# UDF unit and FLUENT output

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 September 14, 2010, 22:52 UDF unit and FLUENT output #1 New Member   ALAM Join Date: Sep 2010 Posts: 7 Rep Power: 9 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 Last edited by saifulraju; September 22, 2010 at 06:58.

 September 15, 2010, 02:31 #2 Member   Byron Smith R J Join Date: Mar 2009 Location: India Posts: 46 Rep Power: 10 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

 September 15, 2010, 11:52 #3 New Member   ALAM Join Date: Sep 2010 Posts: 7 Rep Power: 9 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?

 September 16, 2010, 00:35 #4 Member   Byron Smith R J Join Date: Mar 2009 Location: India Posts: 46 Rep Power: 10 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 Jianqi Shen likes this.

 September 21, 2010, 22:22 time vs rate of reaction #5 New Member   ALAM Join Date: Sep 2010 Posts: 7 Rep Power: 9 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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