John Flashcards
1
Q
Write a brief account of the considerations (related to rheology) required during the design process of:
- Mixing of toothpaste in a stirred reactor
- Crude oil flowing in heat exchanger network
- Extrusion of slurries/pastes into catalytic pellets
A
- Toothpaste is a Bingham fluid, a type of purely viscous, meaning inelastic, fluid. These types of fluids behave as a solid until the critical shear rate is achieved, after which they will begin to flow.
Graphs and equations, conventional and herschel-bulkley - Crude oil in a heat exchanger is a time dependent fluid, more specifically it is thixotropic. The shear flow properties depend on both the rate of shear, as well as the time of shearing. Crude oil thins with time, so when sheared at a constant rate of shear following a period of rest, the apparent viscosity gradually decreases as the internal structure is progressively broken down.
- Extrusion of slurries/pastes into catalytic pellets is viscoelastic, meaning that in addition to viscous behaviour, this fluid also exhibits some elastic behaviour. Generally contain elastic particles which are stretched during flow but which recoil when the stress is reduced. Display the Weissenberg effect and Due swell
