Heat and dust transport in a pebble bed HTR

The flow behavior in pebble bed reactors is typically analyzed using lumped parameter or porous medium approaches. Such approaches inhibit averaging of flow quantities over large volumes. The ever increasing computational power and advanced numerical CFD methods allow a more detailed assessment of the flow behavior, and especially the heat and dust transport in a pebble bed. The first part of this paper discusses Large Eddy Simulation results of the flow and heat transport in a randomly stacked bed of spherical pebbles, using a second-order accurate, cell-centered finite volume method on an unstructured polyhedral mesh. The predicted flow-field is fairly complex and exhibits highly unsteady and three-dimensional turbulent behavior with strong rotational and cross flow regions. The reported analyses results can be used for validation of low-order turbulence modeling applications to complex pebble flow configurations. While Large Eddy Simulation is a more accurate methodology to study the flow and heat transport, it becomes impractical to use it for dust transport studies due to large computational costs in tracking several thousands of dust particles individually. Owing to this limitation, the second part of this paper focusses on Reynolds Averaged Navier Stokes modeling of flow and dust transport in a random pebble bed arrangement. The dust transport model used in the present study is validated across two test cases of flow over single and array of spheres where reference experimental data are available. Finally, this validated model is used to analyze the dust transport and deposition patterns in a randomly stacked pebble-bed arrangement.