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Hi everyone,
I am new to modelica and got a few issues with a fluid model i created.
I created a moist air System, where locally the rel. hum. rises above 1, so I wanted to create a simple volume, where the in real condensed air can be separated. The model itself and the math works fine, but I have Problems connecting it to the surrounding with fluid ports. The check function says it is underdetermined, but when I am replaceing the fluid port Connection with discrete values, the System works fine. Can someone explain to me which variable from the port I am missing? I already tried the Tracer Connection, but this did not work either. Or if someone knows how to define the problem with standard models, feel free as well .
Here my model:
Code:
model water separator
import Modelica.SIunits.*;
import Modelica.Constants.e;
replaceable package Medium = Modelica.Media.Air.MoistAir;
MassFlowRate m_in;
MassFraction X_steam_in;
MassFlowRate m_out;
MassFlowRate m_liquid;
MassFraction x_sat;
MassFraction X_sat;
parameter Pressure p=1000; //Pa
Pressure p_sat;
EnthalpyFlowRate H_in;
EnthalpyFlowRate H_out;
parameter HeatFlowRate Q=200;
parameter SpecificEnthalpy h_boil=2257000;
Temp_K T(start=288);
Modelica.Fluid.Interfaces.FluidPort_a port_a(redeclare package Medium =
Modelica.Media.Air.MoistAir)
annotation (Placement(transformation(extent={{-10,74},{10,94}})));
Modelica.Fluid.Interfaces.FluidPort_b port_b(redeclare package Medium =
Modelica.Media.Air.MoistAir)
annotation (Placement(transformation(extent={{-10,-94},{10,-74}})));
equation
port_a.p=p;
m_in=port_a.m_flow;
X_steam_in=port_a.Xi_outflow[1];
H_in=port_a.h_outflow*port_a.m_flow;
p_sat=e^(19.016-4064.95/(T-273.15+236.25));
x_sat=0.622*p_sat/(p-p_sat);
X_sat=x_sat/(1+x_sat);
m_liquid=(X_steam_in+X_sat)*m_in;
m_out=m_in-m_liquid;
0=H_in-H_out-Q;
H_out=m_out*(1-X_sat)*Constants.c_p_air*T
+m_out*X_sat*(Constants.c_p_steam*T+h_boil)
+m_liquid*Constants.c_p_water*T;
port_b.p=port_a.p;
port_b.m_flow=m_out;
port_b.Xi_outflow[1]=X_sat;
port_b.h_outflow=H_out/m_out;
port_b.C_outflow = instream(port_a.C_outflow);
annotation (Diagram(coordinateSystem(preserveAspectRatio=false, extent={{-100,
-100},{100,100}})));
end water separator;
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