Relationship between specific heat capacity and enthalpy

By definition, the specific heat capacity is the derivative of the enthalpy with respect to temperature at constant pressure. Therefore, we can use any correlation that we use to calculate enthalpy to calculate the specific heat capacity. That is, we take the derivative of the enthalpy correlation to give us the correlation for specific heat capacity.

To provide more intuitive thermodynamic specifications, AVEVA Process Simulation shows correlations and coefficients for specific heat capacity instead of enthalpy. Internally, AVEVA Process Simulation still uses the integrated (enthalpy) form of the equation and sets the constant of integration to zero, while AVEVA Thermodynamic Data Manager (TDM) always uses the integrated form for calculations. Therefore, in TDM, you see the coefficients for the integrated form (Ci). However, in AVEVA Process Simulation, you see and specify the coefficients for the derivative form (Di).

Setting the constant of integration for the enthalpy form (typically C1) to zero allows us to cancel out that term when calculating enthalpy, so that we can accurately map the integrated and derivative coefficients to get matching calculation results in both AVEVA Process Simulation and TDM.

Depending on the correlation, there may not be a one-to-one mapping between the integrated and derivative coefficients (Di = Ci+1 or Di = Ci). If you often view and update thermodynamic data in TDM or are trying to transform existing enthalpy data into specific heat capacity data, you should review the coefficient mapping for the correlation to determine how your changes to an enthalpy correlation coefficient affect the corresponding coefficient for the specific heat capacity in AVEVA Process Simulation. See Equation forms for temperature-dependent properties in AVEVA Thermodynamic Data Manager for more details on the correlations.