Hi Chris,

The origin of the problem is in the setState_pTX function. In OpenModelica the information message is telling that there are duplicate elements not identical. You are extending the original function and you are redeclaring the input and output variables. If you redeclare the function without extension, or you take out the redeclaration of variables, the problem is solved. For example:
  redeclare function extends setState_pTX "Return thermodynamic state as function of p, T and composition X or Xi" extends Modelica.Icons.Function;
    algorithm
      state := ThermodynamicState(p = p, T = T, X = X);
    annotation(
      Inline = true);
  end setState_pTX;

It is strange that if you change the test to PartialTestModel2, that is an extension of the one you are using, there is no problem with your original code. I would think that there is no problem with your code, but with the tool.

Carlos

Hi Carlos!
Thanks a lot for your reply. I revised the use of extend but unfortunately this didn't resolve the problem.
But in another forum Stack overflow - Two-phase Modelica example I found an interesting example of how to set up a new medium Water - temperature dependent density. Looking at the example I noticed that I was missing at least some XXX_reference and default_XXX values and probably even more important in the different functions it should be indicated how often they may be differentiated, using something like annotation(..., smoothOrder=N, ...). Not doing so results in an error stating I have a singular matrix.
In summary using the stated example I was able to set up a medium that passes the tests. I am leaving this reply here in case someone else faces the same problem.
Cheers
Christian

Hi Christian,

Thank you very much for the information. In fact I didn't take enough care. With the solution I proposed the model compiles and runs on OpenModelica 1.14.1 on Windows, but I didn't look at the Simulation Output window, it is telling that after a successful initialization the simulation terminated by an assert at time 0.00038.
This is different from what you are experiencing. Normally after initial convergence you have no problems. I have written several media packages, and what you tell is completely right: having good reference and default values for pressure, temperature and enthalpy is of great importance for convergence. I normally do not specify smoothOrder, but I know it is a help for the solver.

Regards

Carlos

Hi Carlos!
In some configuration I had seen this error as well. This is a little bit off topic, but is there a tutorial / book or any other source giving more insight in these details of modeling fluid systems with OM? Actually I want to do simulations with an absorption chiller but I am struggling quite a lot.
Cheers
Christian

Hi Christian,
As far as I know there is no book that could be a reference for the modeling of media, or mass transfer with Modelica. I found interesting, although now it is quite old, this dissertation from C.C.Richter link.
For me there are three main fields: fluid properties calculation, fluid flow and heat transfer, and mass transfer.
Regarding properties calculation, the Media library from the Modelica standard library is quite adequate, although there are not models for multicomponent, multiphase, mediums. The examples that come with the library, mainly for water and air are good, but quite complex. When you want to work with other fluids you do not find too much to choose, at least open source. There is the External Media library, that allows to link with CoolProp or ReefProp, but as far as I know it is almost impossible to make it work with Open Modelica. There is also the system library HelmholtzMedia, but it is not easy to extend an it is also not working. So I decided to make my own libraries, that you can find here. The more flexible one is using external functions and objects and therefore is not supported by the new frontend of Open Modelica (necessary to wait for its implementation in version 2.0), but yes by the old frontend.
Regarding fluid flow and heat transfer, I think that the Fluid library implemented in Modelica is too complex to be useful, and I see that there is much more people sharing this oppinion. I come from the engineering field where "keep it simple" is a must. I am polishing the library that I have used along some years in order to publish it as open source.
Regarding mass transfer, I understand that the first necessary step is to have a multicomponent, multiphase media definition, but there is nothing here for now. Work for the future.

Cheers

Carlos

Hi Carlos!
Thanks for the advice I could take a look at the thesis. As I am engineer as well, in my opinion KISS is always a good strategy. Actually I could set up my medium to run with the tests provided and took some steps further to build an absorption cooling system. But I ran into more difficulties. At first I built two separate modules one for the Absorber / Evaporator and one for the Generator / Condenser. The modules compiled fine but joining them with some expansion valve and pump resulted in an error I could not solve yet. Therefore I put some of the parts together into a small test module and I the following problem:
The code posted here runs fine unless uncomment the two commented blocks including the lines starting with Abs_.... . Doing so results in this error: "Error in region computation of IF97 steam tables(p = 5582.09, T = 308)". Do you have any suggestions?
I attached the file as well and the file including the medium definition I use (LiBrH2O_5). Both are undocumented but I hope easy to understand
Cheers Christian

model H2OTest

  replaceable package Refrigerant = Modelica.Media.Water.WaterIF97_pT;

  replaceable package Solution = LiBrH2O_5;

  

  // Generator parameters

  Refrigerant Gen_H2O;

  Modelica.Media.Interfaces.Types.SaturationProperties Gen_H2OSat;

