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-   -   variable composition mixture (http://www.cfd-online.com/Forums/cfx/109154-variable-composition-mixture.html)

amin_gls November 10, 2012 09:54

variable composition mixture
 
hi guys
i want to explicitly set density for a variable composition mixture ,what should i change in cfx pre to be able set it manualy . by default cfx determines density by mass fraction ..
thanks so much .. :rolleyes:

ghorrocks November 11, 2012 06:09

Can you explain what you want to do? The density of multi component mixtures is already determined by the solver from the density of the compoenents and their mass fractions. What do you need to explicitly set?

amin_gls November 11, 2012 07:47

thanks glenn. i know it that density is determined by solver , i have a variable composition mixture ,copper and h2so4 .i dont want to determines density by solver ,in ANSYS CFX-Pre User's Guide , in chapter 24 in topic variable composition mixture and mixture properties tab i read it {When you create a fixed composition, variable composition, or a reacting mixture, then the fluid properties are
determined by mass averaging the properties of the component materials. In some cases, the ideal mixture rule used
by the CFX-Solver may not be representative of the mixture properties. You can override the individual
thermodynamic and transport properties by enabling the appropriate toggles and directly specifying the mixture
properties
. For details, see Mixture Properties (Fixed and Variable) (p. 36) in the ANSYS CFX-Solver Modeling guide }
i need to specify directly the density of mixture .
just this . how? i dont know!!!.
thanks if you can help me.

ghorrocks November 11, 2012 17:18

The multi component model is designed for mixtures of gasses. You appear to have a solute and a liquid - is this correct? Copper dissolved in H2SO4 (Please correct me if I am wrong).

cfdonlineuser November 11, 2012 21:33

Why don't you just use a single material for the mixture eg water and set the density directly to a constant value as you require. Alternatively set the mass fraction to zero for one of the species then the other species density becomes the mixture density

amin_gls November 13, 2012 11:40

Quote:

Originally Posted by ghorrocks (Post 391520)
The multi component model is designed for mixtures of gasses. You appear to have a solute and a liquid - is this correct? Copper dissolved in H2SO4 (Please correct me if I am wrong).

thats right .

ghorrocks November 13, 2012 21:31

For solar salt bath heating (which seems similar to your application) a typical approach is to use an additional variable to model the salt concentration and make th density a function of the AV. Would this approach work for you?

amin_gls November 29, 2012 10:50

thanks .. i want to simulate buoyancy in a box that there is a source of copper in one wall and a sink in another
the material between this two wall is variable composition material ..
if i use additional variable ror copper . is the buoyancy force calculated ?

ghorrocks November 29, 2012 17:18

Not by default, I think. You will need to include a function for the material density as a function of copper concentration.


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