Learning Forum

[hadihatami]

Hello all,nnI am trying to model CO2 being dissolved in a bubble column filled with water. For mass transfer definitions, I need to define two phases:for instance, liquid and gas, where the liquid phase includes h2o (l) and some other species, and the gaseous phase includes CO2 and air. Fluent only allows me to define material type as solid, fluid' or mixture. I define one mixture template in which I add CO2, Air, and H2O (l), but I cannot add another mixture template in which I could define similar or different species. I define a dummy phase for CO2, but inside this dummy phase I cannot define a species under Multiphase model -> Phase Interaction -> Mass -> Mass transfer -> from phase and 'species to 'dummy phase and species. nCan anyone please help me with that? I want to do this to instruct Fluent to have mass transfer from CO2 in one phase to CO2 in another phase (dissolving)?Thank you!n

[Rob]

Now you've got a species mixture alter the composition and when asked if you want to overwrite say no. That'll give you the second mixture. The interface needs an overhaul as it wasn't designed to hold two species mixtures as no-one thought about phase change when it was written. n

[hadihatami]

Thank you very much, Rob! nI had a follow up question and was wondering if you could please help me with that:if my mixture A is H2O (liq) and CO2 (g), and mixture B includes CO2 (g) and air (or a dummy CO2), I want to see how the CO2 from the gaseous phase, i.e. mixture B, gets dissolved into mixture A. But apparently Fluent only allows a mass transfer that goes from liquid phase to gaseous phase. The governing physics in my problem states that the when CO2 is injected into the water, then the mass transfer occurs by it being dissolved in the water but I think Fluent cannot model this. Should I define my mixtures any other way? nFor mass transfer, I state that from mixture A, H2O reacts with CO2 from mixture B and this yields CO2 from mixture A. n

[Rob]

I think you misunderstood the wording: it's not always clear. The mass transfer is from liquid to gas to define the positive rate. If the rate is negative it's gas to liquid. So, set up as per the documentation (which you've read - good!) but make sure the transfer is a negative value. n

[hadihatami]

Sounds good, thank you!n

[hadihatami]

I don't know if I should have made a new post or no, but I had a follow up question with regards to the chemical kinetics between the mixtures and speceis:n1- How can I define new species and radicals in Ansys Fluent? n2- Also, and more importantly, how can I define the reaction kinetics between the species I add? Should I write a UDF for that purpose? These are reactions between gaseous and aquatic phase, and is different from gas phase kinetic with the Arrhenius Law (the ones used mostly in combustion simulations)? nThanks a lot!nn

[Rob]

To create a new species just edit one that's already there and when asked to overwrite on saving it say No. Radicals are exactly the same as species, unless you add in an electric field they're just another chemical. nFor the reaction kinetics, if you're using the normal reaction (Arrhenius) just add in the various coefficients as normal. If it's a phase change reaction, read up on the Phase Interaction options and pay particular attention to the enthalpy and reference temperature. n