# UDS source term units

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 July 8, 2002, 06:30 UDS source term units #1 Ale Guest   Posts: n/a Hi to all, which are the units of the source terms for user defined scalar in fluent? If I write a source term for a scalar, e.g. a concentration (kmol/m^3), using mass flow rate as the flux function, the solved equation should be eq. 9.2-3 on page 9-2 of Fluent6 UDF Manual. According to this equation the units should be kg*m^-3*s^-1*(scalar unit), i.e. for concentration, kg*kmol*m^-6*s^-1. Is that right? Should I multiply a source term whose units are kmol*m^-3*s^-1 by the density (or by something else) to fit the units used in Fluent? Is it the same for Fluent4, Fluent5 and Fluent6? Thanks a lot

 July 8, 2002, 15:29 Re: UDS source term units #2 Lanre Guest   Posts: n/a Source term is always defines as source per unit volume. What at the units of a UDS? You define this. So your source units are (UDS stuff)/m^3 rarnaunot likes this.

 July 12, 2002, 13:01 Re: UDS source term units #3 Ola Nordblom Guest   Posts: n/a Hi, It's more convenient to define your scalar concentration per unit mass of mixture instead of per unit volume. Thus, your scalar should have the unit (kmol/kg), and the source term in the scalar transport equation should have the unit kmol/(m^3*s). In fact, since the convective flux in Fluent is a "mass flow rate", the scalar must be expressed per unit mass to get a correct convective transport. Of course, after you have solved your scalar equation, you can multiply your results by the density to get the concentration in (kmol/m^3) if you prefer to present your results using that unit. Regards, Ola Nordblom

March 29, 2017, 07:08
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Rosario Arnau
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Quote:
 Originally Posted by Ola Nordblom ;101704 Hi, (...) Thus, your scalar should have the unit (kmol/kg), and the source term in the scalar transport equation should have the unit kmol/(m^3*s). (...) Ola Nordblom
Hi!!

How can I set the units od my UDS??

I thought that their units are always kg/m^3.....

I need to define the units of my UDS to g/m^3 and kmol/m^3....

Thanks!