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-   -   UDF unit and FLUENT output (http://www.cfd-online.com/Forums/fluent/80088-udf-unit-fluent-output.html)

 saifulraju September 14, 2010 22:52

UDF unit and FLUENT output

Hello,
I am using UDF for particle reaction rate. But the difficulty is the consistence of unit. In my UDF(given below) equation the unit is per second. But the FLUENT gives the unit kgmol/m2-s after convergence. Could you please tell how can I get the same unit in FLUENT solution. Is it possile to plot rate of reaction versus time?

/* UDF of specifying the surface reaction rate of a particle */
#include "udf.h"
#define A3 1.36e6
#define E3 1.38e8
#define n3 0.68
#define shi 2.0

DEFINE_PR_RATE(user_pr_rate,c,t,r,mw,pp,p,sf,dif_i ,cat_i,rr)
{
real ash_mass = P_INIT_MASS(p)*(1.-DPM_CHAR_FRACTION(p)-DPM_VOLATILE_FRACTION(p));
real one_minus_conv = MAX(0.,(P_MASS(p) -ash_mass) / P_INIT_MASS(p)/ DPM_CHAR_FRACTION(p));
if (!strcmp(r->name, "reaction-3"))
{
real kp3 = A3*exp(-E3/UNIVERSAL_GAS_CONSTANT/P_T(p));
real kd3 = 2.303*log(one_minus_conv);
real ke3 = sqrt(1-shi*kd3);
*rr=-kp3*one_minus_conv*ke3;
}
}

With thanks,
Alam

 byronsmith September 15, 2010 02:31

hai
The rate of surface reaction should be fed in kmol/m2 s only. whatever you give through ur udf will be computed and expressed by fluent in its unit only. so convert the unit kg/s into kmol/m2 s in hte udf and try the solution

 saifulraju September 15, 2010 11:52

Hi,
Thank you. But if the rate of reaction has the unit (per second), it is not possible to convert in kgmol/m2-s.
So what will I do in this case?

 byronsmith September 16, 2010 00:35

hai
you can manupulate the unit 1/s by multiplying the rate obtained by density, divide by surface area per unit volume and molecular weight (1/s x kg/m3 xm3/m2 x kmol/kg = kmol/m2 s. hope this helps

 saifulraju September 21, 2010 22:22

time vs rate of reaction

Dear Byron Smith R J,
Thanks. I got the point.
Could you please tell me how can I get the numerical data for plotting time versus rate of reaction.

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