how to change the material properties
 

Hello

Can somebody tell me how to change the material properties in cfx? For example, the standard water phase is at 25C, how can I change to water @ 1C? What properties of water do I need to change?

Are there tutorials talking about this?

Thanks in advance!

Marco

Re: how to change the material properties
 

Hi,

I'm not sure, but I think there aren't tutorials showing how to change the material properties. However, in the documentation, there's a whole chapter about materials: CFX-Pre, Materials and Reactions.

What properties you need to change? It depends on what equations you're solving. Take a look at those equations and see what properties are there. If you want to solve just the hidro-dynamic equations, and if your water is at 1 ºC, you could change the water density and the viscosity. But the water density at 25 ºC is nearly the same as at 1ºC, and it would be probably enough to change the viscosity.

To change some property, in CFX-Pre edit the material properties and change what you want.

Re: how to change the material properties
 

Hi, Rui

Thank you. I think you are right, changing the viscosity may be sufficient for my case

I am just curious that why the cfx developers did not consider this. It should be very easy for them to include some relative database in code.

Regards!

Marco

Re: how to change the material properties
 

It has been considered. That's why there are so many materials available in CFX already. Mabye you did not hit the "..." button on the materials panel.

Neale.

Re: how to change the material properties
 

Sorry, Neale, I did not find the '...'button you mentioned. Which version are you talking about? I am using cfx5.7.

What I expect is to be able to quickly input a temperture, then the code can automatically renew the material properties. Or the code allows to has temperature options, say 1, 2, 3...

I guess this may be not available in cfx. But I think such a function should be useful for many people.

Regards!

Marco

Re: how to change the material properties
 

Sorry, not "...". On the materials tab hit the little icon on the right side which has a picture of an open folder. There are many materials.

It is hard to simply "build in" a library as you say because this does not exist. To do what you say requires picking an equation of state. Which do you suggest?

Or, why don't you just create an ideal gas and then set the heat transfer model to isothermal (to set the temperature you want). This will still leave rho = f(p) but that will be as close to what you want I think.

Or was your material a liquid. If so, then your kinda screwed. There are not many well known equations of state for liquids.

Neale.

Re: how to change the material properties
 

Thanks, Neale.

It may be difficult to have such a library for all the liquids or gases, but should be possible for water. In most of the Fluid Mechanics books, there are tables for the physical properties of water at different temperature. If these tables can be included in code, it would be convinient for the users.

Regards!

Marco

Re: how to change the material properties
 

Yes, you could use the liquid water defined in the Redlich Kwong library then. This is what you need. It has variable properties as a function of temperature. You still have to run isothermal to get the right value of density.

It could be a bit "whizzier" in that the GUI could ask you for a reference state and then simply use the equation of state to evaluate the properties at that point. Which is really what you are asking for.

Neale.