Numerical Study of Erosion Wear on the Disc of a Butterfly Valve With Laminar Particle-Laden Flows in a Horizontal Pipeline

Abstract

Abstract Butterfly valves are used in many processes where they mostly provide on-off control services. Many industrial processes involve fluid flows carrying particles through pipes where butterfly valves are installed. The presence of those particles produces unavoidable erosion on the valves and its study is of great importance. In this paper a numerical study of the erosion wear generated in the disc of a butterfly valve is presented. A laminar flow of water with solid particles was used. The particle-laden flow was allowed to interact following a oneway coupling. The particles felt the gravity force in the horizontal pipeline and when interacting with the pipe walls they were let to bounce right off. The gravitational effect has not been incorporated in previous studies of erosion wear in butterfly valves. To analyze how the particle-fluid interaction behavior and the gravitational force modify the erosion wear pattern, the particle Stokes number (St) and the dimensionless particle fall velocity (Sv) were varied. Without considering gravity (Sv = 0), the dimensionless erosion rates were found to reach their lowest values when St < 1. This was due to the fact that at those Stokes numbers the fluid controls the particle motion, and it moves them away from the disk when close to it. It was also found that at St >> 1 the erosion rates remain constant because the particles maintain their initial dynamics due to their higher inertia. It appears to be that the Stokes number value of one is a critical point. Similarly, when Sv is not zero, it was observed that the dimensionless particle fall velocity value of 10 appear to also be a critical point. For Sv << 10, the behavior of the impact velocity, impact angle and erosion rate were similar to the ones described of the previous study without gravity. For Sv ≥ 10, the behavior of the impact velocity, impact angle (and therefore the erosion rate) were affected by how the particles interacted with the pipe walls prior to reaching the butterfly valve disc. For very small values of St and very large values of Sv, the particles did not even reach the disc. The magnitudes of dimensionless impact velocity and impact angle have lower values at Sv < 10 and higher values at Sv > 10, thanks to the fact that gravity increased the particle velocity and forced them to bounce with the pipe before hitting the valve. For St∼1 and Sv > 10 the impact velocities and erosion rates present maximums, as a consequence of gravity transferring energy to particles as they bounce through the pipe, and to the high velocity flow near the center of the pipe that also added energy to the particles that approached it.