[Tleja]

Hi everyone!

I'm new in multiphase field. I have one question about unit of source. I have learned about source term and UDS for many week, And found that unit of source term should be kg/m^3.s basically. At the moment, I study in Multi-phases system.
my system consists of gas and solid phase.

In gas phase, there are 2 species (A,B).
In solid phase, there are 2 species (C,D).

Actually, I need to add source term of A,B species into gas phase in fluent by using UDF.
Right now, i'm quite confused which unit of A source term i should define. In my understanding, I'm not sure about which unit between "kgA/m(g)^3.s" or "kgA/m(g+s)^3.s".

Which volume should i divide by??? (gas volume or total volume)

Best Regard
Tleja

[pakk]

I think your real question has nothing to do with units... The unit is kg/m^3.s, there is no such thing as "m(g)" or "m(g+s)", a meter is a meter.
The question you have is, I believe, on how you should calculate the number to put into Fluent.

Suppose you have the following numbers:
Total amount of A that should be generated: 0.01 kg per second.
Total volume where you apply the source: 0.1 m^3.
Total volume of your model: 1 m^3.
Total volume of the room where you sit in: 20 m^3.
Total volume of my apple: 0.0001 m^3.

Which volume should you take? The relevant one. That is obviously not your room and not my apple, but I understand you might doubt if you need the total volume or the volume where you apply the source.
One way to think about this: what would happen if you would add a 'dead volume' to your simulation? Your answer should physically stay the same. But that 'dead volume' would increase the total volume of your model, so that should not be the answer.
Another way to think about this: If you have a source of X kg/m^3.s, and you apply it to a volume 0.1 m^3, the total amount of A that is generated is 0.1 X kg/s. So, if you want 0.01 kg/s to be generated, you should choose X equal to 0.1. In other words: your source should be (0.01 kg/s)/(0.1 m^3) = 0.1 kg/m^3.s.

[Tleja]

Hi Pakk!

Thank you for your reply

Firstly, i'm so sorry for my not clear question.

Let you see my picture please. http://postimg.org/image/v0x8x7ebt/

As my picture, I was defining source term for H2 in gas phase.
In my understanding, if i select source term for gas phase, i think that Unit of all species source term in gas phase may be kg(species)/m(volume of gas)^3.s

That is my question. i'm not sure Which volume is m^3 in picture based on?

Cell volume or volume of gas?

Best Regard
Tleja

[pakk]

What is your kg(species)? The mass that should appear in the cell? Or the mass that should appear in the volume? As long as you choose the same reference for the mass as for the volume, it does not matter. It will be exactly the same number.

[Tleja]

Hi Pakk

Thank you so much for your knowledge

best regard
Tleja