I am trying to calculate the change in enthalpy and entropy for a heat transfer fluid (HTF) for modeling purposes. I have one pressure-enthalpy diagram or chart for the HTF and I am also using software 'EES' for the calculation of change in enthalpy and entropy.
For the chart, the reference state at 0 C saturated liquid is: h=43 kJ/kg and s=0.175 kJ/kg.K.
For the software, the reference state at 0 C saturated liquid is: h=200 kJ/kg and s=1 kJ/kg.K.
When I calculate the change in h or s using each method (i.e. chart and software), I get different results. Is it normal that the change in h or s is different when different reference states are used? Because of this I have two sets of power and efficiency calculations which are different from one another under the same conditions.
Hi, if you calculate the change in enthalpy and entropy according to the reference state, then the answer is yes, using a different reference must yield different results. If you calculate the change between two arbitrary states, then the scaling equation is important.
Hi Petr Lepcio. Thank you for the response. I understand that different reference states will lead to different values of enthalpy and entropy. Now I want to understand for the change in two arbitrary state and the use of scaling equation. For example, in my case, I am calculating the enthalpy change between inlet and outlet of the turbine. The difference between enthalpies at inlet and outlet of the turbine calculated from thermodynamic chart and 'EES' is not the same. How must I incorporate the scaling equation in this case to match my results from each method? Thanks again.
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