[oliveira1820]

I want to study the density and temperature variations of 2 fluids: air (gas) and Zinc Nitrate solution (liquid), and the heat transfer between them and with the solid around. They are in the same reservatory and buyoncy is considered.

I´m considering a single fluid domain where there are the 2 fluids with 0,875 Zinc Nitrate and 0,125 air. There is a point source that heats the system and will reflect on evaporation of zinc nitrate and, therefore, the mixing of air and zinc nitrate.I want to study with detail the evaporation and when it happens, and also the density variation in each point.

I´d like to know which Fluid Models / Fluid Specific Models / Fluid Pair Models I should consider and why.

Can anyone clarify me on this matter?

Thanks!

[ghorrocks]

What state does the air/Zn Nitrate Solution exist in? Air bubbles in a continuous fluid? Big air bubbles or small air bubbles? Or maybe a foam? Or a slurry? Something else? Does the Zinc Nitrate start becoming a solid as it dehydrates?

[oliveira1820]

The fluids are in a niobium cyclotron target and at the beginnig the target is completly full with gaseous air and liquid zinc nitrate solution. Before the proton beam hits the target is there is 0,875 nitrate solution on the low part and 0,125 of gaseous air on the top, cause of buyoancy density difference

When the proton beams hits the target, there is a great amount of heat in the target reflecting in the vaporization of zinc nitrate and gaseous mixing with air. There is no foam or slury and the fluid may condensate when touches the walls cause of the water cooling on the outside and evaporates again when heated. Note that never gets to solid due to the great continuum amount of heat

The heat is constant cause the proton beam hits the target during all the experience. There is always great turbulence cause of this.

[ghorrocks]

Please correct me if I am wrong, but it sounds like the initial condition is a well defined free surface, and then the beam hits it and rapid boiling occurs which is likely to cause the fluids to explode into bubbles all over the place and then condensation occurs on the outer walls as they are colder. Is this correct?

If this is correct it sounds like a seriously difficult simulation to me. It involves several different types of multiphase flow, in addition with boiling and condensation. The boiling may be fast enough to be non-equilibrium just to make things even harder.

Are you aware of how difficult a simulation this is likely to be?

[oliveira1820]

That is correct, the initial coniditon corresponds to a well defined free surface.

But i wasn´t expecting that will be that hard to simulate this.

I want to do the closer to reality simulation possible, what Fluid Models / Fluid Specific Models / Fluid Pair Models should I use?

Also, do you know works similar to this or tutorials?

What advices and suggestions can you give me?

[ghorrocks]

There are lots of tutorials on all the models in the ANSYS customer webpage.

But I would not recommend a simulation like this be attempted unless you are an experienced CFD operator. None of the available models appears to capture what you are trying to do directly, you are going to have to adapt an existing model to handle multiple physical states, or at least states outside its intended regime - this is why it is not a simulation for beginners.

Maybe you should think about simplifying your model so you only model physics relevant to the results you need to get. That will depend on what why you are modelling this - what do you intend to learn from the CFD?

[oliveira1820]

- I would like to study the hat transfer between the solid target and the water surrounding cooling system

- I would like to study the nitrate solution vaporization and density variation in each point

- I would like to study the pressure in the target
in relation to the heat source quantity.

[ghorrocks]

How fast does the target heat up? How hot does it get? How big is the target?

How does the nitrate affect the vaporization? Does it crystallise out?

[oliveira1820]

The target heats very quickly, maybe in some miliseconds, we´re talking about niobium with a 16MeV energy beam.

The temperaure it gets I have no idea but I think its some hundreds of ºC, and its 35mm of dimmension with between 0,8 and 10 mm thickness,depending on the target part.

The way nitrate affect the vaporization is one of the goals of the study, and I suspect it crystalizes to Zinc Oxide but only with a great amount of time and the cristalization can be despised.

[ghorrocks]

"Quick" is a relative term. If your target heats in milliseconds that is slow enough that you might be OK with equilibrium boiling. I am a MEMS designer and we heat the fluid to 300C in about 400ns - that is plenty quick enough that it is non-equilibrium boiling.

If you look at equilibrium boiling of water (or other simple fluid) under the heating effect that is a simulation which is likely to be possible in a reasonable amount of time. I would put the effect of the nitrate and other chemistry off for future work. Just getting the boiling working well on a simple fluid will be a big challenge in itself.

The ANSYS customer page has a few examples of boiling modelling, so that would be the place to start. There are more examples available from your ANSYS support person.