CBE - Development of a Viscoelastic Normal Stress Measurement Probe

Normal stress differences are a hallmark of many complex fluids, from food materials to polymer melts and industrial suspensions. When a rod rotates in such fluids, elastic stresses can cause the well-known “Weissenberg effect,” where fluid climbs up the rod. In recent classroom demonstrations, we observed an unexpected and potentially useful variation of this effect: a hollow rotating tube causes fluid to rise inside the tube significantly higher than the external rod climb when the lower end is brought near a boundary.

This project will investigate whether this phenomenon can form the basis of a simple and inexpensive device for measuring normal stresses in viscoelastic fluids. Students will measure fluid rise inside and outside rotating tubes, examine the effect of bottom-wall proximity, and test how tip geometry and tube diameter affect the response.
Students will gain hands-on experience in experimental design, fluid mechanics, rheology, and quantitative data analysis. Depending on interest, students may also contribute to theoretical modeling or comparison with classic results on rod climbing and hoop-stress–induced pressures. The long-term goal is to determine whether this effect can be turned into a practical “normal stress probe” for laboratory or educational use.