[gauravkmr]

Hi all,
I am modelling the supercritical fluids and as the thermophysical properties changes abruptly, I need to write the UDF for the specific heat of the water. I have fitted the curve in a piecewise manner as follows
200 <= T < 385
C_p=(10.57678-0.02301T)/(1+0.00537T-2.05557×〖10〗^(-5) T^2 )

385 <= T < 600
C_p=(0.83318-0.0033T)/(1-0.00319T-1.49076×〖10〗^(-6) T^2 )

Please help me to write the UDF for the same. Parallelize the code if needed as I am using 20 cores processor
Thanks

[pakk]

Of course we can help you to make this UDF!

Step 1: find a similar UDF in the Fluent Manual.
Step 2: change it so that you think it does what you want.
Step 3: compile it, check for errors.
Step 4: fix errors until it compiles.
Step 5: check if the UDF does what you want.

Which step is giving you problems?

[AlexanderZ]

specific heat can be defined through material properties, you don;t need UDF for that

[gauravkmr]

I have written the code as you suggested, here is my code:
#include "udf.h"
DEFINE_SPECIFIC_HEAT(my_user_cp, T, Tref, h, yi)
{
real cp;
if (200 <= T < 385)
cp = 10.57678-0.02301*T/(1+0.00537*T-2.05557*pow(10,-5)*pow(T,2));
else
cp = 0.83318-0.0033*T/(1-0.00319*T-1.49076*pow(10,-6)*pow(T,2));
*h = cp*(T-Tref);
return cp;
}

But when I check the value of Cp after running the program in C, the value for 385 <= T <600 is not correct while it is correct for other ranges what is wrong please check it.
Thanks and Regards.

[pakk]

if (200 <= T < 385)

This does not do what you expect it does. Split it in two :

if ((200 <= T) && (T< 385))

[gauravkmr]

Thanks, Pakk it works.