4.3 Three-Dimensional Pebble Flow
203
Table 4.10 The parameter analysis for subdividing the gravity-driven dense pebble flow
Solid
concentration
Recirculation
flow rates (/s)
Intermittency
index C
RFKE
Pebble flow
regime
0.62–0.65
0.5
0.8592
0.993
Obviously
intermittent flow
1
0.7962
0.982
10
0.5027
0.880
50
0.2807
0.611
Transition
fluctuation flow
100
0.2017
0.439
300
0.1623
0.253
500
0.1188
0.0979
Consistent flow
1000
0.1048
0.0780
1250
0.0856
0.051
4.3 Three-Dimensional Pebble Flow
4.3.1 Voidage Distributions in HTR-10
This section analyzes the radial and axial distributions of the void fraction of a pebble
bed high-temperature reactor. A three-dimensional pebble bed corresponding to the
test facility of pebble-bed type gas-cooled high-temperature reactor (HTR-10) in
Tsinghua University is simulated via the softened discrete element method, and
the radial and axial void fraction profiles are calculated. It validates the oscillating
characteristics of the radial void fraction near the wall. Detailed calculations show
the differences of void fraction profiles between the stationary packing bed and the
dynamically discharging bed. Based on the vertically and circumferentially averaged
radial distribution and horizontally averaged axial distribution of the void fraction, a
fully three-dimensional analytical distribution of void fraction throughout the bed is
established. The results show the combined effects of gravity and void variation in
the pebble bed caused by the pebble discharging. It indicates the linearly increased
packing effect caused by gravity in the vertical (axial) direction and the normal
distribution of void in the horizontal (radial) direction by pebble drainage. These
two effects coexist in the conical base of the bed, whereas only the former effect
exists in the cylindrical volume of the bed.
In general, it is of fundamental significance to understand the flow and heat transfer characteristics throughout the pebble bed. The void fraction can influence the
pressure drop and heat transfer throughout the pebble bed and walls. Thus, the void
fraction/porosity in pebble-bed HTGRs has been the topic for many research projects.
203
Table 4.10 The parameter analysis for subdividing the gravity-driven dense pebble flow
Solid
concentration
Recirculation
flow rates (/s)
Intermittency
index C
RFKE
Pebble flow
regime
0.62–0.65
0.5
0.8592
0.993
Obviously
intermittent flow
1
0.7962
0.982
10
0.5027
0.880
50
0.2807
0.611
Transition
fluctuation flow
100
0.2017
0.439
300
0.1623
0.253
500
0.1188
0.0979
Consistent flow
1000
0.1048
0.0780
1250
0.0856
0.051
4.3 Three-Dimensional Pebble Flow
4.3.1 Voidage Distributions in HTR-10
This section analyzes the radial and axial distributions of the void fraction of a pebble
bed high-temperature reactor. A three-dimensional pebble bed corresponding to the
test facility of pebble-bed type gas-cooled high-temperature reactor (HTR-10) in
Tsinghua University is simulated via the softened discrete element method, and
the radial and axial void fraction profiles are calculated. It validates the oscillating
characteristics of the radial void fraction near the wall. Detailed calculations show
the differences of void fraction profiles between the stationary packing bed and the
dynamically discharging bed. Based on the vertically and circumferentially averaged
radial distribution and horizontally averaged axial distribution of the void fraction, a
fully three-dimensional analytical distribution of void fraction throughout the bed is
established. The results show the combined effects of gravity and void variation in
the pebble bed caused by the pebble discharging. It indicates the linearly increased
packing effect caused by gravity in the vertical (axial) direction and the normal
distribution of void in the horizontal (radial) direction by pebble drainage. These
two effects coexist in the conical base of the bed, whereas only the former effect
exists in the cylindrical volume of the bed.
In general, it is of fundamental significance to understand the flow and heat transfer characteristics throughout the pebble bed. The void fraction can influence the
pressure drop and heat transfer throughout the pebble bed and walls. Thus, the void
fraction/porosity in pebble-bed HTGRs has been the topic for many research projects.