  Refrigerant.ThermodynamicState Gen_H2O_liq;

  // dew point, one-phase side

  Refrigerant.ThermodynamicState Gen_H2O_vap;

  

  Solution.ThermodynamicState Gen_state;

  Modelica.SIunits.SpecificEnthalpy Gen_h_sol(start=1.0e5);

  Modelica.SIunits.SpecificEnthalpy Gen_h_dot_eva(start=1.0e5);

  Modelica.SIunits.SpecificHeatCapacity Gen_cp_sol(start = 4.2e3);    

  

  Modelica.SIunits.Mass Gen_M_g(start = 20, min = 0);

  Modelica.SIunits.Mass Gen_M_c(start = 20, min = 0);

  Modelica.SIunits.Mass Gen_M_v(min = 0);



  Modelica.SIunits.MassFlowRate Gen_m_dot_con(start = 0, min = 0);

  Modelica.SIunits.MassFlowRate Gen_m_dot_eva(start = 0, min = 0); 

  

  Modelica.SIunits.Temp_K Gen_T_g(min = 273.15, max = 373.15, start = 298);

  Modelica.SIunits.Temp_K Gen_T_c(min = 273.15, max = 373.15, start = 308);   

  

//  Refrigerant Abs_H2O;

//  Modelica.Media.Interfaces.Types.SaturationProperties Abs_H2OSat;

//  Refrigerant.ThermodynamicState Abs_H2O_liq;

//  Refrigerant.ThermodynamicState Abs_H2O_vap;  



equation

  Gen_H2OSat = Gen_H2O.setSat_T(Gen_T_c);

  Gen_H2O_liq = Gen_H2O.setBubbleState(Gen_H2OSat);

  Gen_H2O_vap = Gen_H2O.setDewState(Gen_H2OSat);

  

  Gen_state = Solution.setState_pTX(Gen_H2OSat.psat, Gen_T_g, {0.5, 0.5});

  Gen_cp_sol = Solution.specificHeatCapacityCp(Gen_state);

  Gen_h_sol = Solution.specificEnthalpy(Gen_state);

  Gen_h_dot_eva = Gen_H2O_vap.h - Gen_h_sol;



  der(Gen_M_c) = Gen_m_dot_con;

  Gen_M_c * Gen_H2O.specificHeatCapacityCp(Gen_H2O_liq) * der(Gen_T_c) = Gen_m_dot_con * Gen_H2O_liq.h;  

  der(Gen_M_g) = Gen_m_dot_eva;

  0 = Gen_m_dot_eva * Gen_h_dot_eva + Gen_M_g * Gen_cp_sol * der(Gen_T_g);  

  der(Gen_M_v) = (-Gen_m_dot_con) + Gen_m_dot_eva;

  0 = Gen_m_dot_con * abs(Gen_H2O_vap.h - Gen_H2O_liq.h) + Gen_m_dot_eva * Gen_H2O_vap.h + Gen_H2O.specificHeatCapacityCp(Gen_H2O_vap) * der(Gen_T_c) * Gen_M_v;    

  Gen_T_g = Solution.saturationTemperature(Gen_state);

  

//  Abs_H2OSat = Abs_H2O.setSat_T(283);

//  Abs_H2O_liq = Abs_H2O.setBubbleState(Abs_H2OSat);

//  Abs_H2O_vap = Abs_H2O.setDewState(Abs_H2OSat);



end H2OTest;

LiBrH2O-5.mo

H2OTest.mo

Hi Chris,

It seems an OpenModelica fault. I received no error message, but I am using the old frontend by default. When I switched to the new frontend the message appeared. The selected medium should be able to calculate the saturation states at 283 K,  nevertheless I changed the medium to StandardWater, that in fact is WaterIF97_ph, and the problem disappeared also with the new frontend.
Just one question, Why do you make two copies of the Refrigerant package (Gen_H2O and Abs_H2O) instead of using it directly. It seems also better to use Refrigerant.SaturationProperties instead of Modelica.Media.Interfaces.Types.SaturationProperties.
Regarding your media definition, I have not had enough time to review it, but I will try to do it in the next days.

Regards

Carlos

Hi Carlos!
Thanks a lot for your reply, you are the light in the tunnel!

> Why do you make two copies of the Refrigerant package (Gen_H2O and Abs_H2O) instead of using it directly.

Actually I want to have these in separate modules but as I was not able to get them running I decided to join the stuff in one module first, get it running and separate again later on. Therefore I maintained the final variable structure

> It seems also better to use Refrigerant.SaturationProperties instead of Modelica.Media.Interfaces.Types.SaturationProperties.

I simply was not aware of this member, thanks for the advice, already changed it!

Cheers Christian