Figure 1 . (a) The geometry of the fluidized bed and (b)
fluidization and visualization
systems.
2.2. Fluidization and visualization system
The fluidized bed and the corresponding high-speed visualization setup
are shown in Figure 1. The cylindrical fluidized bed contains an
optically-accessible acrylic column with an inner diameter of 63.5 mm
and a height of 930.0 mm (Figure 1a). The coordinate system used in the
paper has been indicated in Figure 1a, with the origin at the center of
the distributor plate’s upper surface, the x -axis pointing to the
right, and the z -axis pointing upward. Also shown in Figure 1a,
seven pressure differentials across two different axial locations (ΔP1-
ΔP7) have been measured at 100 Hz using high-frequency pressure
transducers with ranges of ±1866 Pa, ±1866 Pa, ±1866 Pa,
±1244 Pa, ±1244 Pa, ±1244 Pa,
0-7465 Pa, respectively. The top of the acrylic column is connected to a
HEPA filter, whereas the bottom is connected to a plenum chamber.
A distributor plate is placed
between the two flanges connecting the plenum and the acrylic column.
The plate is made out of sintered
metal and is rated at 40 media grade (Mott Corp). In a typical spouted
bed facility containing coarse particulate solids, fluid is often
injected vertically through a centrally located opening at the base of
the bed27. Note, such configuration has not been
implemented in the current setup.
The fluidization gas is supplied
into the plenum chamber from a centralized air compressor system at the
desired flow rate using an Alicat Scientific mass flow controller, with
a range of 0 - 500 SLPM and accuracies of ± (0.8% of reading + 0.2% of
full scale). Both the pressure transmitters and the flow controllers are
calibrated annually. Due to safety concerns, the absolute pressure of
the system is restricted by connecting the plenum chamber to a rupture
disk rated at 1.03 bar.
The experimental setup used to visualize the co-fluidization of the
mixture is shown in Figure 1b. The fluidized bed is backlit using a
rectangular white LED panel. For improving background inhomogeneity, a
diffuse paper was placed between the bed and the LED panel. The particle
motions are captured using a Phantom v641 CMOS camera equipped with a
Nikon® 50-mm lens operating at both 100 and 800 frames per second (fps).
The physical parameter space of the experiments has been summarized in
Table 2, with each case representing a different combination of bed
material. Case 1 provides the LDPE particles fluidization case as a
benchmark and Case 2 - 4 provides co-fluidization of LDPE particles and
wood pellets investigating the effects of static bed height, wood
particles fraction on the fluidization behavior of the binary mixing.
For each case, the effects of superficial gas velocity had also been
investigated. There is a slight variation on mean wood pellets weight,
but the variation is within 6% of the mean wood pellets mass. Also, the
wood pellets mass after the experiment has also been measured with a
negligible amount of mass loss due to attrition.
Table 2. Summary of parameter space.