Experimental study of graphite particle deposition upstream of a forward-facing step

Multilayer graphite particle deposition was experimentally investigated upstream of a forward-facing step (FFS) in stationary flows in order to better understand graphite dust contamination in HTR primary circuits. Stationary flows of ambient air with homogeneously dispersed graphite particles were created in a small-scale low-speed horizontal flow channel (SSHFC). Flow field measurements were carried out by means of Particle Image Velocimetry (PIV). The FFS-Reynolds numbers ReS determined for the flow scenarios under consideration were in the range of 610–6000. The thickness of particulate deposits created in front of the FFS was measured spatially resolved in regular time intervals by means of laser triangulation. Gravitational settling and inertial impaction accounted for the majority of particle deposition right upstream of the step. Both volume and shape of particulate deposits were observed to depend on local flow characteristics as well as on the size distribution of the used graphite particles. The bulk density of particulate deposits increased with increasing ReS and with increasing mean graphite particle size. The amount of particles adhering to the front side of the FFS due to inertial impaction decreased with increasing Stokes number.