Determination of conventional velocity gradient (G) using CFD technique for a pilot-scale flocculation system

Abstract

Research Article| December 01 2010 Determination of conventional velocity gradient (G) using CFD technique for a pilot-scale flocculation system Yamuna S. Vadasarukkai; Yamuna S. Vadasarukkai 1Department of Civil & Resource Engineering, Dalhousie University, Halifax NS B3J 1Z1, Canada Search for other works by this author on: This Site PubMed Google Scholar Graham A. Gagnon Graham A. Gagnon 1Department of Civil & Resource Engineering, Dalhousie University, Halifax NS B3J 1Z1, Canada Tel.: 902.494.3268 Fax: 902.494.3108; E-mail: graham.gagnon@dal.ca Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2010) 59 (8): 459–470. https://doi.org/10.2166/aqua.2010.081 Article history Received: August 26 2009 Accepted: March 22 2010 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Yamuna S. Vadasarukkai, Graham A. Gagnon; Determination of conventional velocity gradient (G) using CFD technique for a pilot-scale flocculation system. Journal of Water Supply: Research and Technology-Aqua 1 December 2010; 59 (8): 459–470. doi: https://doi.org/10.2166/aqua.2010.081 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Achieving uniform mixing conditions are essential for the flocculation process to optimize floc size and avoid floc-breakup. Limited literature is available on establishing consistent operational conditions and procedures for pilot-scale flocculation systems, which have tank sizes smaller than full-scale and larger than jar-test equipment. In this study, the influence of mixing speeds on the determination of the conventional design parameter, the average velocity gradient (G), was investigated for pilot-scale paddle flocculators. The pilot-scale plant for this paper was hosted at the J.D. Kline Water Supply Plant (JDKWSP) in Halifax, Canada. Computational fluid dynamics (CFD) was evaluated as an alternative design technique and compared against traditionally used empirical-based calculations. Comparison of both approaches showed that the G-values of empirical method were substantially higher than the predicted values for rotational speeds greater than 5 rpm. In contrast, CFD predictions found that G-values used for tapered paddle flocculation process (up to 60 s−1) could be achieved at lower rotational speed (around 15 rpm), which minimizes the power input required for mixing. The practical implications of operating at higher than required G-values relates to potential negative consequences such as floc break up, and the reliance of chemical additives to avoid floc break-up. These very practical outcomes could impact the interpretation of findings from pilot-scale treatment systems. average velocity gradient (G), computational fluid dynamics, flocculation, hydrodynamics, pilot-scale water treatment This content is only available as a PDF. © IWA Publishing 2010 You do not currently have access to this content.