Particle visualisation - a tool for determination of rise velocities

Abstract

Particles from a post denitrifying Kaldnes Moving Bed Process were studied using an optical borescope, a visualisation technique that provides opportunities for both qualitative and quantitative studies of the separation mechanism in Dissolved Air Flotation (DAF). Rise rates for particle/bubble aggregates were estimated showing great variability. Two groups of aggregates were distinguished; relatively small flocs (<100 microm) with single bubbles attached rising comparatively slowly and large flocs (>100 microm) with several bubbles attached rising very fast. The high rise rates for large aggregates are discussed, possibly explained and suggested as the reason for the effective separation of large particles noticed in previous studies. Removal efficiency of different size categories of particles in DAF were investigated on the basis of particle size analysis indicating increased separation efficiency with increasing particle size.

A Novel Hybrid Scheme for Making Feasible Numerical Investigations of Industrial Three-Phase Flows with Aggregation

“…The predicted aggregate diameters for the test case (shown in Figure ) are in the approximate range of 250–450 μm, which is significantly larger than the diameters of the constituents (cf. Table ) and compares with values for DAF units. , The unsteadiness due to the turbulent motion of the bubble plume is visible in the instantaneous snapshot.…”

“…Table 1) and compares with values for DAF units. 15,30 The unsteadiness due to the turbulent motion of the bubble plume is visible in the instantaneous snapshot.…”

Ballasted Flotation with Glass Microspheres for Removal of Natural Organic Matter

“…The explanation relates to the microsphere numbers required to achieve suitable rise velocities. Typical floc rise velocities of bubble-floc aggregates have been measured between 3 and 15 m h À1 (19,20). Based on flocs having an average diameter of 500 mm, with a conservative density of the flocculated material of 1050 kg m À3 and assuming that the flocs are spherical in nature and obey Stokes' law, for a target rise velocity of 6 m h À1 only 12 of the bigger, lower density SI 100 microspheres would need to be contained in the floc.…”

Determination of Actual Object Size Distribution from Direct Imaging

“…Two acrylic columns having internal diameters of 25 and 140 mm are used. A rigid borescope [22][23][24][25][26][27][28][29][30][31] (Olympus) with a 60 o field of view and 0 o direction of view is used to obtain particle images in a dynamic system. The borescope has a diameter of 6 mm and length of 250 mm.…”