Learning Forum

[SR786]

Hi, I am modelling mixing of two miscible fluids (water & tracer) in an agitated vessel where I want to monitor the concentration profile of the tracer over time at several locations in the vessel. The tracer is inert so no chemical reactions need to be considered. Also the vessel is operated in batch so there are no inlets or outlets (tracer injection is instantaneous).

To do this I have activated the species transport model and created a mixture template for the water & tracer (tracer & water have same properties). I can see that a new equation has been added for the tracer.

However I do not know what other steps I need to do before running the simulation, i.e., how do I define the region of cells occupied by the tracer in the tank at the beginning?

[Rob]

Have a look at registers to then patch the tracer. It's been covered several times on here, and may well be included in Learning. Check the species mixture diffusivity is correct as it's often overlooked. 

[SR786]

Hi,

Thanks for the reply! So essentially once I've activated species transport and modified the mixture template for water & tracer (same physical properties) and also changed the diffusion term, I then need patch a small volume in my domain which represents the tracer injection (mass fraction of 1) using adapt/cell registers/region. For my boundary conditions, a species BC is enabled automatically where a mass flux can be specified. Do I need to specify the mass flux as there are no inlets or outlets in my domain (I am assuming this is what its purpose is for?)

[Rob]

Leave wall bc's alone as you're just looking at the tracer flow. You may also want to look into running the flow steady state and then running just the tracer as transient. No reason to solve the whole lot transient if it's the same material properties: look at Solution>Control>Equations and do some reading. 

[SR786]

Thank you, also one final question. How do I designate the concentration of tracer as I want to add 0.5 mol/L?

[Rob]

You're adding a volume fraction, but depending on the size of the region (check the volume in Fluent's reports as registers aren't a precise volume) so you may need to do some thinking to get the correct mass or fraction.