Meshing water pipeline alimentation.
 

Greetings, im a mechanical engineering student. I was wondering if you can give me advise selecting the right mesh for my thesis project, im working in a water treatment plant; 1 of the modules have a problem in which he dont get the amount of water it should. There are 4 modules, the total of mass flow is around 1250 lps, where approximately 5% of this mass flow is air, so the diamater of the pipe if 20 inches.
Im going to use the mixture model, this with the idea of that the air is a compound, that represent around 78% nitrogen, 21% hydrogen and 1% others gases. With that idea on mind i know that the hydrogen travels dissolved on the water, but this is not the case for the nitrogen; additional is well know that the pumps are of low pressure, high flow rate and the temperature environmental; 0,7-0.9 psi, 300-320 lps per pump 4 in parallel and 25° c respectively.
So get to the point, i was thinking on use a sweet method with an inflation of the first layers to get the job done; maybe use the sharp tool with interfacial anti-diffusion? that could help?
Do you guys thinks this arrangement will do the job or there is other better? obviously i was thinking on work half of the pipe, i really want to reduce the calculation time; is there is another better option i will be thankful.