The Use of Particle Image Velocimetry to Study Roping in Pneumatic Conveyance

Particle Image Velocimetry (PIV) is a new technique which provides an instantaneous velocity profile of a flow field. A PIV system at Edinburgh University has been adapted to study the phenomenon of roping in a pneumatic particle conveyance rig. The principle features of this PIV system are as follows. Double images of the particles transported by the fluid are recorded on photographic film using a conventional camera. The displacement of the particle pairs, which determines the velocity at a particular point, is determined to an automatic analysis system. PIV is proving to be a powerful method in the investigation of roping. A rope is a high density ribbon of particles which is created when a uniform air‐coal flow segregates at a pipe bend into two regimes: one has a low coal to air ratio whereas the second regime, termed the rope, has a high coal to air ratio. This particular problem is connected with the pulverised fuel (pf) pipes of coal‐fired electricity generating stations. The flow, as seen on Figure 1, is reproduced in a 26 mm scale model encompassing the main aerodynamic features of pf pipes. The rope forms in the vertical to horizontal 90° bend, falls from the top to the bottom of the horizontal pipe and creats a deposit.