Inter-layer distance optimisation for a light-based flowmeter by means of CFD

A non-intrusive method to measure the particle velocities in dilute-phase pneumatic conveying is described. The method is based on correlating signals, which are measured in two flow cross-sections. The cross-correlation function generated provides information about the time it takes for a particle to travel between the measurement planes. Knowing the inter-plane distance and the time delay, the particle velocity can be calculated. The two measurement planes must be an optimum distance apart to ensure the best possible signal resolution and sufficient quality of the cross-correlation: If the distance is too small, the resolution is coarse, while for a too large distance, the pipe contents in the two crosssections may differ due to curved particle trajectories (e.g. due to gravity), leading to weak crosscorrelation functions. In this paper, experimental measurements and Computational Fluid Dynamics (CFD) simulations of dilute-phase pneumatic conveying processes are reported. Particle trajectories for a given pipe geometry and different conveying velocities are used to estimate an optimal inter-layer distance.