[Weiqiang Liu]

Hi all,

I am writing source terms for my governing equations in fluent. All the source terms occur because of chemical reaction. I have a question that is do I have to define mass source term after I have defined all species source term. As far as I am concerned, the pure mass source is just the summation of all species source terms. Therefore, I want to ask is it necessary to define mass source after all species sources have been defined?

Best regards.

Weiqiang.

[LuckyTran]

No mass source. Chemical reactions don't change mass.

[Weiqiang Liu]

Originally Posted by LuckyTran

No mass source. Chemical reactions don't change mass.

I do have mass source term. Because one of my reactants is carbon which is a user defined scalar. Therefore the mass source term for fluid is just the consumption of carbon.

[LuckyTran]

Originally Posted by Weiqiang Liu

I do have mass source term. Because one of my reactants is carbon which is a user defined scalar. Therefore the mass source term for fluid is just the consumption of carbon.

consumption of carbon does not mean mass is consumed (mass is not created or destroyed in this process).

To give another example, if steam condensed into liquid water, or if liquid water is converted into solid ice, then there still is no mass sources/sinks. There is a source/sink in the transport equation for phase though.

If carbon suddenly appears or disappears via reactions that's a change in in species mass/mole fractions (just like change in phase), but mass is not changed.

[Weiqiang Liu]

Originally Posted by LuckyTran

consumption of carbon does not mean mass is consumed (mass is not created or destroyed in this process).

To give another example, if steam condensed into liquid water, or if liquid water is converted into solid ice, then there still is no mass sources/sinks. There is a source/sink in the transport equation for phase though.

If carbon suddenly appears or disappears via reactions that's a change in in species mass/mole fractions (just like change in phase), but mass is not changed.

but in my case, carbon is solid which is not one part of fluid. I defined soot local mass concentration as an UDS. According to this, the mass of fluid in the system is not conserved.

[LuckyTran]

Then you have a surface flux, not a volumetric source. Surface fluxes don't go in the governing equations, they go in the boundary conditions.


For example: in a velocity inlet, there is no mass source even though there is mass entering the domain.

[Weiqiang Liu]

Originally Posted by LuckyTran

Then you have a surface flux, not a volumetric source. Surface fluxes don't go in the governing equations, they go in the boundary conditions.


For example: in a velocity inlet, there is no mass source even though there is mass entering the domain.

so I don't have to define mass source term?