70
2 Experiments in Pebble Flows
2.5.3.1 Experimental Procedures and Methods
The experimental apparatus [17] is designed based on a real pebble-bed reactor at the
scale 1:5 (Fig. 2.15a). It runs in the way of the recirculation mode, i.e., the pebbles
discharged from the orifice will be reloaded into the inlet tube. The main body is a
vessel made up of plexiglass with dimensions of 800 × 1000 × 120 mm in width,
height, and thickness, respectively, in which about 70,000 pebbles with a diameter
of 12 mm are pre-filled. The angle of the sidewall of the vessel base is 30
◦ . Three
inlet tubes are located on the top of the vessel, where the pebbles will be dropped
through to get into the main body. A discharge orifice is located at the bottom of the
vessel, with 120 mm in diameter and 200 mm in length. The loading and discharging
rates are regulated by carriage equipment.
The particle motions are recorded by videos and images. The particle tracking
velocimetry is used for analyzing the images. In the images, every pebble occupies
about 50 pixels in diameter. As the flow rate is several particles per second, while
there are almost 70,000 pebbles in the experiment vessel, the images are acquired at
a constant rate of one frame per second.
The polished stainless black glass balls are used in this experiment to gain the
necessary resolution in measuring the particle trajectories. Under convenient illumination, each particle can reflect a small, bright, and well-defined spot, which allows
for a very precise position measurement (Fig. 2.15).
Kazuo Ohmi’s [15] algorithm is employed to find the position of each particle in
each frame. In this algorithm, the images are preprocessed to reduce the background
noise, which includes convolving the image with a Gaussian filter and an average
Fig. 2.15 Sketch of experiment setup and images. a The experiment setup. b The mean streamlines
or trajectories from nine fixed points. Five of them are marked by Nos. 1–5 corresponding to the
horizontal directions R = 0d, 8d, 16d, 24d, and30d, respectively
2 Experiments in Pebble Flows
2.5.3.1 Experimental Procedures and Methods
The experimental apparatus [17] is designed based on a real pebble-bed reactor at the
scale 1:5 (Fig. 2.15a). It runs in the way of the recirculation mode, i.e., the pebbles
discharged from the orifice will be reloaded into the inlet tube. The main body is a
vessel made up of plexiglass with dimensions of 800 × 1000 × 120 mm in width,
height, and thickness, respectively, in which about 70,000 pebbles with a diameter
of 12 mm are pre-filled. The angle of the sidewall of the vessel base is 30
◦ . Three
inlet tubes are located on the top of the vessel, where the pebbles will be dropped
through to get into the main body. A discharge orifice is located at the bottom of the
vessel, with 120 mm in diameter and 200 mm in length. The loading and discharging
rates are regulated by carriage equipment.
The particle motions are recorded by videos and images. The particle tracking
velocimetry is used for analyzing the images. In the images, every pebble occupies
about 50 pixels in diameter. As the flow rate is several particles per second, while
there are almost 70,000 pebbles in the experiment vessel, the images are acquired at
a constant rate of one frame per second.
The polished stainless black glass balls are used in this experiment to gain the
necessary resolution in measuring the particle trajectories. Under convenient illumination, each particle can reflect a small, bright, and well-defined spot, which allows
for a very precise position measurement (Fig. 2.15).
Kazuo Ohmi’s [15] algorithm is employed to find the position of each particle in
each frame. In this algorithm, the images are preprocessed to reduce the background
noise, which includes convolving the image with a Gaussian filter and an average
Fig. 2.15 Sketch of experiment setup and images. a The experiment setup. b The mean streamlines
or trajectories from nine fixed points. Five of them are marked by Nos. 1–5 corresponding to the
horizontal directions R = 0d, 8d, 16d, 24d, and30d, respectively