2.5 Particle Velocimetry Measurements
83
tion is increased. Meanwhile, particles remain less correlated with their previous
velocities when they flow along the streamlines toward the outlet.
• Pattern 3: With larger intermittency and lower velocity in the near-wall region
and the stagnant zone. In light of the compact packing and compression, particles
move singly with longer intervals over stationary and bulk motion events instead
of flowing in clusters. Moreover, the higher concentration of packing may cause
less velocity autocorrelation in the lower places of the stagnant zone.
2.5.3.9 Pebble Flow Fields
The flow field characteristics are of fundamental importance in the design work
of the pebble-bed high-temperature gas-cooled reactor. The different effects of bed
configurations on the flow characteristics of a pebble bed are studied through the
PTV experiment. Some criteria, e.g., flow uniformity (σ ) and mass flow level (α), are
proposed to estimate the vertical velocity field and compare the bed configurations.
The distribution of the δθ (angle difference between the individual particle velocity
and the velocity vector sum of all particles) is also used to estimate the resultant
motion consistency level. Moreover, for each bed configuration, the thickness of
displacement is analyzed to measure the effect of the funnel flow zone based on the
boundary layer theory. Detailed information shows the quantified characteristics of
bed configuration effects on flow uniformity and other characteristics. The sequence
of levels of each estimation criterion is obtained for all bed configurations. In addition,
a good design of the pebble-bed configuration is suggested and these estimation
criteria can also be applied and adopted in testing other geometry designs of the
pebble bed.
2.5.3.10 Experimental Setup
In this study, a 2-D test facility is designed based on a real pebble-bed reactor at
Tsinghua University with a scale of 1:5 (Fig.2.25a). The experimental setup consists
of several main parts. Firstly, the vessel is made up of plexiglass, which has dimensions of 800×1000×120mm in width, height, and thickness, respectively. About
70000 black glass pebbles with a diameter of 12mm are filled [1]. Secondly, three
inlet tubes are set on the vessel top through which the pebbles can fall into the bed.
Finally, the discharge hole is located at the bottom of the setup, with 120mm in
diameter and 200mm in length.
The operation method is described as follows [40, 41]: 1). The experiment begins
with the random packing by pre-filling the black pebbles in the vessel. 2). The pebble
bed is fed with 14, 122, and 14 pebbles per minute from the left, center, and right
inlet tubes, respectively. The pebbles from the central inlet tube represent the graphite
moderator pebbles, while the ones from the two side inlet tubes stand for the fuel
pebbles in the real pebble-bed reactor. 3). Meanwhile, pebbles are discharged from
the outlet hole at a rate of 150 pebbles per minute. Thus, the total number of pebbles
83
tion is increased. Meanwhile, particles remain less correlated with their previous
velocities when they flow along the streamlines toward the outlet.
• Pattern 3: With larger intermittency and lower velocity in the near-wall region
and the stagnant zone. In light of the compact packing and compression, particles
move singly with longer intervals over stationary and bulk motion events instead
of flowing in clusters. Moreover, the higher concentration of packing may cause
less velocity autocorrelation in the lower places of the stagnant zone.
2.5.3.9 Pebble Flow Fields
The flow field characteristics are of fundamental importance in the design work
of the pebble-bed high-temperature gas-cooled reactor. The different effects of bed
configurations on the flow characteristics of a pebble bed are studied through the
PTV experiment. Some criteria, e.g., flow uniformity (σ ) and mass flow level (α), are
proposed to estimate the vertical velocity field and compare the bed configurations.
The distribution of the δθ (angle difference between the individual particle velocity
and the velocity vector sum of all particles) is also used to estimate the resultant
motion consistency level. Moreover, for each bed configuration, the thickness of
displacement is analyzed to measure the effect of the funnel flow zone based on the
boundary layer theory. Detailed information shows the quantified characteristics of
bed configuration effects on flow uniformity and other characteristics. The sequence
of levels of each estimation criterion is obtained for all bed configurations. In addition,
a good design of the pebble-bed configuration is suggested and these estimation
criteria can also be applied and adopted in testing other geometry designs of the
pebble bed.
2.5.3.10 Experimental Setup
In this study, a 2-D test facility is designed based on a real pebble-bed reactor at
Tsinghua University with a scale of 1:5 (Fig.2.25a). The experimental setup consists
of several main parts. Firstly, the vessel is made up of plexiglass, which has dimensions of 800×1000×120mm in width, height, and thickness, respectively. About
70000 black glass pebbles with a diameter of 12mm are filled [1]. Secondly, three
inlet tubes are set on the vessel top through which the pebbles can fall into the bed.
Finally, the discharge hole is located at the bottom of the setup, with 120mm in
diameter and 200mm in length.
The operation method is described as follows [40, 41]: 1). The experiment begins
with the random packing by pre-filling the black pebbles in the vessel. 2). The pebble
bed is fed with 14, 122, and 14 pebbles per minute from the left, center, and right
inlet tubes, respectively. The pebbles from the central inlet tube represent the graphite
moderator pebbles, while the ones from the two side inlet tubes stand for the fuel
pebbles in the real pebble-bed reactor. 3). Meanwhile, pebbles are discharged from
the outlet hole at a rate of 150 pebbles per minute. Thus, the total number of pebbles