[Tleja]

Hi everyone,

At the moment, I need to use user defined-scalar (UDS) to solve concentration balance by defining scalar as molar concentration (kmol/m^3).

I will write a source term for a user defined-scalar(concentration (kmol/m^3)), using mass flow rate as the flux function as the equation below:



According to this equation the units of each term should be kg/m^3 s*(scalar unit), Thus, the source term of molar concentration unit is kg*kmol/m^6 s. Is that right?
I'm not sure about my understanding.

Which is the units of the source terms for user defined scalar in fluent?

Can I multiply a source term whose units are kmol*m^-3*s^-1 by the density to fit the units used in Fluent?

Thanks a lot

Tleja

[Bruno Machado]

Originally Posted by Tleja

Hi everyone,

At the moment, I need to use user defined-scalar (UDS) to solve concentration balance by defining scalar as molar concentration (kmol/m^3).

I will write a source term for a user defined-scalar(concentration (kmol/m^3)), using mass flow rate as the flux function as the equation below:



According to this equation the units of each term should be kg/m^3 s*(scalar unit), Thus, the source term of molar concentration unit is kg*kmol/m^6 s. Is that right?
I'm not sure about my understanding.

Which is the units of the source terms for user defined scalar in fluent?

Can I multiply a source term whose units are kmol*m^-3*s^-1 by the density to fit the units used in Fluent?

Thanks a lot

Tleja

it is a volumetric source term. so it is [WHATEVER THE UNIT]/m3.s

[Tleja]

Hi Bruno

Thank you for your reply

Actually, my system is multi-phases system (gas-solid). I think i can not solve UDS transport equation by directly adding volumetric source term as you mentioned.

As my understanding, my user-defined scalar should be solved according to equation 1.3-5 in the link of http://www.afs.enea.it/project/neptu.../th/node14.htm

Thus, UDS unit in each term should be consistent with each other for solving the other transports equation.

I have derived the unit of each term. I found that if i want to solve UDS in the unit of kmol/m(s)^3, the unit of each term should be kg/m^3 s*(kmol/m(s)^3).

***m(s)^3 = volume of solid phase (this unit can make a consistence by multipying volume fraction of solid phase)***

Nevertheless, I'm not sure that it is possible to solve UDS in the unit of kmol/m(s)^3 ??????

Best regard
Tleja

[Bruno Machado]

Originally Posted by Tleja

Hi Bruno

Thank you for your reply

Actually, my system is multi-phases system (gas-solid). I think i can not solve UDS transport equation by directly adding volumetric source term as you mentioned.

As my understanding, my user-defined scalar should be solved according to equation 1.3-5 in the link of http://www.afs.enea.it/project/neptu.../th/node14.htm

Thus, UDS unit in each term should be consistent with each other for solving the other transports equation.

I have derived the unit of each term. I found that if i want to solve UDS in the unit of kmol/m(s)^3, the unit of each term should be kg/m^3 s*(kmol/m(s)^3).

***m(s)^3 = volume of solid phase (this unit can make a consistence by multipying volume fraction of solid phase)***

Nevertheless, I'm not sure that it is possible to solve UDS in the unit of kmol/m(s)^3 ??????

Best regard
Tleja

Your source terms have to be consistent, but not necessarily the same unit. You might have a equation that is kg/m3.s and another one that is kmol/m3.s.

To make my example clear, imagine you have one equation for water vapor that its source term unit is kg/m3.s and you have one for liquid water which is in kg/m3.s.

Imagine you have one equation called FUNCTION (kg/m3.s), when creating your source terms, you need to do something like this

Source for gas = FUNCTION (kg/m3.s)

Source for liquid = FUNCTION/MOLECULAR_WEIGHT (kg/m3.s * kmol/kg -> kmol/m3.s)

[Tleja]

Your source terms have to be consistent, but not necessarily the same unit. You might have a equation that is kg/m3.s and another one that is kmol/m3.s.

To make my example clear, imagine you have one equation for water vapor that its source term unit is kg/m3.s and you have one for liquid water which is in kg/m3.s.

Imagine you have one equation called FUNCTION (kg/m3.s), when creating your source terms, you need to do something like this

Source for gas = FUNCTION (kg/m3.s)

Source for liquid = FUNCTION/MOLECULAR_WEIGHT (kg/m3.s * kmol/kg -> kmol/m3.s)

Hi Bruno

Thank you so much for giving me good information

As you mentioned about source for liquid, you mean that the unit of my scalar (UDS) should be kmol/kg. Is it right??

Unfortunately, the specie in my system can not be defined in term of certain molecular weight because this specie is polymer. Nevertheless, i know only amount of polymer in term of molar concentration (kmol/m3).

Do you have any idea to calculate UDS transport equation for molar concentration (kmol/m3)?

Best Regard

Tleja

[Bruno Machado]

Originally Posted by Tleja

Hi Bruno

Thank you so much for giving me good information

As you mentioned about source for liquid, you mean that the unit of my scalar (UDS) should be kmol/kg. Is it right??

Unfortunately, the specie in my system can not be defined in term of certain molecular weight because this specie is polymer. Nevertheless, i know only amount of polymer in term of molar concentration (kmol/m3).

Do you have any idea to calculate UDS transport equation for molar concentration (kmol/m3)?

Best Regard

Tleja

No, what I meant is that you will be taking something from one equation (gas) and adding in another (liq), but this has to respect the unit conversion.

Considering volume which is an easy unit, if you take 1m3 from one equation, you can add in a different equation as 1000 liters. You have 2 different equations, with 2 different units, but what you have taken from one, was converted to a different unit and was added into the second.

[rarnaunot]

Hello everyone!

I have almost the same problem: I want to define a UDS in g/m3 and the corresponding Source term in g/(m3s). To avoid the unit problems I have passed all to kg so my UDS is in kg/m3 and the source term in kg/(m3s)...but it didn't work fine.

Can I change the UDS units somewhere?

How do you "say" to Fluent that your units are g/m3 or kmol/m3?? (If I didn't missunderstand u, the default units are kg/m3)

[Tleja]

Hi Rarnaunot

In my understanding, your UDS unit can be whatever you want.

But, you have to make sure the unit of each term in UDS transports equation is the same.

Please take a look at equation 9.3-1 or 9.3-5
https://www.sharcnet.ca/Software/Flu...ug/node385.htm

The unit for all terms have to be the same (kg/m3s)(UDS unit).

if i miss understanding, Please let me know

Best Regard
Tleja