Incorrect Specific Heat Value when I used a Polynomial or the Kinetic Theory
 

I tried to insert the constant pressure specific heat of water vapour along the saturation curve from the steam table. However, the values computed from Fluent is about 300 J/kg-K higher than values given by the steam table. I switched to the piecewise-liner option and inputted the tabulated values, the same happens.



Moreover, when I used the kinetic theory for specific heat. I used 9 as the degree of freedom for water. However, now, the computed specific is too small and I have to use 12 as the degree of freedom in order to obtain the correct values. Is Fluent counting the degree of freedom the same way as in Physical Chemistry textbook?



Any assistances are appreciated. Thanks.