## Fluids

#### How to define volume fraction for 3 different fluids in Multiphase model?

• Raj007
Subscriber

Hello guys,

As explained in the title, I have 3 concentric cylinders (Just like a multi-coated wire) as a geometry. I have three different fluids to specify at each inlet of cylinders.

When I use a volume fraction as 1 in phase 2 and phase 3 at inlet 2 and inlet 3 respectively. I thought I would get Phase 1 from inlet 1 because I am leaving both the phases (2 and 3)volume fractions as 0.

But as a surprise, I got the phase 2 fluid distributed from Inlet 1. Could anyone explain to me how to assign 3 individual fluids in 3 individual inlets?

Thank you

Raj

• Rob
Ansys Employee
If the three fluids don't come into contact you don't need a multiphase model. Otherwise you set the volume fraction of the first two phases and the third is whatever isn't already accounted for.
• Raj007
Subscriber
But can I specify molecular weight for the material without using multiphase model?
• DrAmine
Ansys Employee
Molecular weight is only required if you have species or dealing with phase change. If your fluids are flowing in different and separate zones (separated by walls) multiphase is not required.
• Raj007
Subscriber
I have a solid polymer as a material. At a certain temperature, the solid will change into a liquid. So, I need molecular weight. In this case, can I use a multiphase model?
• Rob
Ansys Employee
Depends if that material also interacts with the other fluids. Have a look at the solidification & melting model in Fluent.
• Raj007
Subscriber
I would like to clarify that I have separate zones (see[erated by walls) and the solid should be heated till glass transition temperature.
• Rob
Ansys Employee
Is the solid that's going to melt dividing the streams or encased in a separate domain?
• Raj007
Subscriber
it is encased in separate domain
• DrAmine
Ansys Employee
If your solid which is in separate DOMAIN will start melting you won't require a Multiphase Model in Fluent. You will require solidification and Melting model: Multiphase Approach built written a single phase approach.
• Raj007
Subscriber
Thank you for the suggestion. But I could you brief this line "You will require solidification and Melting model: Multiphase Approach built written a single-phase approach"
• DrAmine
Ansys Employee
I can do it briefly but the documentation does that in a better way. Engineers tends to solve complex problems using assumption and simplifications. The Melting model is one of these simplifications to deal with phase change between solid and liquid in an efficient way deploying a porosity approach.