Probability Analysis of Velocity Distribution in a Facility of Randomly Packed Spheres Featuring Matching-Refractive-Index and Time-Resolved PIV Techniques

摘要

Complex geometries developed from a random packing produce intricate flow structures in packed bed systems. These are found in a diverse universe of multiple disciplines such as gas purifiers with petroleum engineering, chemical reactors with chemical engineering, lung tissue and other biological constructs with biological and biomedical engineering, and, rather intuitively, nuclear pebble bed reactors (PBR) with nuclear engineering.With regards to pebble bed reactors, understanding and mapping the flow is of great importance as the influence of the flow structures on transport phenomena such as heat removal is a critical factor. In the loss-of-forced-cooling (LOFC) accidental scenario, the coolant flow could be driven by the natural circulation phenomenon within the reactor core. One would expect the heat removal rate remains acceptable to the reactor design level. Therefore, it is important to gain the fundamental knowledge about heat and mass transfer within the pebble bed reactor core during the LOFC scenarios. For this purpose, multiple points or full-field measurements of flow characteristics and heat transfers at a high level of spatial and temporal resolutions are needed to fully map the complex flow patterns and to provide data at high spatial density to permit accurate volume averaging in the pebble bed. Texas A&M University is conducting isothermal measurements of pressure drops, and velocity fields in a pebble bed experimental facility to support the research on advanced nuclear reactors sponsored by Department of Energy (DOE). The main purpose of these tests is to perform high spatial and temporal resolution measurements and use the obtained results for code validation and model development. In this paper, we analyze the probability distributions of velocity experimentally measured in a facility of randomly packed spheres featuring matching-refractive-index (MRI) and time-resolved particle image velocimetry (TR-PIV) techniques. Further details of the TR-PIV measurements in the MRI facility of packed beds and flow analysis using proper orthogonal decompositions (POD) and dynamic mode decomposition (DMD) can be reviewed in .