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-   -   Which Multiphase Model?Ethylene glycol+Silver nanoparticles (http://www.cfd-online.com/Forums/cfx/108610-multiphase-model-ethylene-glycol-silver-nanoparticles.html)

fshak92 October 28, 2012 14:33

Which Multiphase Model?Ethylene glycol+Silver nanoparticles
 
I'd like to model a combination of ethylen glycol and silver nanoparticles .(the combination lies on a solid plate and then heats)

The viscosity of ethylen is in order of 1 cP but the combination of that should become about 70 cP.

I dont know which kind of multiphase flow models is appropriate for this modeling and how i can find out the characteristics of the combination after setting up the multiphase flow.(like boiling point and etc. )

thank you in advance.

ghorrocks October 28, 2012 17:10

nanoparticles are too small to model with a multiphase model. I would consider modelling this with an additional variable for the nanoparticles, and make all the material properties functions of the nanoparticel concentration.

fshak92 October 29, 2012 07:58

Quote:

Originally Posted by ghorrocks (Post 388972)
nanoparticles are too small to model with a multiphase model. I would consider modelling this with an additional variable for the nanoparticles, and make all the material properties functions of the nanoparticel concentration.

Thank you for the reply.
Do you know any related paper or book or link regarding these issues?
you mean i should define just a user-defined fluid and try to define all the variables as functions of my nanoparticles?
I know just the percentage of nanoparticles in the ethylen glycol and the variables(characteristics) of the final mixture.

ghorrocks October 29, 2012 17:13

There are a few posts on the forum about nanoparticles. You will need to do a literature search to find what the state of the art is, however.

Quote:

you mean i should define just a user-defined fluid and try to define all the variables as functions of my nanoparticles?
Yes, that is what I am getting at but you have not explained what you are trying to do so cannot be sure this is the best approach.

But you can forget about multiphase models as things like interphase slip and heat transfer do not happen, instead Brownian motion and things like that are important. Brownian motion can be modelled as diffusion on an additional variable.

evcelica October 31, 2012 12:47

A agree with Glenn,
You need to tell us more about what you are trying to do. Is the combination always at the same mixture concentration, or are they mixing? Are you trying to boil the ethylene glycol away and leave the silver particles?

fshak92 November 5, 2012 08:12

1 Attachment(s)
Thank you for your attention.

Yes i like to boil the ethylene glycol and leave the silver particles.

I want to have heat transfer simulation of the sintering process.
In this process, a moving laser beam heats a high-visous fluid(mixture of ethylen glycol +silver nanoparticles) on a solid plate .

As you see in the picture below, there are 2 blocks.the bigger one(blue one) is solid plate. and the other one(green one) is the high-viscous fluid.
A laser beam should heat the top part of the fluid line(high-viscous fluid).

So my first problem, as i asked above, is that how can i model that high viscous fluid? Because the charactristics of the fluid should be changed by temperature changes.

And my second problem:
I think i cannot use the 'heat flux BC' because my 'fluid line' is not solid and i cannot set any constant BC on the topwall.furthurmore i should probably consider melting and it's the other reason that i cannot use the heat flux BC.
So i dont know how can i heat the 'fluid line' by a moving laser beam.

I hope i could clarify my problem.
Thank you in advance.

evcelica November 5, 2012 20:24

I am not experienced in these types of models, or the sintering process, so I can not help you much. But like Glenn said, you can make a user material and use a function to change your material properties with temperature, or the additional variable, or both.

I would think the laser beam would not only affect the surface, but would penetrate into the volume of the fluid, and perhaps onto the surface of the plate underneath. You can do this with source terms where you define a Z coordinate which will change along the length with time. Then use some expressions like step functions to add a volumetric heat source to all the fluid volume or plate surface within a distance (radius of your laser beam).

As far as boiling away the fluid, and leaving the particles behind I can not help you there, sorry.

ghorrocks November 6, 2012 06:44

This is a really complex model. I hope you are expecting to take several months on this (if you are experienced at CFD) or a few years (if you are a beginner). You are going to have lots of physics sub models to develop and validate, then combine them together and validate again.

But a question - how much fluid flow is involved in this? It seems the paste just sits there and gets cooked, so very little flow actually happens. If this is the case then you would probably get just as good answers with a simple heat equation solver linked to some lumped physics parameters for the sintering. If fluid flow is not significant then do not do this with CFD, it will just make it a zillion times harder.

fshak92 November 15, 2012 06:06

Quote:

Originally Posted by ghorrocks (Post 390536)
This is a really complex model. I hope you are expecting to take several months on this (if you are experienced at CFD) or a few years (if you are a beginner). You are going to have lots of physics sub models to develop and validate, then combine them together and validate again.

But a question - how much fluid flow is involved in this? It seems the paste just sits there and gets cooked, so very little flow actually happens. If this is the case then you would probably get just as good answers with a simple heat equation solver linked to some lumped physics parameters for the sintering. If fluid flow is not significant then do not do this with CFD, it will just make it a zillion times harder.

Thank you for the replies.

Yes the movement of fluid is not considerable because of its high viscousity and the heat transfer part is significant.
I would appreciate if you explain more about the ways you mentioned above.

ghorrocks November 15, 2012 06:26

It sounds like you need to look at what the fundamental physics at work here is. If fluid flow is not significant then forget about CFD software. The physics is much easier to model if you assume things do not move, then a simple heat transfer model with some phase change physics can do it. And they can often be written by hand.


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