Influence of structuredness on the pressure drop through a packed pebble bed
Barnard, Franco Cecil
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During this study an experimental test facility was designed and constructed with the purpose of conducting experiments to measure the pressure drop through packed beds of spheres with varying levels of structuredness. The test facility had to be designed so that the uncertainty in the measured friction factors would be below ±10% and commissioned to ensure that results with an acceptable degree of accuracy could be obtained. Experiments were done on a randomly packed bed and a structured packed bed in order to demonstrate the proper operation of the test facility. The resulting experimental data was compared with applicable correlations found from relevant literature. The nuclear safety standards commission (KTA (1981)) correlation, as well as the relation of Ergun (1952) was chosen for comparison with the experimental data obtained from the experiment on the randomly packed bed. The correlation of Wentz and Thodos (1963) was selected for comparison with the experimental data obtained from the structured packed bed experiment. The friction factors obtained from the experimental data was found to be higher than the friction factors calculated with the different correlations for the respective packing configurations. This could be attributed to the manufacturing process of the packing configurations that resulted in the surface finish of the particles to be extremely coarse. In order to obtain the desired porosity within the structured packed bed, cylindrical rods were utilised to separate the particles to prevent contact between them. Wentz and Thodos (1963) also made use of cylindrical rods, called distention rods, to make varying porosity possible within the structured packed beds. The cylindrical rods that were utilised during these experiments are larger (in diameter) than those described in the literature, which could have contributed to the higher pressure drop through the structured packed bed. Furthermore, it was found that the friction factors derived from the experimental data increased as the modified Reynolds number was increased. This is a phenomenon that is not fully understood at this time and further study is proposed. The operation of the experimental test facility was successfully demonstrated. The measurements were shown to be repeatable and the uncertainty of the friction factors derived from the measured data obtained from the test facility was less than 10%, which is satisfactory. Therefore, the ability to measure the pressure drop through packed beds of spheres with varying degrees of structuredness has now been established as a result of this research.
- Engineering