UDFSpecific heat as a function of Temperature
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Hi,
I am trying to write a UDF for the Specific heat (Cp) as a function of Temperature. I used "curve fitting" technique to obtain the formula. my First question, am I not sure if I put the below formula correctly (the original one is attached) ? Cp=4.3568+27.57838*exp(0.5*((K19.08514)/2.00369)^2) Second question, why the code is not interrupting ("float" error)? please guide me if through the code is right or not. As its for a transient analysis so, I expected to call the temperature from current temperature. #include "udf.h" DEFINE_SPECIFIC_HEAT(my_user_cp,c,K,thread, position) { real cp; /*specific heat as a function of temperature*/ real K; /* Temperature*/ face_t f; begin_f_loop(f,thread) { F_CENTROID(K,f,thread); Cp = CURRENT_TEMPERATURE; Cp=4.3568+27.57838*exp(0.5*((K19.08514)/2.00369)^2) F_PROFILE(C, K, position) =Cp; } end_f_loop(C,K) } regards, 
As far as I can recall, the binary operator "^" in C means BITAND and it expects both operand to be integer, so you should replace
(...)^2 to pow( (...), 2.0 ) when you need to calculate the power of a float number. Correct me if I am wrong 
Thank you for reply,
Actually, I recived this error for the formula : pow: too few arguments supplied (argument 2) which its : cp=4.3568+27.57838*exp(0.5*(pow((T19.08514)/2.00369),2.0) 
Your ")" does not match "("
cp=4.3568+27.57838*exp(0.5*( pow( (T19.08514)/2.00369,2.0) ) ); 
thank you! the formula's error now solved.
but still have error "invalid type for binary expression: int + pointer to float" it belongs to the line after formula I guess. #include "udf.h" DEFINE_SPECIFIC_HEAT(my_user_cp,c,T,thread, position) { real cp; /*specific heat as a function of temperature*/ real T; /* Temperature*/ face_t f; begin_f_loop(f,thread) { cp=4.3568+27.57838*exp(0.5*( pow( (T19.08514)/2.00369,2.0) ) ); F_CENTROID(T,f,thread); y = CURRENT_TEMPERATURE; F_PROFILE(f, thread, position) =cp; } end_f_loop(C,T) } regards, 
Try this one, adapted from the fluent udf manual.
#include "udf.h" DEFINE_SPECIFIC_HEAT(my_user_cp, T, Tref, h, yi) { real cp=4.3568+27.57838*exp(0.5*( pow( (T19.08514)/2.00369,2.0) ) ); *h = cp*(TTref); return cp; } 
thank you very much,
It was hooked to the Fluent. As I have two UDF file, Is it possible to hook two UDF for analysis at same time ? it seems impossible as I tryied to do! what I should to do ? regards, 
I think at least you can concatenate the two files into a single file.

I did and its work very well. I just paste the second code at the end of first code. let see the results...
many thanks, 
would you please tell me how to change inital temperature value in Fluent ? and in C program code as UDF file ?
as I can see the initial temperature (at step 0) for the model, its 26 C by default by Fluent. how can I change it ? where is the option menu in Fluent ? or in this such a case that in transient analysis I must define at UDF file which its already interrupted to the Fluent ? Note: when I am using hybrid initialization! regards, 
You can use DEFINE_INIT to specify the initial values.

Done!
it works very well, thank you very much, best regards, 
Quote:
Correct equation is integral of cp. 
Quote:

udf for specific heat (cp) of water
Dear friends, I have to write udf for specific heat of water as function of temperature. I have written according to DEFINE_PROPERTY macro, but it is not working. Specific heat of water as a function of temperature (in deg Celsius) is as follows:
cp = 4.2174356  0.0056181625*temp + 0.0012992528*pow(temp,1.5)  0.00011535353*pow(temp,2.0) + 4.14964*pow(10.0,6.0)*pow(temp,2.5) I have seen in UDF manual DEFINE_SPECIFIC_HEAT, but don't understand how can I write for above defined function. Please help me. Thanks in advance:) 
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