[soankerabhinay]

I am working on a simulations where specific heat capacity is dependent on temperature. This is the code I used based on fluent manual

#include "udf.h"
DEFINE_SPECIFIC_HEAT(my_user_cp, T, Tref, h, yi)
{
real cp;
if (T<=693)
{
cp = (2.79*T+725.07);
*h = cp*(T-Tref);
return cp;
}
else
{
cp=2729.00;
*h = cp*(T-Tref);
return cp;
}

}

About my transient simulations, basically an heat exchanger where heat transfer fluid is circulated in a pipe, so, as the temperature of the fluid varies with time and space, specific heat needs to be updated using an UDF above. UDF works fine is hooked up (No error messages), but after few hundred seconds, energy residual keeps increasing. If I unload specific heat UDF and keep the specific heat constant then energy residual is stable and residual keeps reducing.
I highly suspect problem is with *h (enthalpy). To begin with, I don't really understand what Tref value I should consider. My simulation starts with the fluid at 365K and I set the T reference value (under reference values) as 365K.
1)Is this correct Tref value?
2) Is *h increase in enthalpy for that time step (If that makes sense), in that case shouldn't DeltaT be (current temperature at node/cell - temperature during previous timestep at that node/cell). My second question may not be accurate, please correct me if it doesn't make any sense.
Any help is greatly appreciated!