Learning Forum

[yusuf uzun]

Hi,

I am trying to simulate Multiphase CHT problem. In my case, there are two fluids, air and water. I want to simulate water side as a Multiphase Mixture Model. Heat is rejected from air to water so I should simulate water side with airside but i can't define air side's cell zone conditions as air material. I tried to define air as a secondary phase(with vapor) but the air has became transformable to vapor and from water. Then analysis diverged. How can i define air material without defining as a phase?

[Rob]

To clarify, to the two fluids interact or are they kept separate in that the water is on one side of the wall and gas on the other? 

[yusuf uzun]

Fluids are kept separate. There is wall between fluids.

[Rob]

OK, that's single phase. Turn off the multiphase model. Make sure you have two fluids (air & water) and set the cell zone(s) to the appropriate material. 

[yusuf uzun]

Thanks for the answer. I guess you understand wrong. Probably i couldn't explain clearly. My problem's simplified schematic is like in attached picture below. I can't define and analysis single phase and multiphase fluid at the same time in fluent.

[Rob]

OK, you need multiphase. The water side is two phases, water & gas. Gas is probably a species mixture of air & water vapour. The air side is also multiphase but will be all gas, and all air. I'd skip the air side if possible and focus on just the boiling to start with. 

[yusuf uzun]

Water side consist of water(liquid) and water(vapor).

Yes, air side is multiphase now but i want to define air side as a single phase. If there is no phase change in air side even air side defined as a multiphase, it can be acceptable.

Also i should simulate the air side because air side provides heat to water side. How can i simulate single phase air and multiphase water together?

[Rob]

You don't. You set air side as "air" species from the "gas" phase. Or do a lot of reading around system coupling to run two Fluent sessions: which you can't with Student. 

[yusuf uzun]

So, Fluent software can't model Single phase and Multiphase fluids together except system coupling. Do i understand wrong?

[Rob]

Yes and no. Fluent can model gas (only) on one side and both phases on the other. But the gas side is still multiphase. 

[yusuf uzun]

Can i make air can't changing phase while air is multiphase? If i can do that, my problem will be solved.

[Rob]

If you don't tell air it can change phase then it won't. The only phase change setting will be (barring some extreme conditions) 

Water(liquid) to water(gas). 

Water(gas) and air(gas) are a species mixture, and assuming you have no reactions or other phase change mechanisms set air isn't going to do anything other than heat up & flow. 

[yusuf uzun]

I didn't define reaction and phase change mechanism between air and other phases(just water and vapor phase change mechanism). But air transform to water and vapor with iterations. With more iterations amount of air in domaine decrease a lot and most of them transform to water and vapor (mostly vapor).

[Rob]

Check the boundary conditions.