3 Dynamics of Spray Granulation in Continuously …
73
˙
n
−
in,i, j = ˙
n
+
out,i−1, j ,
(10)
˙
n
+
in,i, j = n
−
out,i+1, j .
(11)
Particle flows that enter from or leave to a previous chamber are denoted by “−”.
Those that enter from or leave to a subsequent chamber are denoted by “+” (see
Fig. 2). In case of the first and the last chamber these equations have to be modified,
since there is no previous or subsequent chamber, respectively. For the first chamber
the inlet flows ˙
n
−
in,1, j and the outlet flows ˙
n
−
out,1, j are 0. The same applies for the inlet
flows ˙
n
+
in,I, j of the last chamber. The product flow is the sum of forward outlet flows
of the last chamber ˙
n
+
out,I, j .
The particle flow at the chamber inlet and outlet depends on various factors, for
example particle properties, like particle size and density distribution, the fluidization
regime as well as the geometric design of the weir. Weirs, therefore, may have
influence on the overall movement and recirculation of particles and mixtures in
a process chamber. The characterization of the weir influence can be performed
experimentally by particle tracking velocimetry (PTV) as described by Meyer et al.
[17] or theoretically by combination of computational fluid dynamics (CFD) and
discrete element method (DEM).
3 Determination of Inter-chamber Particle Transfer
In solids processing in horizontal fluidized beds the formation of residence time distributions and subsequently of property distributions, for instance in moisture content,
particle size or chemical composition, are observed. Residence time distributions
are due to partial recirculation of particles against the main transport direction. It
is known that the installation of weirs, thus dividing the apparatus into multiple
chambers, influences the overall residence time distribution.
Weirs are rectangular plates which are installed perpendicular to the main solid
transport direction. Three common designs exist, shown in Fig. 3: Over-flow weirs
which are installed directly on top of the distributor plate so that particles have to
overcome the weir; under-flow weirs with a defined gap between weir and distributor
plate; and side-flow weirs which are similar to under-flow weirs, however, the gap
only exists over a certain portion of the apparatus width.
The effect of individual weirs on the observed dispersion has not been fully understood with respect to operation parameters, material properties or weir geometry.
Therefore, methods were developed and tested that allow investigating the particle
transfer from one chamber to another and vice versa. In contrast to previous attempts
to characterize the transport behavior by tracer experiments (see for instance [18–
21]), particle tracking velocimetry (PTV) was utilized. The main advantage is that
PTV allows the determination of exchange rates on single particle basis.
73
˙
n
−
in,i, j = ˙
n
+
out,i−1, j ,
(10)
˙
n
+
in,i, j = n
−
out,i+1, j .
(11)
Particle flows that enter from or leave to a previous chamber are denoted by “−”.
Those that enter from or leave to a subsequent chamber are denoted by “+” (see
Fig. 2). In case of the first and the last chamber these equations have to be modified,
since there is no previous or subsequent chamber, respectively. For the first chamber
the inlet flows ˙
n
−
in,1, j and the outlet flows ˙
n
−
out,1, j are 0. The same applies for the inlet
flows ˙
n
+
in,I, j of the last chamber. The product flow is the sum of forward outlet flows
of the last chamber ˙
n
+
out,I, j .
The particle flow at the chamber inlet and outlet depends on various factors, for
example particle properties, like particle size and density distribution, the fluidization
regime as well as the geometric design of the weir. Weirs, therefore, may have
influence on the overall movement and recirculation of particles and mixtures in
a process chamber. The characterization of the weir influence can be performed
experimentally by particle tracking velocimetry (PTV) as described by Meyer et al.
[17] or theoretically by combination of computational fluid dynamics (CFD) and
discrete element method (DEM).
3 Determination of Inter-chamber Particle Transfer
In solids processing in horizontal fluidized beds the formation of residence time distributions and subsequently of property distributions, for instance in moisture content,
particle size or chemical composition, are observed. Residence time distributions
are due to partial recirculation of particles against the main transport direction. It
is known that the installation of weirs, thus dividing the apparatus into multiple
chambers, influences the overall residence time distribution.
Weirs are rectangular plates which are installed perpendicular to the main solid
transport direction. Three common designs exist, shown in Fig. 3: Over-flow weirs
which are installed directly on top of the distributor plate so that particles have to
overcome the weir; under-flow weirs with a defined gap between weir and distributor
plate; and side-flow weirs which are similar to under-flow weirs, however, the gap
only exists over a certain portion of the apparatus width.
The effect of individual weirs on the observed dispersion has not been fully understood with respect to operation parameters, material properties or weir geometry.
Therefore, methods were developed and tested that allow investigating the particle
transfer from one chamber to another and vice versa. In contrast to previous attempts
to characterize the transport behavior by tracer experiments (see for instance [18–
21]), particle tracking velocimetry (PTV) was utilized. The main advantage is that
PTV allows the determination of exchange rates on single particle basis.