Chapter 2
Experiments in Pebble Flows
2.1 Experimental Test Facility
The schematic diagram of the experimental setup is depicted in Fig. 2.1. The experimental facility is fabricated based on the design of a practical reactor core, and a
three-dimensional cylinder structure is modeled by a two-dimensional 1/5 scaled
model. The experimental vessel is a sliced model equivalent to an axial central cut
piece of the three-dimensional cylinder model scaled with the same ratio. The geometries of the vessel, including the base angle (measured from the horizontal plane) and
the discharge hole diameter, are supposed to have great effects on pebble flow. The
base angles of 30, 45 and 60
◦ , and different surface roughness of pebbles are considered. Experimental vessels for various combinations of bed and pebble parameters
are set up to determine the parameter influences on the characteristics of pebble
flow. The experiments and conclusions discussed in this chapter are valid for one
combination of these parameters.
Due to the limited two-dimensional model, the pebble flow of the experimental
pebble bed may not be exactly simulated as the actual flow in a practical reactor core,
and conclusions obtained in this chapter may not be directly applicable to a practical
reactor design. However, essential geometries and pebble parameters, including base
angle, the diameter of a discharge hole, and the size of pebbles, etc., are determined
based on the practical reactor core design so that the obtained studies still have a
valuable practical meaning of the preliminary design guideline. On the other hand,
these studies are focused on the essential characteristics of pebble flow and it could
be considered that the results revealed the generic characteristics of the pebble flow
in a reactor core.
The main body of the experimental setup is a vessel enclosed by six plexiglass
plane walls that are transparent for easy visual inspection. To avoid the crystallization
of pebbles along the plane walls, all internal flow surfaces of the walls are slotted
with dish-like indentations to enhance random motions of the pebbles. The vessel is
about 1,000 mm in total height with an upright rectangular prism with a width of 800
mm and a height of 804 mm. A cone forms the base of the vessel, and the base angle
© Tsinghua University Press 2021
S. Jiang et al., Multiphase Flow and Heat Transfer in Pebble Bed Reactor Core,
https://doi.org/10.1007/978-981-15-9565-3_2
43
Experiments in Pebble Flows
2.1 Experimental Test Facility
The schematic diagram of the experimental setup is depicted in Fig. 2.1. The experimental facility is fabricated based on the design of a practical reactor core, and a
three-dimensional cylinder structure is modeled by a two-dimensional 1/5 scaled
model. The experimental vessel is a sliced model equivalent to an axial central cut
piece of the three-dimensional cylinder model scaled with the same ratio. The geometries of the vessel, including the base angle (measured from the horizontal plane) and
the discharge hole diameter, are supposed to have great effects on pebble flow. The
base angles of 30, 45 and 60
◦ , and different surface roughness of pebbles are considered. Experimental vessels for various combinations of bed and pebble parameters
are set up to determine the parameter influences on the characteristics of pebble
flow. The experiments and conclusions discussed in this chapter are valid for one
combination of these parameters.
Due to the limited two-dimensional model, the pebble flow of the experimental
pebble bed may not be exactly simulated as the actual flow in a practical reactor core,
and conclusions obtained in this chapter may not be directly applicable to a practical
reactor design. However, essential geometries and pebble parameters, including base
angle, the diameter of a discharge hole, and the size of pebbles, etc., are determined
based on the practical reactor core design so that the obtained studies still have a
valuable practical meaning of the preliminary design guideline. On the other hand,
these studies are focused on the essential characteristics of pebble flow and it could
be considered that the results revealed the generic characteristics of the pebble flow
in a reactor core.
The main body of the experimental setup is a vessel enclosed by six plexiglass
plane walls that are transparent for easy visual inspection. To avoid the crystallization
of pebbles along the plane walls, all internal flow surfaces of the walls are slotted
with dish-like indentations to enhance random motions of the pebbles. The vessel is
about 1,000 mm in total height with an upright rectangular prism with a width of 800
mm and a height of 804 mm. A cone forms the base of the vessel, and the base angle
© Tsinghua University Press 2021
S. Jiang et al., Multiphase Flow and Heat Transfer in Pebble Bed Reactor Core,
https://doi.org/10.1007/978-981-15-9565-3_2
43