[erginbayrak]

Hi, I have been trying to import the thermophysical properties of CO2 (for the supercritical region) to Fluent by using UDF. End of the analysis, the result is not correct. I think Fluent is pulling a Tref value which causes my enthalpy to go negative; therefore, the energy equation does not give accurate temperature results, so the result of thermophysical properties, which are functions of temperature, are wrong. I want to be grateful if you could share your recommendations, especially on the methods of correct calculation of enthalpy. My specific heat code is as follows:
#include "udf.h"
DEFINE_SPECIFIC_HEAT(supercritical_cp, T, Tref, h, yi)
{
real cp;
if (300. >= T)
{
cp = 2.256999118844760E-02 * pow(T, 4.) - 2.606618818487370E+01 * pow(T, 3.) + 1.129129898467780E+04 * pow(T, 2.) - 2.174235523392760E+06 * T + 1.570278261279480E+08;
}
if (300. > T >= 306.)
{
cp = 1.147018354719330E+01 * pow(T, 4.) - 1.385519872072390E+04 * pow(T, 3.) + 6.276090044658930E+06 * pow(T, 2.) - 1.263530241490370E+09 * T + 9.539285116131690E+10;
}
if (306. > T >= 307.8)
{
cp = -1.611612838918710E+04 * pow(T, 4.) + 1.978085636985280E+07 * pow(T, 3.) - 9.104578256081260E+09 * pow(T, 2.) + 1.862478067464320E+12 * T - 1.428738938943020E+14;
}
if (307.8 > T >= 310.)
{
cp = -1.576135476848110E+03 * pow(T, 4.) + 1.945866130859760E+06 * pow(T, 3.) - 9.008641337104630E+08 * pow(T, 2.) + 1.853611584329810E+11 * T - 1.430227164258690E+13;
}
if (310. > T >= 320.)
{
cp = 1.770529718817220E+00 * pow(T, 4.) - 2.242833202341920E+03 * pow(T, 3.) + 1.065432793165650E+06 * pow(T, 2.) - 2.249454519629040E+08 * T + 1.781003821884030E+10;
}
if (320. > T)
{
cp = 2.086961941877520E-03 * pow(T, 4.) - 2.851496372954040E+00 * pow(T, 3.) + 1.461548345109060E+03 * pow(T, 2.) - 3.330816449664890E+05 * T + 2.848088978782360E+07;
}
*h = cp*(T-Tref);
return cp;
}