Describing Rheological Properties of Unknown Materials - In-Class Activity (Spring 2015)
Explore the rheological properties of unknown materials in a hands-on in-class activity. Students work in teams to identify whether samples are pseudoplastic, Newtonian, or dilatant fluids based on viscosity changes with shear rate. Corn syrup, corn starch, icing, and toothpaste are analyzed, with findings including shear-thickening behavior and yield stress indications. Teams also create shear stress vs. shear rate curves to further analyze fluid flow characteristics.
Download Presentation
Please find below an Image/Link to download the presentation.
The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author. Download presentation by click this link. If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.
E N D
Presentation Transcript
Spring 2015 BE 191 1 In-Class Activity Describing the Rheological Properties of Unknown Materials
Spring 2015 BE 191 2 Instructions, Part 1 Assemble into teams of 4 or 5 at a dry erase board or table. Work as a team to feel, pour, squish, squeeze, ..., and deform the four materials (A-D) provided to your group. As a team, identify whether each of your samples is a pseudoplastic/shear- thinning (n <1), Newtonian (n = 1), or dilatant/shear-thickening (n>1) fluid. = shear stress (Pa) y = shear yield stress (Pa) K = flow consistency index, units of Pa sn = shear rate (s-1) n = flow behavior index: n n < < 1for a pseudoplastic fluid n n = 1 for a Newtonian fluid n n > 1 for a dilatant fluid Also, try to guess what each fluid is! Their smell might give the away. t =ty+Kgn h = Kgn-1 eff ? ?
Spring 2015 BE 191 3 Answers, Part 1 Corn syrup (Sample A) is a viscous, Newtonian fluid. Its viscosity (~3.6 Pa*s) does not change with shear rate. Corn starch (Sample B) is shear- thickening. Its apparent viscosity is increasing with shear rate. Icing (Sample C) is a shear-thinning, or pseudoplastic, fluid. Its apparent viscosity is decreasing with shear rate. = shear stress (Pa) y = shear yield stress (Pa) K = flow consistency index, units of Pa sn = shear rate (s-1) n = flow behavior index: n n < < 1for a pseudoplastic fluid n n = 1 for a Newtonian fluid n n > 1 for a dilatant fluid Tooth paste (Sample D) is similar to icing; it s shear thinning. t =ty+Kgn h = Kgn-1 eff ? ?
Spring 2015 BE 191 4 Instructions, Part 2 Next, your team should prepare a figure containing estimated shear stress vs. shear rate curves for each of the materials you were given. One of the materials in your possession is similar to a Bingham plastic in that it has a yield stress. Clearly indicate this fluid s yield stress in your plot. = shear stress (Pa) y = shear yield stress (Pa) K = flow consistency index, units of Pa sn = shear rate (s-1) n = flow behavior index: n n < < 1for a pseudoplastic fluid n n = 1 for a Newtonian fluid n n > 1 for a dilatant fluid HINT: Your plot will not look like the one to the right! Really think critically about how each of your fluid samples flows. How viscous is it? When does it flow? How easily does it flow? t =ty+Kgn h = Kgn-1 eff ? ?
Spring 2015 BE 191 5 Corn syrup is a viscous Newtonian fluid. Its flow curve should be a straight line. Answers, Part 2 Corn starch is shear-thickening. At increasing shear rates, this suspension behaves more like a solid, only deforming under ever-increasing shear stresses. Corn starch Icing At most shear rates, icing has a higher apparent viscosity than the tooth paste. The tooth paste has a yield stress of ~15- 30 Pa; when applied shear stress is below this yield stress, it does not flow. Tooth Paste = shear stress (Pa) y = shear yield stress (Pa) K = flow consistency index, units of Pa sn = shear rate (s-1) n = flow behavior index: n n < < 1for a pseudoplastic fluid n n = 1 for a Newtonian fluid n n > 1 for a dilatant fluid Corn Syrup t =ty+Kgn h = Kgn-1 eff ? ?
