On the role of micro- and mesomixing in a continuous Couette-type precipitator

Precipitation of barium sulphate in the annular gap of a continuous Couette reactor with two unpremixed feeds has been experimentally investigated. Th e experiments have been carried out in the turbulent regime with an axial R e-x varying from 100 to 240; the hydrodynamics can be described with the pl ug flow plus dispersion model, and in the condition tested the Peclet numbe r varied from 2 to 6. The initial supersaturation has the strongest effect on both the particle size and the crystal morphology. The average size of t he crystals is also influenced in some cases by the diameter of the feed tu be and by the feed velocity, indicating the relevance of mesomixing. The ro tation velocity has a relatively weak effect on crystal size and CSD, but a maximum has been observed increasing the rotation velocity. The performances of the system have been predicted in the limit cases of mi nimum and maximum age mixedness as a function of the Peclet number. (C) 199 9 Elsevier Science Ltd. All rights reserved.