# Kinetic Modeling and Analysis of Fuel Element Pneumatic Lifting System in Pebble Bed Reactors
## 4 Test System and Experimental Results  
In order to study the accuracy of the fuel-element lifting-system-dynamics model, a visualization experimental platform was built. In order to facilitate observation and data acquisition, \(\varphi\)60 mm colored Plexiglas spheres were used as fuel elements in this experimental platform, and transparent Plexiglas pipes were used to build the lifting pipeline.  
Referring to the structural characteristics of the lifting pipeline of the pebble-bed reactor, several straight-pipe sections and bent-pipe sections were connected by flanges to form the lifting pipeline of the experimental platform, and the lifting height was 15 m in the experiment. The motion image of the sphere was recorded by a high-speed camera, and the gas-state parameters were collected by a manometer and a flow meter, as shown in Figure 10. The experimental equipment included a roots fan, manometer, regulating valve, thermometer, flow meter, dosing device, and diverter. The roots fan is the gas-power source, whose rated pressure is 98 kPa. The manometer monitors the gas pressure. The regulating valve regulates the flow rate of the lifting gas. The thermometer monitors the temperature of the lifting gas. The flow meter monitors the flow rate of the lifting gas. The dosing device can temporarily store the spherical components and add them to the lifting pipe accordingly. The straight pipe with an inner diameter of \(\varphi\)60 mm and the bent pipe are connected to form the circulation channel of the sphere. The diverter is used to divert the lifting airflow out of the pipeline. The collector stores the fuel elements lifted to the top.  
Figure 10: Schematic diagram of the test system.  
The roots fan is used to generate gas power. The gas flow is regulated by a regulating valve, which passes through a cooler, a thermometer, a pressure gauge, and a gas-flow meter before reaching the inlet of the dosing device. A 60 mm-diameter mock-up of the fuel element (colored Plexiglas sphere) passes through the dosing device into a 65 mm inner-diameter Plexiglas conveying duct and is driven by a continuous air flow to a collection device at a height of 15 m. The air density during the test was 1.2 kg/m\({}^{3}\) and the gas-flow rate was 9.4 m/s. To measure the running speed of the simulated parts during the conveying process, a high-speed camera recorded the motion of the simulated parts and output a series of motion images, as shown in Figure 11.  
Figure 12 shows the comparison between the theoretical and experimental values of the axial velocity of the simulated parts during the whole conveying process, and each data point is the average velocity of the simulated parts at the corresponding motion distance. When the axial displacement of the simulated part was in the range of 0-14 m, the axial velocity calculated by the kinetic model of fuel-element lifting system was in good agreement with the experimental value, with a deviation within 7%. During the experiment, when the simulated part passed through the bend (axial displacement of 16 m), the velocity dropped significantly and the experimental value deviated from the theoretical value. The reason for the deviation may be that the diameter ratio of the ball/pipe in the bend section was less than 0.92, resulting in a significant reduction in the pneumatic thrust provided by the airflow. The phenomenon can be explained as follows: as the bend pipe installed on the test platform was made from a straight-pipe section with a 65 mm inner diameter by a hot-bending formation process, the inner diameter of the local pipe was larger than 65 mm during the manufacturing process.  
Figure 11: Motion image of the simulated parts.