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Old   May 8, 2012, 21:21
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Glenn Horrocks
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The 4 iterations was not necessarily the cause of the clipping error. It was just a bad idea which CAN cause lots of problems so is best removed.

Soldification models in CFX are not supported as a release option to my knowledge. I know people have done it and there might be beta options to help but I am not sure. You will need to talk to CFX support for details on this.
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Old   May 9, 2012, 00:44
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glenn, i did send a mail to LEAP AUTRALIA and they replied ;

" You treat the material as a single fluid but have Cp(T), rho(T), mu(T) which allows you to have different properties either side of the phase change boundary. To make it work you don't change phase at a single temperature but across a small temperature range, just as would happen if you have a mushy zone. "

here comes the problem that how should i define these properties as a function of temperature. for that reason i tried "if statement" or the second option was to do in fortran and add it in my external library. But the version available here does not have "cfx5ext.h" in ansys files.
What is your opinion about preparing a fortran file, would that be workable idea?
Thanks
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Old   May 9, 2012, 07:26
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No, apply these functions as 1D interpolation functions. No need for fortran.
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Old   May 9, 2012, 17:42
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I dont think so that linear function can be made for phase change, for specific heat its ok as pure metals have almost constant cp.But for density and viscosity, linear functions cant work(bcoz of enthalpy chnage).m i right?
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Old   May 9, 2012, 18:42
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The whole idea of using just the material properties to model phase change is an approximation. Things like latent heats, superheat/subcool, spinondal temperature/attainable limit of superheat etc cannot be accounted for with this approach. If parameters like this are important for your model then you will probably find this approach is not going to work.

But if they are not important it might work - it is up to you to determine the error involved in this simplification.
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Old   May 9, 2012, 19:09
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Yes, as i already told you that my problem involves phase change so that's why i am reluctant to use this approach.
Hey glenn, i have generated another output file this time i guess there are no significant errors apart from phase chnage(as it dint work yet).Could you please have a look at it.Thanks
Attached Files
File Type: zip outputRUN4.zip (91.2 KB, 4 views)
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Old   May 10, 2012, 00:50
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I have few questions like;
> There are some tutorials such as (spray dryer, steam jet) where (air + steam/water) is present and phase change is also occuring EVEN WITH MULTICOMPONENTS INVOLVED. Can I use the same approach for my problem?
> I have defined an opening boundary where opening temp is set 2427C which is actually the temperature of that sprayed molten metal droplet. I was curious that why cant i set the temperature of air (25 C) as opening temp. And in solver during monitor point graph (variable value and accumulated time step),
if opening T = 2427C, there is no chnage in scale along variable axis
if opening T = 25 C , it varies.
I have attached both graphs, strange thing is liquid droplet temp, which is 2427C while graph shows its 2700C . Could you please have a look at it.
Thanks
Attached Images
File Type: jpg opening temp2427C.jpg (30.9 KB, 6 views)
File Type: jpg user point run 5 (opening temp25C).jpg (32.2 KB, 3 views)

Last edited by Danial Q; May 10, 2012 at 01:11.
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Old   May 10, 2012, 06:42
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Your question has now become "how do I do advance phase change modelling in CFX". I think this is too difficult a topic to discuss on the forum.
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Old   May 10, 2012, 18:21
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My problem is same as I stated earlier, the point to mention spray dryer and steam jet is, if I can use the same approah for my problem? I just wanted your opinion to make sure that I was thinking in a right direction.Thanks
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Old   May 10, 2012, 23:49
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Sorry, I do not understand the question. Can you phrase it more clearly?
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Old   May 11, 2012, 00:54
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I mean to say that is it posiible that i could use the same approach for phase chnage ,as used in steam jet or spray dryer cases. Though in those case, its evaporation phenomena but as far as phase change is concerned it might work for me as solidifcation. Because in cases (steam jet and spray dryer) total three phases are involved (air + H2Ovap + H2Oliq). While in my case, (air + liq metal + solidmetal). do you think this evapration cases can be used as anology for phase chnage application????

