Rheology

 
Lecturer: Prof. Dr.rer. nat. Ronald Gebhardt
Contact: Rheologie.SMP@avt.rwth-aachen.de
Lecture: 2 hrs
Tutorials: 2 hrs
Course schedule: Please get them from the Course calendar RWTH Online
Lecture notes: Available on Moodle
Quality Improvement Fund: The lecture (exercises) is funded by Quality Improvement Funds. For more information on the use, visit the website of Faculty of Mechanical Engineering.
Semester: Summerterm
Language: German
Exam: Written Exam

In process engineering processes, liquid systems are used in many cases. These systems usually exhibit both elastic solid-state behaviour and viscous liquid behaviour. In contrast to low-molecular liquids, complex phenomena such as the change in viscosity with increasing mechanical load occur. The aim of the rheology lecture is to understand these effects in order to be able to predict how a fluid system will behave under different process conditions.

For this purpose, shear rate and shear stress profiles of ideal fluids in simple shear flow, pipe flow, laminar film flow and in a stirred reactor are considered and the findings are then transferred to non-ideal fluids. In order to understand the effects that occur in these cases, the fundamentals of colloidal systems, i.e. the structures present there as well as the prevailing interactions and solubility properties, are discussed. In detail, the concepts of ideal and real conformation of long polymer chains for suspensions are worked out and the scale laws based on self-similarity of polymers with corresponding critical exponents for osmotic pressure and characteristic sizes and concentrations are discussed.

For the description of dynamic properties of polymer systems, on the other hand, mechanical models are used, which consider for polymers, for example, beads consisting of several subunits connected by Hook's springs. In addition to the basics of viscosity measurement, students are also taught model approaches to describe the concentration dependence of the viscosity of suspensions and emulsions on the one hand, and to determine the intrinsic viscosity, i.e. the polymer contribution to viscosity, from concentration-dependent measurements on the other hand.

After the introduction of the stress and velocity gradient tensor, the flow law will be generalized in order to be able to use it for any flow in three-dimensional space. In addition to shear stresses, normal stresses, which can be assigned to the elasticity of visco-elastic materials, are also dealt with. Finally, oscillation, creep and relaxation tests are discussed as time-dependent shear tests. Such tests can be used to determine the proportions of elastic, plastic and viscous deformation, as they occur, for example, after a specific deformation of the material. The different deformations can be assigned to basic elements such as springs and dampers, which can then be combined in mechanical models to model complex material behavior.