Scale growth study in a concentric reducer: Measurement of instantaneous velocity using Particle Image Velocimetry

A series of experiments were conducted at Queensland Alumina Ltd to study the rate of Gibbsite scale formation on wall pipes.. "Gibbsite scale growth in pipe fittings is a major problem for an alumina refinery. A recent investigation into the scale growth mechanism at an alumina refinery found almost 60 % more scale growth in a reducer when compared with the connecting straight pipe sections for similar flow conditions. Scale growth occurs where liquor (supersaturated solutions) come in contact with solid surfaces and it is affected by the liquor flow velocity besides other physical and chemical parameters. The present work is dedicated to study the hydro-dynamical aspects of the mechanism of scale growth. In particular, the role of the phenomenon of turbulent bursting, stream wise and cross stream fluctuating velocity components (Ux and Uy) was investigated as the flow moves through the reducer. Particle Image Velocimetry (PIV) technique was used to get a full view of the reducer and the readings close-to-the-wall of the reducer at Reynolds number of 27,000 and 44,000 upstream which corresponds to Reynolds number of 41,500 and 66,000 downstream of the reducer respectively. The results showed an increase in cross stream and a decrease in magnitude of stream wise fluctuating velocity components, whereby we presume that the increased cross stream fluctuating velocity component increases the frequency of impacts of the scaling particles on the wall thus initiating excessive scale growth in the reducer when compared with the connecting straight pipe sections, for similar flow conditions." -- abstract