# Calculation of the molar flow rate

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 July 18, 2012, 08:56 Calculation of the molar flow rate #1 New Member   Join Date: Jul 2012 Posts: 6 Rep Power: 11 Hello everyone ! In my problem I have a cylindrical geometry with an inlet and an outlet with a mixture inside and I want to determinate the molar flow rate in the inlet and the outlet. The formula to calculate the molar flow rate is : Where C is the concentration of the specie, V the velocity of the flow and S the surface The Inlet ID is 23, the outlet is 24 and my mixture ID is 15. I've tried to code it but I've several issues : Here's my UDF for my inlet case: #include "udf.h" DEFINE_EXECUTE_AT_END(measure_molar_flow_rate_inl) { Domain *d; real molar_flow_rate_inl=0.; face_t f; Thread *t; d = Get_Domain(15); t= Lookup_Thread(d, 24); begin_f_loop(f,t) { molar_flow_rate_inl+=NV_MAG(A)*F_W(f,t)*"Concentra tion"; /* How to define the face concentration of a specific specie when my mixture contains several species and how I can define A in NV_MAG(A) ???*/ } end_f_loop(f,t) } printf("Molecular Flow Rate inlet: %g\n",molar_flow_rate_inl); Thank you for your future answers !!!

 July 19, 2012, 04:52 #2 New Member   Join Date: Jul 2012 Posts: 6 Rep Power: 11 I have a litlle bit improved my code : #include"udf.h" #define i_ch4 1 #define i_h2 2 #define mw_ch4 16.04303 #define mw_h2 2.01594 DEFINE_ON_DEMAND(efficiency) { real A[ND_ND]; real molar_inlet=0; real molar_outlet=0; real efficiency=0; int inlet_ID=23; int outlet_ID=24; Domain *d=Get_Domain(1); Thread *t_inlet=Lookup_Thread(d,inlet_ID); Thread *t_outlet=Lookup_Thread(d,outlet_ID); face_t f; begin_f_loop(f,t_inlet) { F_AREA(A,f,t_inlet); molar_inlet += F_FLUX(f,t_inlet)*F_YI(f,t_inlet,i_ch4)/(mw_ch4)*1e-3; } end_f_loop(f,t_inlet); Message("inlet %f mol/s of CH4\n",molar_inlet); begin_f_loop(f,t_outlet) { F_AREA(A,f,t_outlet); molar_outlet += F_FLUX(f,t_outlet)*F_YI(f,t_outlet,i_h2)/(mw_h2)*1e-3; } end_f_loop(f,t_outlet); Message("outlet %f mol/s of H2\n",molar_outlet); efficiency=molar_outlet/(2*molar_inlet); Message("Efficiency %f %\n",efficiency); } It is compiled under Fluent but it returns 0 for each case while there is a mass rate of CH4 and H2 at the boundaries. At the end of calculation it is stated :" Unable to enter text edit mode " maybe it is the error ? I don't understand why it doesn't work, if someone could help me. Last edited by sylvix48; July 19, 2012 at 06:04.

July 19, 2012, 05:15
#3
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Alex
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Quote:
 Message("Efficiency %f %\n",efficiency);
Are you sure that the second % isn't misunderstood by the compiler?

 July 19, 2012, 05:34 #4 New Member   Join Date: Jul 2012 Posts: 6 Rep Power: 11 No it's not that. I've tried without it still doesn't work. Moreover it is already 0 for the inlet and the outlet. I don't get also why it is printed several time on my screen when I ask to write it once ?