Last edited by Danial Q; May 11, 2012 at 04:50.
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Old   May 11, 2012, 07:11
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While the spray dryer tutorial is a 3 phase model, it is three very different phases to yours. Details make all the difference in multiphase models. In the spray dryer you have solids (modelled as lagrangian particles), liquid water (modelled as a variable on the particles) and gas (air and water vapour). You are trying to model 3 phases with a eularian model. Totally different. And the phase change model used in the spray dryer has almost nothing in common with what you need for solidification.

And the steam jet is only a 2 phase model (liquid and gas), but the gas is a multicomponent gas (air and water). Again, very little in common with your application.

You need to find an example which models solidification in a eularian/free surface model. It will be complex in CFX as there is no built in model for it.

I was playing with Fluent today and noticed its solidifcation model. I have no idea if it is appropriate for you, but I suspect you will have more luck with that compared to CFX where no solidification model exists.
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Old   May 12, 2012, 02:49
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Thanks, it is clear now. well so i am in hell of a situation here.while my mentor believes that this model is possible in ansys cfx. anyhow, another suggestion i got from some one is about defining (air+ liquid metal) as a mixture (binary; which i totally disagree) even though a mixture seems useless option to me whether its variable, fixed or ideal. Am I right?

Yea, I started to learn Fluid too for the purpose, but again problem is getting properties data for Ni at those high temps to define its properties as function of temp.Again, density in fluent is also defined by "Peng Robinson eq." ,even other choices (presented models) need some critical propeties and i found Fluent more tricky than CFX. so din't spent that much time on that.good luck to me, its my first year project in phd and year is almost over.

Thanks.
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Old   May 13, 2012, 07:07
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Quote:
my mentor believes that this model is possible in ansys cfx
Possible - yes, it is. Others have modelled it. Is it easy - no. There is no built in model for it, so you are going to have to develop the model yourself.

Can I recommend you do some study and familiarise yourself with exactly what multiphase and multicomponent means. It is best if you understand what these models actually imply then you can answer your question in red by yourself.

Don't have material properties? Then you need JMatPro (http://www.sentesoftware.co.uk/home.aspx). It has all the material properties you need for just about any alloy you can about. But it is expensive unfortunately - but do you want comprehensive material properties or not?
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Old   May 13, 2012, 18:32
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Thanks. Developing model by myself...? Do you mean selecting right options while setting physics or writing some program files... ?

As far as ,multiphase and multicomponent is concerned, in my opinion, multiphase flow involves different phases of fluids on macroscopic scale only (single fluid with two phases or two/more fluids with different phases), and muticomponent implies the fluid containing different types of components on molecular scale( e.g air contains multicomponent, or smoke contains multicomponent normally etc.) correct me please, if i am wrong.
And in my case, i am pretty sure that it is homogeneous multiphase flow, involving two pure fluids (air & Ni). so, ideal mixture assumption for air and nickle ,in my opinion is out of question. Correct me if i am mistaken.
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Old   May 13, 2012, 18:37
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Develop the model by yourself means applying through the use of source and sink terms to create and destroy stuff, and do all the coupling to the energy equation yourself. How much of this is relevant depends on the physics of your model, and it is up to you to determine that.

You understand the difference between multiphase and multicomponent. And your comment about the ideal mixture assumption is correct.
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Old   May 13, 2012, 20:15
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It seems like some diplomatic statement .well, and to do all this what could be helpful literature should i study or work on.

Thanks Glenn, you have been really helpful.
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Old   May 16, 2012, 20:47
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Could you please give me some advice that how to define temperature range. I mean should I generate expressions or I have to do some CCL editing stuff. any document or references??
I tried "if statement" with (T >= 1500) e.g and it worked up to some extent, i got considerable results. But for sake of accuracy , it would be good if i could do that by defining range.

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Old   May 16, 2012, 20:56
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Sorry, I do not understand your question. What do you mean by "if statement" worked to some extent? What do you mean by defining a range?
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Old   May 16, 2012, 22:35
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I used this "if statement" to define temperature and regarding values of properties. And i want to define a range for these values like from 1000 to 2000 K. i have attached graphs to show that this statement worked as properties changed as my expectations. here is the statement;

if( T >= 1727 [K],7780[kg m^-3], 8115[ kg m^-3]).
here i want to define range for T (1000-2000).
Thanks
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File Type: jpg T vs Den Chart.jpg (33.5 KB, 8 views)
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