Experimental verification of a CFD model intended for the determination of restitution coefficients used in erosion modelling

Abstract

Erosion caused by solid particles transported with the steam or flue gas has a negative impact on the power unit reliability and availability. The erosion rate depends inter alia on the restitution of the particle velocity upon impact. The restitution coefficients determine the angle of the particle reflection off the tube surface and the particle post-impingement velocity, i.e., they determine the direction of the particle path, which has a substantial impact on the erosion phenomenon inside the tube. An attempt is made herein to develop a method of determination of restitution coefficients by means of numerical modelling assisted by experimental testing on physical models that will be implemented further in the Ansys Fluent code. Such a numerical procedure will verify the model of erosion caused by particles of iron oxides. The erodent impingement angle α₁, the impingement velocity w₁, and the reflection velocity w₂ are measured using the Casio High-Speed Exilim EX-F1 camera, which enables filming at a high rate. The film is then processed graphically for “frame-by-frame” tracking. The following erodents were used in the testing: iron oxides, quartz sand with a different grain size (490, 1000, 1500, 2000 μm), and 1000 μm-diameter steel balls. The steel balls, due to their ideal shape, were treated as the comparative analysis reference standard. Erosion of three types of 5x10 cm plates was tested: a plasma-coated plate with an anti-erosion layer, an aluminium plate; and a steel sheet plate. Based on the restitution coefficient testing results, numerical simulations were performed of the particle reflection off the surface.