Learning Forum

[SR786]

Hi,

I want to set up an MRF Case for an unbaffled stirred tank reactor agitated by a magnetic rod stirrer. The tank is unbaffled and open at the top. I have attached an image of the set-up along with the boundary conditions.

For MRF stirrer BC, do I need to define a moving wall for the stirrer in the rotating zone or can I keep it stationary. Also similar question, do I keep the rest of the BC as stationary walls too?

 

[SR786]

For instance here, for the impeller can I keep the BC as a stationary wall or do I need to define the wall as "Moving relative to the adjacent cell zone with 0 RPM". Similarly for the side-walls and bottom can I keep the BC as stationary or do I need to define them as "Moving in the absolute velocity frame with 0 RPM".

[Rob]

I can't see images in the second post. 

The stirrer walls should move at zero rpm relative to the cell zone, which should be rotating at whatever speed you want. Side & bottom can be stationary as their fluid region won't be moving. 

[SR786]

Hi,

Apologies the images didn't render properly. So the stirrer (inside the MRF) is defined as moving wall with 0 RPM relative to the cell zone. Whereas the side wall and bottom (outside the MRF) can be left as stationary walls.

[Rob]

Correct. What is wall-int ? The mrf should be an interior. 

As it's an unbaffled tank you could set a single fluid zone with moving walls on the mixer (as you have) and the tank walls as either stationary or moving at absolute rpm of zero. 

[SR786]

 

I didn’t update the name, it’s meant to be side-wall. 

The reason why I want to use MRF over SRF is because whilst the current unbaffled mixer is operating in batch, I intend to model precipitation reactions in the mixer which are operated continuously (so inlets and outlets will be added to the model). Due to the addition of these stationary components, MRF would be better than SRF in transitioning from batch mixer to semi-batch/continuous mixer.