A smart chemical reactor: Mixing in a Taylor-Couette Reactor with Axial Flow

Wolf-Gerrit Fr üh

Heriot Watt University, Edinburgh

email: [email protected]

• What is it?

• Why bother with it?

• What needs to be done – and how?

What is a Taylor-Couette reactor?

• A rotating cylinder within a stationary cylindrical tank.

• Mixing provided by rotation of inner cylinder • Operating controls: – Flow rates and – Rotation rate • Batch or continuous operation In continuous operation: reactants input at base or distributed; product extraction from top

Why should we consider it?

• Forcing is by moving wall but flow is governed by global hydrodynamic instability  Uniform mixing throughout bulk of fluid  Uniform mixing/reaction conditions • Ideal both for batch and continuous operation.

• Easy to control: – only rotation rate – and flow rates of fluids • Easy to maintain and clean (Just take the inner cylinder out … )

Flow types

Depending on the rotation rate and flow rate: • Laminar rotational Couette and axial Poiseuille flow • Propagating Taylor vortices • Wavy propagating Taylor vortices • Turbulence • And many more…

Propagating Taylor vortices

• Batch operation, or if vortices move with mean flow  separate cells, moving with mean flow, each with specified life time • If they move faster of slower  winding axial stream 6 U ax =0.0

6 U ax =0.7

6 U ax =1.4

6 U ax =2.1

6 U ax =2.8

5 4 5 4 5 4 5 4 5 4 3 2 3 2 3 2 3 2 3 2 1 1 1 1 1 0 0 0.5

x 1 0 0 0.5

x 1 0 0 0.5

x 1 0 0 0.5

x 1 0 0 0.5

x 1

Demonstration of mixing

Laminar Turbulent 0.04

0 0.02

0.04

0.02

0 0 1000 2000 3000 0 0 0.2

0.5

0.4

0 0.3

0.2

0.1

0 0 1000 t (s) 2000 time 3000 0.15

0.1

0.05

0 0 0.04

0.02

Vortices stationary in tank 1000 2000 3000 0 0 1000 t (s) 2000 0.05

0.04

0.03

3000 0.02

0.01

0 0 1000 2000 3000 Vortices moving slightly faster than mean axial flow 1000 t (s) 2000 3000 from: A. Syed and W.-G. Früh (2003).

Journal of

Chemical Technology and Biotechnology 78 , 227–235.

What needs to be done – and how?

• Establish local and global mixing behaviour for range of flow conditions – Detailed simultaneous velocity and concentration measurements – Direct numerical simulation • Develop a design tool to predict outcome by characterising flow type – Extension and validation of advection-dispersion model of linked stirred-tanks system