# Udf for species concentration (interfacial area udf)

Member Posts: 3

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 */

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 variable in fluent that 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,

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