The effect of shear rate on properties of aggregates formed in the water treatment process

0378896 - ÚH 2013 HU eng C - Conference Paper (international conference)
Bubáková, Petra - Pivokonská, Lenka - Pivokonský, Martin
The effect of shear rate on properties of aggregates formed in the water treatment process.
Proceedings of the 6th IWA International Conference for Young Water Professionals. Budapest: IWA, 2012, IWA-9867.
[IWA International Conference for Young Water Professionals /6./ (IWA YWPC 2012). Budapest (HU), 10.07.2012-13.07.2012]
R&D Projects: GA AV ČR IAA200600902
Institutional research plan: CEZ:AV0Z20600510
Keywords : aggregate size * fractal dimension * shear rate * water treatment
Subject RIV: BK - Fluid Dynamics

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. The shear rates in the range of approximately 20-350 s^-1 were used and the aggregation 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 aggregate size decreased with increasing shear rate. There was a small difference in sizes of aggregates formed in TC and MT at G < 150 s^-1, but at higher shear rates, almost no difference between TC and MT was observed. The D₂ fractal dimension increased 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 with increasing shear rate meaning that aggregates were more regular at higher shear rates, but jagged on the surface with irregular shape at lower shear rates. Contrary to D₂, aggregates formed in MT were much more irregular or jagged than those formed in TC.
Permanent Link: http://hdl.handle.net/11104/0210217