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-   -   How to simulate a passive scaler transport? (https://www.cfd-online.com/Forums/cfx/250696-how-simulate-passive-scaler-transport.html)

Angkon July 4, 2023 12:04
How to simulate a passive scaler transport?
 
Hi, I want to acquire concentration profile(concentration gradient) iodine injected into blood within left coronary artery, here iodine is the passive scaler and I only need to consider advection diffusion through blood i.e. non-reactive process.
Here boundary conditions that are applied for blood flow are:
1) No slip boundary condition at artery wall,
2) Pulsatile velocity and pressure profile at inlet and outlet respectively, using udf.

I am confused how to define the passive scaler or which module should I use : CFX or Fluent, what should I use multiphase or multispecies or user defined scaler or 'the species option in fluent'. how do I define the source of the scaler what mole fraction should I use?

Thank you in advance.

ghorrocks July 4, 2023 20:40
CFX and Fluent both have the capability to model this.

Multiphase, multicomponent or user scalar? In Fluent use a user scalar. In CFX use an additional variable.

How to define the source? Many options: maybe a boundary condition, maybe a source term, maybe a source point.

What mole fraction? Note the scalar may not be in units of mole fraction. If the scalar is unreactive then you might as well just define it as 1 at the injection point and then everything is just a ratio from that.

Angkon July 5, 2023 08:54
Quote:
Originally Posted by ghorrocks (Post 852777)
CFX and Fluent both have the capability to model this.

Multiphase, multicomponent or user scalar? In Fluent use a user scalar. In CFX use an additional variable.

How to define the source? Many options: maybe a boundary condition, maybe a source term, maybe a source point.

What mole fraction? Note the scalar may not be in units of mole fraction. If the scalar is unreactive then you might as well just define it as 1 at the injection point and then everything is just a ratio from that.
Thank you for your response,
is there any tutorial that can be helpful for my case?

ghorrocks July 6, 2023 04:41
I cannot recall if any tutorials use additional variables. Have a look and see. Don't forget to look at the tutorial and examples on the ANSYS Customer site as well, there are many more there.

Gert-Jan July 6, 2023 10:14
look in this forum on 'residence time' and you wil lfind how to do this, since the approach is similar.

Opaque July 6, 2023 16:40
Quote:
Originally Posted by Angkon (Post 852827)
Thank you for your response,
is there any tutorial that can be helpful for my case?
Check the CircVent Tutorial. it uses an additional variable to trace "smoke"

Angkon July 11, 2023 00:53
Quote:
Originally Posted by Opaque (Post 852939)
Check the CircVent Tutorial. it uses an additional variable to trace "smoke"
Thanks for your response,
can you please tell me where I can get this tutorial?

Angkon July 11, 2023 00:57
Quote:
Originally Posted by Gert-Jan (Post 852918)
look in this forum on 'residence time' and you wil lfind how to do this, since the approach is similar.
I need the information of how the concentration changes all over the geometry within a certain time period starting from the inlet, is it related to 'residence time'?

ghorrocks July 11, 2023 02:56
The tutorial is one of the tutorials in the CFX documentation. Have you looked in the documentation?

The residence time example Gert Jan gave was an example of how to use additional variables. We are recommending you use an additional variable approach in your case as well, but just as a convecting scalar.


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