Learning Forum

[SR786]

Hi I am modelling mixing of a tracer in water (two liquids miscible with one another) in a batch stirred tank based on an experiment using the species transport model. I have followed the usual steps which include:

1. Computing flow field for primary liquid (water) using steady state solver & standard k-epsilon turbulence model.
2. Activate species transport model, create mixture template for tracer & liquid. Assume tracer has same properties as bulk liquid & change diffusivity from default value to diffusivity of tracer in liquid.
3. Patch small volume of tracer into computational domain.
4. Freeze flow field, switch off flow & turbulence equations (solve only for one species transport equation). Activate transient solver.
5. Create monitors of concentration at several locations in the tank, run simulation and estimate mixing time(s).

Prior to starting my simulation, I notice after patching the initial concentration of tracer (t=0) is ~1.64 kmol/m^3. For the experiment, the concentration of tracer is 0.51 kmol/m^3. How do I change the concentration of tracer so it exactly matches the concentration used in the experiment?

[Rob]

Replot with node values off: the mesh looks very coarse in that region so you may not be patching into as much of a volume as you think. 

The patch is a mass into a volume. So, if you need a certain concentration you need to back calculate the mass into that volume to give the volume fraction. Note, in your experiment you add a known mass into the system, not a known concentration into a region of the tank. 

[SR786]

No worries, thank you for the suggestion!