Paper Number
IN20
Session
Flow-induced Instabilities in Non-Newtonian Fluids
Title
Diving into yield stress fluids
Presentation Date and Time
October 12, 2022 (Wednesday) 4:25
Track / Room
Track 5 / Sheraton 2
Authors
- Geri, Michela (Massachusetts Institute of Technology, Department of Material Science and Engineering)
Author and Affiliation Lines
Michela Geri
Department of Material Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02141
Speaker / Presenter
Geri, Michela
Keywords
experimental methods; theoretical methods; consumer products; flow-induced instabilities; foams; food rheology; suspensions
Text of Abstract
Many foods, cosmetics, building materials, petroleum derivatives, adhesives, foams, and even soil or snow can be categorized as yield stress fluids, showing a complex, time-dependent rheological behavior that strongly affects the way they flow. In industrial settings, it is often necessary to have a quick and reliable way of measuring the “consistency”, or strength, of these semi-solids products without the need to use a rheometer. The standard method adopted extensively across industries for such measurements makes use of what is known as a “penetrometer”: a device that releases a cone of given weight on top of the material of interest and measures the total penetration depth after the cone reaches equilibrium. Inspired by such simple yet effective device, in this talk we will explore the dynamics of an object diving into yield stress fluids. By resolving the displacement evolution over time for different forcing weights and different object shapes, we will show how the rheological behavior of the material affects the fluid dynamics during diving. We will focus on both simple and thixotropic yield stress fluids across industries, e.g., paraffin gels, hair gels, shaving creams and butter. Combining the experimental observations with appropriate constitutive relations and fluid modeling, we will finally elucidate how the time-dependent rheological parameters, especially plastic viscosity and static/dynamic yield stress, can affect the transient flow before the diving object reaches its final equilibrium position.