[thomasduffy001_]

I am currently modelling my thesis in ANSYS Fluent and I am facing some issues regarding species transport. Unfortunately no lecturers at my university are familiar with Fluent so I have had to teach myself the program and it is extremely difficult for me to troubleshoot at times.

Some background knowledge on my topic and simulation is described as follows. I am conducting my thesis on the numerical modelling of plasma liquid interfaces for medical applications. I have three predominant aims: determine the steady-state temperature profile, the steady-state velocity profile, and the chemical species concentration gradients at the gas-liquid interface. In FLUENT my model is 2D axisymmetric and involves a jet (containing a mixture of gaseous chemical species)*impinging onto a small volume of water; with the remainder of the domain surrounded by atmospheric air. I am utilising a three-phase Eulerian model with air as my primary phase, a gas-mixture as one of my secondary phases (containing OH, H2O2, NO, NO2, N2O4, HNO2, and HNO3), and a water-mixture which consists primarily of water with aqueous species. The aqueous species in the water are produced by 2 means; interfacial mass transfer from Henry's law (i.e. phase change of each chemical species) and chemical reactions occurring within the water region itself. At this stage, I am purely focusing on the interfacial mass transfer as I am getting unphysical results.

For the purpose of troubleshooting, I am only considering one mass transfer mechanism at the moment (between gaseous nitrogen dioxide and aqueous nitrogen dioxide). My mass transfer mechanism is species-mass-transfer, using Two Resistance Model, Henry's Law as the equilibrium model option, Molar Fraction Henry Coeff, vant-hoff correlation with ref. Henry constant as 0.034 and temperature dependence as 1900K (this is from a recommended source from FLUENT). The "FromPhase" Interface mass transfer was set as zero-resistance, and the "ToPhase" Interface mass transfer coefficient was specified as ranz-marshall.

I have attached photos of my problem below; the first one shows the 3 Eulerian phases (the gas mixture within the jet, the water and the surrounding air). The second photo shows that after a small time, the gaseous no2 is being converted into aqueous no2 within the jet region which is incorrect. How can I enforce a condition to make the mass transfer occur only at the gas-liquid interface?

[Ahmed Alkaisi]

You have to use a udf file for species transport to define the relative humidity and the mass transfer
Try 2 phases first ignore the air phase