a collocated Control Volume Method
(CVM). To allow flexible description of geometry all
treatment is expressed in a form suitable for local Body
Fitted Coordinates (BFC) in a multiblock structure. All
work is related to conditions found in a simplified
fluidized bed reactor. The problems covered are the
treatment and efficiency of interphase coupling terms in
sequential solution, the exceeding of the bounds of
validity of the shared pressure concept in cases of high
dispersed phase pressure and the conservation of mass in
momentum interpolation for rapidly changing source terms.
The efficiency of different interphase coupling
algorithms is studied in typical fluidized bed
conditions, where the coupling of momentum equations is
moderate in most sections of the bed and where several
alternatives of different complexity exist. The
interphase coupling algorithms studied are the partially
implicit treatment, the Partial Elimination Algorithm
(PEA) and the SImultaneous solution of Nonlinearly
Coupled Equations (SINCE). In addition to these special
treatments of linearized coupling terms, the fundamental
ideas of the SINCE are applied also to the SIMPLE(C) type
pressure correction equation in the framework of the
Inter Phase Slip Algorithm (IPSA). The resulting
solution algorithm referred to as the InterPhase Slip
Algorithm  Coupled (IPSAC) then incorporates interface
couplings also into the mass balancing shared pressure
correction step of the solution.
It is shown that these advanced methods to treat
interphase coupling terms result in a faster convergence
of momentum equations despite of the increased number of
computational operations required by the algorithms. When
solving the entire equation set, however, this improved
solution efficiency is mostly lost due to the poorly
performing pressure correction step in which volume
fractions are assumed constant and the global mass
balancing is based on shared pressure. Improved pressure
correction algorithms utilizing separate fluid and
dispersed phase pressures, the Fluid Pressure in Source
term (FPS) and the Equivalent Approximation of Pressures
(EAP), are then introduced. Further, an expanded
RhieChow momentum interpolation scheme is derived which
allows equal treatment for all pressures. All the
computations are carried out in the context of a
collocated multiblock control volume solver CFDSFLOW3D.
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  1 Mar 2002 
Place of Publication  Espoo 
Publisher  
Print ISBNs  951385969X 
Electronic ISBNs  9513859703 
Publication status  Published  2002 
MoE publication type  G5 Doctoral dissertation (article) 
Keywords
 multiphase flow
 multifluid modelling
 interphase coupling
 phasic pressures
 numerical methods
 Control Volume Method
 Body Fitted Coordinates
 fluidized beds
 chemical reactors
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Karema, H. (2002). Numerical treatment of interphase coupling and phasic pressures in multifluid modelling: Dissertation. VTT Technical Research Centre of Finland. http://www.vtt.fi/inf/pdf/publications/2002/P458.pdf