Tea: different behavior when computing properties together

[seb007]

[jasper]

[seb007]

Thanks for these very useful comments. I fixed the BSTR issues (by always using CComBSTR), and called Initialize and Terminate functions.

I do not use smart pointers for COM objects, but normal pointers initialized to NULL in the class constructor and released in the destructor, because they are class members declared in a .h file in which I do not want to include any COM stuff.

I agree that the difference can result from the solver tolerance. Note that the relative error can be as high as 1e-4 for certain values of p and T:

Computing internal energy and its derivatives:
T 2.704082e+002 p 6.816327e+006 U -2.533797e+005

Computing only internal energy:
T 2.704082e+002 p 6.816327e+006 U -2.534055e+005

[jasper]

[jasper]

Note that Terminate and Release must be done on 'primary PMC objects'. These are the ones you create (e.g. with CoCreateInstance), but also the ones that are created from a 'factory' object. Particularly property packages created by thermo systems or property package managers. Derived objects (parameters and ports of unit operations for example) do not need to be initialized and terminated.

[seb007]

It looks like the error on TEST3 has been fixed after I made the changes you proposed.

I played with TEA properties: it is not the Newton tolerance, but the value of the temperature and pressure perturbation, used to compute derivatives I suppose.

The strange thing is that I can set them to 1e-14 and get machine precision match between tests 1 and 2. I expected a value of about 1e-7 to be optimal.

[jasper]

The perturbation is used for enthalpy in case the approx enthalpy derivative model is not selected. The analytic derivatives for enthalpy require first order derivatives of (d ln Phi / d T) or (d ln gamma / d T) with respect to T, P and X, so second order derivatives of ln Phi and ln gamma. I have implementations that provide this, but not in TEA; TEA does these by perturbation. Internal energy is calculated from enthalpy, volume and pressure.

This should not affect the precision of the internal energy value itself though - merely its derivatives.

[seb007]

[seb007]

[jasper]

You are correct that there was a book-keeping problem there (in volume values, when volume is evaluated from the EOS calculation routine in combination with a perturbation, e.g. enthalpy.Dpressure, such as is done by the internal energy routine). Corrected, and the correction is available via CUP. Thank you for reporting this issue.