[marijam]

Hello,



I am writing 3 different udfs for calculating the concentration of 3 different species of mine. I also have a mass transfer coefficient in another UDF.

I need to use that mass transfer coefficient in one of the concentration UDFs. part of udf is as follows:

OXN = C_YI(c,t,2) * C_R(c,t)+kl*a*(0.08- C_YI(c,t,2) * C_R(c,t)); /*O2 concentration*

I stored kl in a UDM and will replace it in the above line but for a (interfacial area)

So here ''a'' is the interfacial area between gas and liquid. So in case I use a single bubble size in my model I can write the following code for the interfacial area and then store in another UDM and use it in the line mentioned above.



/************************************************** *******************

UDF for specifying interfacial area

************************************************** ********************/

#include "udf.h"



real area_intf;



DEFINE_EXCHANGE_PROPERTY(custom_ia,c,t,i,j)

{



/* i -- liquid-phase; j -- vapor-phase */



Thread **pt = THREAD_SUB_THREADS(t);



real diam = C_PHASE_DIAMETER(c, pt[j]);

real vof_i = C_VOF(c,pt[i]);

real vof_j = C_VOF(c,pt[j]);



area_intf = 6.*vof_j/diam;



C_UDMI(c,t,1)=area_intf;

return area_intf;

}





1- I wanted to make sure if this is correct?, since I get 0 for data stored in C_UDMI(c,t,1).



2- Also I wanted to see if anyone knows how do I define interfacial area when I am using '''''' interfacial area concentration model'''''' with a range of bubbles from 2mm to 1 cm?

3- Is there any specific macro for interfacial area that can read it from fluent and I can directly use (similar to density, viscosity ,...)? Or do I need to find the interfacial area for different bubble categories? (sth similar to PBM) and

3-1- in this case, what is the bubble size macro for the interfacial area concentration model?



Many thanks,

[AlexanderZ]

udf seems to be correct.
UDM could be 0 in two cases:
1. vof_j = 0
2. you didn't hook udf properly, so it is not executed

I can't answer other questions

[marijam]

Originally Posted by AlexanderZ

udf seems to be correct.
UDM could be 0 in two cases:
1. vof_j = 0
2. you didn't hook udf properly, so it is not executed

I can't answer other questions

Thank you for your response. I am using interfacial area concentration in my model and in this case bubble size is not fixed.
Do you happen to know if I should use another Macro for bubble diameter in this case?

Thanks,

[pakk]

Try this :

C_UDMI(c,t,1)=5+area_intf;

Just to see if you still get zero everywhere or not.

[cbooks77]

Hi are you using Fluents species mass transfer model and attaching a kl UDF there or are you developing your own interphase mass transfer model?

I use the species mass transfer alot for bioreactor kLa calculations I usually add my own kL UDF for Higbie Mass transfer/Surface Renewal theory and use the Henrys Law option. I generally start with a monodispersed single bubble size to figure out the average bubble size by tuning it until it matches the experimental volumetric kLa. Then I employ the QMOM PBM. I've never really had any luck with the IAC model and even PBM is very difficult to get a meaningful bubble distribution at times especially without experimental data.