4.2 Gravity-Driven Flow Regime Characterization
189
the DPF has been discussed based on the analysis of combined parameters, i.e., the
intermittency index C and relative fluctuating kinetic energy (RFKE).
Most studies focused on the granular flow in the silo bed where the drainage
of pebble flows freely. On the contrary, few researchers ever paid attention to the
operation method that the recirculation flow rate is set constant. This special operation
method is applied in the high-temperature gas-cooled nuclear reactor (HTGR), which
is considered as one potential solution for the generation-IV advanced reactor [44].
The effects of various flow rates on the flow regimes are vital to the efficiency and
safety of HTGR. Pebbles’ behavior should be insured to fulfill thermal-hydraulic
rules and radiation safety requirements [45].
4.2.4.1 Simulation Conditions
The geometry of the numerical setup (Fig. 4.16), is based on the pebble-bed experiment vessel [46]. Notably, the material properties of lateral walls also come from
the same experimental test facility whose walls are made of plexiglass. Simulated
plexiglass pebbles are identical spheres with a diameter of 12 mm. Simulated pebble
bed is 800 × 1200 × 28 mm in width, height and depth, respectively (Fig. 4.16), and
its width and height follow a 1:5 scale of a real pebble-bed reactor, named HTR-10.
This computational domain is a middle layer of the 3D bed. This layer-like domain
is a middle longitudinal section of the bed with a little larger than two pebble diameters. Simulation parameters like friction coefficient and Poisson rate are determined
based on material test of plexiglass. The simulation parameters are listed in Table 4.6
[47]. As indicated by Ref. [48], though the modulus of soft material (70 MPa) in
simulation is only
1
1000
of the hard material (7000 MPa), they found no significant
Fig. 4.16 Sketc.h of
simulation setup
189
the DPF has been discussed based on the analysis of combined parameters, i.e., the
intermittency index C and relative fluctuating kinetic energy (RFKE).
Most studies focused on the granular flow in the silo bed where the drainage
of pebble flows freely. On the contrary, few researchers ever paid attention to the
operation method that the recirculation flow rate is set constant. This special operation
method is applied in the high-temperature gas-cooled nuclear reactor (HTGR), which
is considered as one potential solution for the generation-IV advanced reactor [44].
The effects of various flow rates on the flow regimes are vital to the efficiency and
safety of HTGR. Pebbles’ behavior should be insured to fulfill thermal-hydraulic
rules and radiation safety requirements [45].
4.2.4.1 Simulation Conditions
The geometry of the numerical setup (Fig. 4.16), is based on the pebble-bed experiment vessel [46]. Notably, the material properties of lateral walls also come from
the same experimental test facility whose walls are made of plexiglass. Simulated
plexiglass pebbles are identical spheres with a diameter of 12 mm. Simulated pebble
bed is 800 × 1200 × 28 mm in width, height and depth, respectively (Fig. 4.16), and
its width and height follow a 1:5 scale of a real pebble-bed reactor, named HTR-10.
This computational domain is a middle layer of the 3D bed. This layer-like domain
is a middle longitudinal section of the bed with a little larger than two pebble diameters. Simulation parameters like friction coefficient and Poisson rate are determined
based on material test of plexiglass. The simulation parameters are listed in Table 4.6
[47]. As indicated by Ref. [48], though the modulus of soft material (70 MPa) in
simulation is only
1
1000
of the hard material (7000 MPa), they found no significant
Fig. 4.16 Sketc.h of
simulation setup