Particle trapping and deposition around an obstacle occurs in many natural and industrial environments. In the nuclear industry, for instance, the steam generator of a nuclear power plant is a heat exchanger where a turbulent multiphase flow (water, steam, and solid particles) goes through a bundle of tubes supported by plates. These plates induce local perturbations that cause particle deposition. This progressive obstruction of the flow, i.e. a clogging phenomenon, reduces the efficiency of the steam generator and can induce tube cracking leading to breaking and damage. The steam generator then loses its role as safety barrier of the nuclear power plant.

From a fundamental standpoint, dilute and concentrated particulate flows have received a growing attention in the last decade. Of particular interest is the behavior of particle flow around obstacles and particle trapping by obstacle wakes. The aim of this study is to achieve a better understanding of the hydrodynamic contribution in the clogging phenomenon, and in particular of the particle transport around obstacles in confined flow.

To accomplish this goal, experiments were performed in a simplified configuration by considering a laminar flow (20 < Re < 400) in a vertical tube with a square section. An obstacle (a step or a square cylinder) was inserted at the middle height of the tube and neutrally-buoyant particles were injected at different locations along the tube. We have investigated first the trajectories of individual particles and then the dynamics of a suspension of particles, using PIV (Particle Image Velocimetry) and PTV (Particle Tracking Velocimetry). The particle trajectory were modeled by using the Boussinesq-Basset-Oseen equation and either measuring the flow velocity fields around the obstacle by PIV or calculating it by the Code_Saturne software (Free, open-source software developed and released by EDF: https://www.code-saturne.org/cms/) in order to account for the 3D character of the obstacle wake (Re>90).

We present a comparison between the experimental observations and the predictions of the modeling for both obstacles (step and square cylinder) at steady flows and low Reynolds numbers (< 100).