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Hi!
Thanks for the replies. From other tools (E+) I am used to worry about warning but in case I think it is not a problem they appear. Maybe someone can still comment on the warning concerning the concentration.
Cheers
Christian
Hi!
I a created a LiBr-H2O mixture medium to use in absorption cycles. When doing some basic test with the medium I get some errors I do not know how to deal with. The test is pretty simple, it is two closed vessels connected by a pump and valve forming a closed circuit. When running the simulation I get these errors:
The following assertion has been violated at time 0.000000
valveLinear.port_a_T >= 1.0 and valveLinear.port_a_T <= 10000.0
Variable violating min/max constraint: 1.0 <= valveLinear.port_a_T <= 10000.0, has value: 2.9203e-316
and
The following assertion has been violated at time 0.400000
valveLinear.state_a.X[2] >= 0.0 and valveLinear.state_a.X[2] <= 1.0
Variable violating min/max constraint: 0.0 <= valveLinear.state_a.X[2] <= 1.0, has value: -500
The simulation terminates though and the result seems to be reasonable. Maybe something is not properly initialized? I am using OpenModelica 1.16.1 as the newer version had issues with the connection of components. I would like to understand / solve these errors before moving to more complex scenarios. The according files are attached.
Cheers
Christian
ClosedVessel.mo
Two-Vessels-Pump-Valve.mo
LiBrH2O-5.mo
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
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
Code:
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;
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 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!
As said, I am a newbie to Modelica and having a hard time to create a new medium. My final goal is to create a new mixture medium but as I did not succeed I stepped back and tried to create a new single phase, single component medium but also this does not work out.
Actually creating the medium in terms of syntax seems ok and the model check does not report any errors, but testing the medium with the Modelica.Media.Utilities.PartialTestModel fails. The problem appears, when using a non-constant density. In the code of the model below I tried different things. Once with a constant density declared in the baseProperties which seems to work, once with the density calculated within the baseProperties causing problems and once calling the density function, not working either, though the latter two options give different error.
The medium implemented in the code here is simple water, using not very sophisticated approximations, but the values calculated should be meaningful, though.
Can anyone help me getting this fixed? What am I missing?
Big thanks in advance
Chris
Here is the code of my created medium
Code:
package LiBrH2O_3
extends Modelica.Media.Interfaces.PartialMixtureMedium(
final mediumName = "LiBrH2O_3",
// final substanceNames = {"LiBr", "H2O"},
final substanceNames = { mediumName },
final singleState = true,
final reducedX = true,
final fixedX = false,
ThermoStates = Modelica.Media.Interfaces.Choices.IndependentVariables.pTX);
// Temperature(
// min=273,
// max=450,
// start=293.15),
// T_default = 293.15,
// pressure(
// min = 0,
// max = 1.0e6,
// start = 1.5e5),
// density(
// start = 994),
// SpecificEnthalpy(
// start = 53000
// ),
// SpecificHeatCapacity(
// start = 2300
// ),
redeclare model extends BaseProperties(
final standardOrderComponents = true "Base properties of medium",
h(stateSelect=StateSelect.default),
d(stateSelect=StateSelect.default),
T(stateSelect=StateSelect.prefer),
p(stateSelect=StateSelect.prefer)
)
protected
constant Real ca = 999.79684;
constant Real cb = 0.068317355;
constant Real cc = -0.010740248;
constant Real cd = 0.00082140905;
constant Real ce = -2.3030988e-5;
Real Td = state.T - 273.15;
equation
state = ThermodynamicState(p = p, T = T, X = X);
d = ca + cb * Td + cc * Td^2 + cd * Td^2.5 + ce * Td^3; // fails with some error, running the model test
// d = density(state); // fails with some error when running the medium test
// d = 998; // using constant density here the medium seems to work as epected
h = specificEnthalpy(state);
u = h - p / d;
MM = 0.01801528;
R = 8.3144 / MM;
end BaseProperties;
redeclare replaceable record ThermodynamicState "A selection of variables that uniquely defines the thermodynamic state"
extends Modelica.Icons.Record;
AbsolutePressure p "Absolute pressure of medium";
Temperature T "Temperature of medium";
MassFraction[nX] X(start = reference_X) "Mass fractions (= (component mass)/total mass m_i/m)";
annotation(
Documentation(info = "<html></html>"));
end ThermodynamicState;
redeclare function extends specificEnthalpy "Return specific enthalpy" extends Modelica.Icons.Function;
input ThermodynamicState state "Thermodynamic state record";
output SpecificEnthalpy h "Specific enthalpy";
protected
constant Real d1 = 2.844699e-2;
constant Real d2 = 4.211925;
constant Real d3 = -1.017034e-3;
constant Real d4 = 1.311054e-5;
constant Real d5 = 6.756469e-8;
constant Real d6 = 1.724481e-10;
Real T = state.T - 273.15;
algorithm
h := (d1 + d2 * T + d3 * T^2 + d4 * T^3 + d5 * T^4 + d6 * T^5) * 1000;
annotation(Documentation(info = "<html></html>"));
end specificEnthalpy;
redeclare function extends specificHeatCapacityCp "Return specific heat capacity at constant pressure" extends Modelica.Icons.Function;
input ThermodynamicState state "Thermodynamic state record";
output SpecificHeatCapacity cp
"Specific heat capacity at constant pressure";
protected
constant Real a = 4.2174356;
constant Real b = -0.0056181625;
constant Real c = 0.0012992528;
constant Real d = -0.00011535353;
constant Real e = 4.14964e-6;
Real T = state.T - 273.15;
algorithm
cp := (a + b * T + c * T^1.5 + d * T^2 + e * T^2.5) * 1000;
annotation(Documentation(info = "<html></html>"));
end specificHeatCapacityCp;
redeclare partial function density "Return density"
extends Modelica.Icons.Function;
input ThermodynamicState state "Thermodynamic state record";
output Density d "Density";
protected
constant Real ca = 999.79684;
constant Real cb = 0.068317355;
constant Real cc = -0.010740248;
constant Real cd = 0.00082140905;
constant Real ce = -2.3030988e-5;
Real T = state.T - 273.15;
algorithm
d := ca + cb * T + cc * T^2 + cd * T^2.5 + ce * T^3;
// d := 998;
end density;
redeclare function extends setState_pTX "Return thermodynamic state as function of p, T and composition X or Xi" extends Modelica.Icons.Function;
input AbsolutePressure p "Pressure";
input Temperature T "Temperature";
input MassFraction X[:]=reference_X "Mass fractions";
output ThermodynamicState state "Thermodynamic state record";
algorithm
state := ThermodynamicState(p = p, T = T, X = X);
annotation(
Inline = true);
end setState_pTX;
annotation(
Documentation(info = "<html></html>"));
end LiBrH2O_3;
Code used to test the medium:
Code:
model Test_LiBrH2O
extends Modelica.Media.Examples.Utilities.PartialTestModel(
redeclare package Medium = LiBrH2O_3);
end Test_LiBrH2O;
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