Editing Mixing (process engineering) (section)

===Close-clearance mixers===
There are two main types of close-clearance mixers: anchors and helical ribbons. Anchor mixers induce solid-body rotation and do not promote vertical mixing, but helical ribbons do. Close clearance mixers are used in the laminar regime, because the viscosity of the fluid overwhelms the inertial forces of the flow and prevents the fluid leaving the impeller from entraining the fluid next to it. Helical ribbon mixers are typically rotated to push material at the wall downwards, which helps circulate the fluid and refresh the surface at the wall.<ref>{{cite web |url=http://www.bakker.org/cfm/webdoc10.htm |title=Helical Ribbon Impeller |publisher=Bakker.org |date=1998-04-10 |access-date=2017-06-23 |url-status=live |archive-url=https://web.archive.org/web/20170814180054/http://www.bakker.org/cfm/webdoc10.htm |archive-date=14 August 2017 |df=dmy-all }}</ref>