Modeling of multiphase flows in a spray dryer
Ladda ner
Typ
Examensarbete för masterexamen
Program
Innovative and sustainable chemical engineering (MPISC), MSc
Publicerad
2021
Författare
Vasudevan, Sindhuja
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Spray drying is a robust and popular unit operation in the pharmaceutical industry.
One of the many applications of this unit operation is the manufacture of dry dosage
formulations for nasal or pulmonary delivery. It is important that the generated
particles from the spray drying process have certain attributes such as flowability,
dispersibility and suitable aerodynamic properties, which depend on the particle
design. In order to obtain a suitable particle design, a sound understanding of the
particle formation process, which includes the physical and chemical mechanisms
that control the drying process, is required. In this thesis, the drying process is
studied by modeling with the commercial computational fluid dynamics (CFD) code
ANSYS Fluent. This multiphase system which includes a gaseous continuous phase
and droplet/particle as the dispersed phase is modeled using an Euler-Lagrangian
approach. In Euler-Lagrangian modeling, the fluid phase is modeled as a continuum
while for the dispersed phase a large number of individual particles is modeled. The
different phases are said to be coupled when there is exchange of momentum, mass
and energy between them. The significant presence of exchange of mass and heat
between the continuous and dispersed phase indicates that the phases are two-way
coupled, i.e., the continuous phase transfers mass and heat to dispersed phase and
vice-versa. The effect of turbulence on the dispersed phase is accounted through a
turbulent dispersion model. The choice of characteristic parameter of the turbulent
dispersion model, i.e., the ’number of tries’ is decided based on a sensitivity analysis.
This is done by analysing its effect on the residence time distribution of the dispersed
phase. Analysis of the drying data obtained from the simulation reveals that the rate
of drying of droplets of same initial diameter is different since they follow different
trajectories. That is, for droplets of the same initial diameter, the drying rate varies
in such a way that the maximum value is around 50% higher than the minimum
value. Hence, this implies corresponding variation in solute concentration profile in
the droplet and hence, particle structure for particles obtained from droplets of same
initial diameter. Additionally, the impact of process operating conditions, especially
the mass flow rate of the solution, on the drying rate and hence, the corresponding
particle structure is indicated.
Beskrivning
Ämne/nyckelord
Spray Drying , Euler-Lagrangian , Discrete Phase Model , Drying Rate