Measurement of instantaneous flow velocities in a concentric reducer using Particle Image Velocimetry: Study of scale deposition

Abstract

Deposition of scale (dispersed solids) on the walls of pipework of process plants is a serious maintenance issue. A study conducted at an alumina refinery has revealed a phenomenon of a substantial increase in the rate of scale deposition on the walls of a concentric reducer when compared to that for adjacent straight pipes. To explain this phenomenon the measurement of instantaneous velocity fields in a liquid passing a concentric reducer has been undertaken using Particle Image Velocimetry (PIV). The variation of both the stream-wise and cross-stream components of the fluctuating velocity ( u x ′ and u r ′ respectively) in the proximity of the wall in the scale model of a concentric reducer has been measured. It has been found that the cross-stream component of the fluctuating velocity, u r ′ varies significantly as flow passes through the concentric reducer. At a Reynolds number of 43,740 and at the distance from the wall of 0.05 R ( R is the radius of the pipework) the component u r ′ in the reducer becomes five times greater than that at the walls of the straight pipes connected to the reducer. Such a variation in the near-wall u r ′ may be accountable for the increase in gibbsite scale deposition rate observed on the surface of a concentric reducer.