Weissenberg effect

{{short description|Scientific phenomenon}} [[File:Effet_Weissenberg.jpg|thumb|right|Illustration of the Weissenberg effect on a 2% solution of high molecular weight polyacrylamide]] In fluid dynamics, the '''Weissenberg effect''' is a phenomenon that occurs when a spinning rod is inserted into a solution of elastic liquid. Instead of being thrown outward, the solution is drawn towards the rod and rises up around it.<ref>{{cite web |url=http://web.mit.edu/nnf/research/phenomena/rodclimbing.html |title = Research }}</ref> This is a direct consequence of the normal stress that acts like a hoop stress around the rod. The effect is a common example of non-Newtonian fluid dynamics, which has been shown to occur for polystyrene.<ref>{{cite web |url=https://nnf.mit.edu/home/billboard/topic-5 |title = Article on the Weissenberg effect by Non-Newtonian Fluid Dynamics Group at the Massachusetts Institute of Technology }}</ref>

However, it is not always necessary to insert a rod to observe this effect. A rotating disk at the bottom of a viscoelastic non-Newtonian fluid can produce a similar phenomenon: the fluid rises at the center, whereas a Newtonian fluid forms a depression,<ref> {{cite web |title=Abstract: Viscoelastic Flow in Microchannels |url=https://absimage.aps.org/image/DFD08/MWS_DFD08-2008-000356.pdf |website=APS Division of Fluid Dynamics Meeting Abstracts (DFD08) |publisher=American Physical Society |date=2008 |access-date=2025-11-11 |language=en |type=Conference abstract }}</ref> as seen when stirred with a magnetic stirrer. [[File:Magnetic Stirrer.JPG|thumb|right|200px|A Newtonian fluid forming a depression when stirred with a magnetic stirrer.]] The height of the fluid at the center increases with both the rotational speed of the disk and the elasticity of the fluid.<ref> {{cite web |title=Abstract: Viscoelastic Flow in Microchannels |url=https://absimage.aps.org/image/DFD08/MWS_DFD08-2008-000356.pdf |website=APS Division of Fluid Dynamics Meeting Abstracts (DFD08) |publisher=American Physical Society |date=2008 |access-date=2025-11-11 |language=en |type=Conference abstract }}</ref> The effect is named after Karl Weissenberg who published about it in 1947.<ref>{{cite journal |last=Weissenberg |first=K. |date=1947-03-01 |title=A Continuum Theory of Rhelogical Phenomena |url=https://www.nature.com/articles/159310a0 |journal=Nature |language=en |volume=159 |issue=4035 |pages=310–311 |doi=10.1038/159310a0 |pmid=20293529 |bibcode=1947Natur.159..310W |issn=1476-4687 |url-access=subscription }}</ref>

== References == {{reflist}}

== External links == * [http://www.bsr.org.uk/weissenberg/3/Isolation%20of%20Weissenberg%20Effect.htm The Isolation of, and the Initial Measurements of the Weissenberg Effect]

Category:Viscosity Category:Rheology