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December 10, 2012, 02:20 
UDF for Temperature Dependent Energy Source

#1 
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Mukesh
Join Date: Sep 2012
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Hello All,
I am solving a problem wherein there is an energy source term with two parts: 1) Part dependent on Temperature [i.e. T*(Cp_g  Cp_s) ] 2) Part independent of Temperature Can anybody suggest how to include temperature dependent source term in the UDF as we know Energy equation solves for Temperature. Thanks a lot Mukesh 

January 11, 2013, 05:28 

#2 
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Hi Mukesh,
did you get any response or help in this please? i'm also having the same problem. i was thinking using DEFINE_SOURCE and C_T macro, but not yet sure how to relate them.
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Thank you for your kind attention. Kind regards, mactech001 Currently using: ANSYS v13 

January 18, 2013, 05:32 
problem on UDF returned parameters

#3 
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Dear all,
i've the following UDF code that attempts to apply a temperaturedependent source term to a solid cell. #include "udf.h" #include "mem.h" DEFINE_SOURCE(cell_x_source,cell,thread,dS,eqn) { real source; int Ro=12e3; /*12mOhm at 20C*/ int To=20; /*temperature 20C*/ int Iphase=20; /*Arms*/ source=Iphase*Iphase*Ro*((C_T(cell,thread)273)/To)/C_VOLUME(cell,thread); Message("C_T output: %g\n",C_T(cell,thread)); Message("source output: %g\n",source); Message("C_VOLUME output: %g\n",C_VOLUME(cell,thread)); return source; } While running 100 iterations, i observe in the Message output that the C_VOLUME of the solid cell is changing rather than keeping at a constant value as expected. why is this happening please? The final outcome of the run was: Error: Divergence detected in AMG solver: temperature Error Object: #f Hope to receive any comments/ideas you may have.
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Thank you for your kind attention. Kind regards, mactech001 Currently using: ANSYS v13 

January 18, 2013, 10:49 

#4 
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Mukesh
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Hello,
Though I'm not sure if we could use the MACRO C_T(c,t) for SOURCE term in Energy equation, still I suggest you remove that C_VOLUME(c,t) as we must define source term as per unit volume to correctly solve the Energy eqn in FLUENT. Hope that works. All The Best, Mukesh 

January 18, 2013, 11:56 

#5 
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Dear Mukesh,
thank you for your response. The C_VOLUME in my equation is to obtain the volume of the solid cell, and use it to divide my energy/power in order to express the source in per volume. Note that in the source equation, i've divided by C_VOLUME. My only query is: Why the C_VOLUME value is changing from one iteration to the next?
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Thank you for your kind attention. Kind regards, mactech001 Currently using: ANSYS v13 

January 19, 2013, 06:07 

#6  
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Mukesh
Join Date: Sep 2012
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Could you please send in your energy equation so as to check the units. FLUENT solves equations with source in Unit/volume terms only. So please check the units.
Best of Luck......Mukesh Quote:


January 19, 2013, 09:31 

#7 
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Dear Mukesh,
In my application, my source term: source=Iphase*Iphase*Ro*((C_T(cell,thread)273)/To)/C_VOLUME(cell,thread); where, Iphase*Iphase*Ro*((C_T(cell,thread)273)/To) is in units of Watts C_VOLUME(cell,thread) is in units of cubic meters;
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Thank you for your kind attention. Kind regards, mactech001 Currently using: ANSYS v13 

September 15, 2017, 10:27 

#8 
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maziyar ghanikolahloo
Join Date: Jan 2017
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Dear machtech001,
I want to write a UDF in which there is a constant term and also a negative term which is related to temperature. I am new to UDF how can I accomplish that? I want to use Average Temp of the solid zone and source term should be used just in solid zone. #include "udf.h" DEFINE_SOURCE(source_term,cell,thread,dS,eqn) { real source; real temp=C_T(cell,thread); int a=0.5546; int b=1.84*10^4; int I=700; int SCR=1000; int A=373.83; source=261682243(a*(1b)*temp)*I*SCR*A return source } 

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