Environmental Engineering Reference
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Fig. 9 Spouted fluidized bed apparatus at TU-Darmstadt (left) and CFD model (right)
The simulation is carried out on a Dell workstation with quad-core Intel Xeon
CPU. Each run of 0- to 500-ms simulation time requires about 48 h of CPU time.
The simulation results for the particle distribution are presented in Fig. 10 alongside
the experimental observation for the
first 300 ms of the jet injection.
The simulation results of the average bed height and its comparison with the
experiment are presented in Fig. 11 a. The transient static pressure response at the
four monitoring locations of z = 2, 12, 22, and 40 cm is shown in Fig. 11 b.
As high-velocity gas enters the static bed from the central nozzle, it suddenly
experiences great resistance due to the presence of the particles. Due to the
momentum conservation, the static gas pressure near the central nozzle suddenly
builds up and is immediately felt by the lowest pressure transducer as shown in
Fig. 11 b. This pressure buildup can be explained by considering the solid pressure,
which is the additional pressure felt by a surface within the bed due to the presence
of the solid column above it. Because of both viscous friction and the pressure
gradient, part of the kinetic energy of the jet is transferred to the ambient particles,
forming a notable gas bubble originating from the central nozzle. The remaining
particles start to move upward making room for the growth of the gas bubble as
seen in Fig. 10 . The gas bubble keeps a steady growth rate for about 450 ms as can
be seen from Figs. 10 and 11 a during which the particles above the gas bubble get
accelerated, while the initial pressure buildup is gradually relieved. Around 450 ms,
the spouted bed height reaches its maximum value and the gas bubble begins to
collapse.
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