Quick UDS question
If I impose a constant value for a UDS at the inlet then the units are kM/m^3 ?
The UDS diffusivity is the diffusion coefficient* density of the material? Do I input the calculated value? Thanks for the help! 
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UDS diffusivity is equal to (fluid density*diffusion coefficient of scalar in that fluid); this parameter should be set in FLUENT. 
Thank you for your response. I am still slightly confused. When I go to the materials section and open the create/edit materials window. The option says UDS DIffusivity ( kg/ms). When you click edit it says coefficient, which would be m^2/s correct? There are no units listed on that input window.

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Bests, 
OK, So then the scalar would be in kg/m^3 to maintain consistent units?


OK, thank you for the quick response and all the help!

Thank you Amir for all your help. You are actually the one who helped me last suggesting the interpolate function and seem to be the one who knows the most about UDS.
I am trying to replicate this equation as my source term: Conc NO = (Rnomax* Conc.Oxygen)/(Conc. Oxygen + KmeNOS) I am getting numbers with my source code but they do not match up with some previous models. Does this look correct to you? #include "udf.h" /************************************************** **************************************** This UDF calculates Source Terms for the Lumen, Endothelium, Vascular Wall, and Tissue Layer ************************************************** ******************************************/ /*** Species numbers ***/ #define Oxygen 0 #define NO 1 /************************************************** **************************************** Endothelium Source Terms: NO Generation and O2 Consumption ************************************************** ******************************************/ /*** Define Variables for Calculation ***/ #define RNOmax 0.000054; /*Maximum eNOS Production Rate (54 uM/s )>(M/s)*/ #define KmeNOS 4.7; /*MichaelisMenten reaction kinetics term (4.7 Torr)*/ DEFINE_SOURCE( Endothelium_NOGen, c, t, dS, eqn) { real con, concNO; concNO=((RNOmax*C_UDSI(c,t,Oxygen))/(C_UDSI(c,t,Oxygen)+(KmeNOS))); return concNO; } 
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I think there is a problem in your formula! The dimensions are not compatible; e.g., you've added Conc. Oxygen and KmeNOS which have different dimensions and also the whole dimension doesn't reduce to concentration! Maybe there are some unit multiplication factors which have dimension! (Conc. Oxygen + KmeNOS*1); check that. Bests, 
Well it is a partial pressure, Henry's Law, using a MichaelisMeneten reaction source term. So the "concentration" is really a pressure in Torr. I noted it wrong in the code and never fixed it. I really just wanted to know if the coding was correct because and would replicate the equation. I am new to C and this is my first code. Matlab is where the extent of my coding ability lies. Thank you very much for all your help! I truly appreciate it!

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Bests, 
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