Number of the records: 1
The effect of shear rate on aggregate size distribution and structure at steady state in laboratory and pilot plant scale
- 1.
SYSNO ASEP 0378884 Document Type C - Proceedings Paper (int. conf.) R&D Document Type The record was not marked in the RIV Title The effect of shear rate on aggregate size distribution and structure at steady state in laboratory and pilot plant scale Author(s) Bubáková, Petra (UH-J) SAI, ORCID, RID
Pivokonský, Martin (UH-J) SAI, ORCID, RID
Pivokonský, Radek (UH-J) SAI, ORCID, RIDSource Title Proceedings of the International Conference on Particle Separation. - Berlin : IWA, 2012 / Jekel M. Pages s. 28-35 Number of pages 8 s. Action IWA Specialist Conference on Particle Separation Event date 18.06.2012-20.06.2012 VEvent location Berlin Country DE - Germany Event type WRD Language eng - English Country DE - Germany Keywords aggregation ; aggregate size distribution ; flocculation ; fractal dimension ; shear rate Subject RIV BK - Fluid Dynamics R&D Projects IAA200600902 GA AV ČR - Academy of Sciences of the Czech Republic (AV ČR) CEZ AV0Z20600510 - UH-J (2005-2011) Annotation The paper deals with the dependence of aggregate properties on the shear rate (G) at steady state. Natural raw water and ferric sulphate were aggregated in a laboratory Taylor-Couette reactor (TC) and continuous flow mixing tank (MT) with a paddle stirrer (pilot plant). The shear rates in the range of approximately 20-350 s-1 were used and the mixing time corresponded to 15 min (steady state). The methods of image and fractal analysis were used to determine the aggregate size and structure, respectively. It was found that the maximum steady state size of aggregates produced by both mixing devices was almost identical and ranged approximately from 7800 μm at G ~ 20 s-1 to 245 μm at G - 300 s-1. In the case of the average aggregate size, there was a little difference at G ~ 80 s-1 when the aggregate size in MT was higher than in the TC device. A new relationship which describes the dependence of aggregate size on the shear rate was proposed. It takes into consideration the finite values of aggregate size at extreme values of shear rates. The D2 fractal dimension was found to increase from 1.54 to 1.91 in TC and from 1.58 to 1.90 in MT with increasing shear rate indicating that the aggregates became less porous and more compact. Moreover, the very precise match in D2 values was attained for both mixing devices. The D pf fractal dimension decreased from 1.37 to 1.10 in TC and from 1.36 to 1.12 in MT with increasing shear rate, which means that aggregates were more regular at higher shear rates but jagged on the surface with irregular shape at lower shear rates. On the contrary to D2, aggregates formed in MT were much more irregular or jagged than those formed in TC. Workplace Institute of Hydrodynamics Contact Soňa Hnilicová, hnilicova@ih.cas.cz, Tel.: 233 109 003 Year of Publishing 2013
Number of the records: 1