Solve nominal temperature differences in heat exchanger convergence issue (#513)

* Added a parameter to introduce default DT for Cp calculation

Signed-off-by: Nabil YOUSSEF <nabil.youssef@metroscope.tech>

* Update CHANGELOG.md

* Improved comments on the default nominal temperatures

Signed-off-by: Nabil YOUSSEF <nabil.youssef@metroscope.tech>

* improved implementation

Signed-off-by: Nabil YOUSSEF <nabil.youssef@metroscope.tech>

---------

Signed-off-by: Nabil YOUSSEF <nabil.youssef@metroscope.tech>

Author: nabily-met

CHANGELOG.md

@@ -12,6 +12,7 @@ Use [gitmoji](https://gitmoji.dev/) to identify your changes.
 ### 🐛 Fixed <!--Make sure to add a link to the PR and issues related to your change-->
 
 ### 💥 Changed <!--Make sure to add a link to the PR and issues related to your change-->
+- Breaking change: added a parameter `nominal_DT_default` to set the nominal temperature differences in heat exchanger to the maximum possible temperature difference [#513](https://github.com/Metroscope-dev/metroscope-modeling-library/pull/513)
 
 ### 🔥 Removed 
 
@@ -45,7 +46,6 @@ Use [gitmoji](https://gitmoji.dev/) to identify your changes.
 
 
 ## MML - v3.8.0
-
 ### ✨ Added <!--Make sure to add a link to the PR and issues related to your change-->
 - Added sensors name in sensors icons [#473](https://github.com/Metroscope-dev/metroscope-modeling-library/pull/473)
 - Added units for volume, surface tension, dynamic viscosity and thermal conductivity [#474](https://github.com/Metroscope-dev/metroscope-modeling-library/pull/474)

MetroscopeModelingLibrary/Examples/CCGT/MetroscopiaCCGT/MetroscopiaCCGT_direct.mo

@@ -133,6 +133,7 @@ model MetroscopiaCCGT_direct
     parameter Real pumpRec_CV_Cvmax = 52.329174; // Recirculation control valve opening
 
   MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Economiser economiser(
+    nominal_DT_default=false,
       QCp_max_side=Eco_QCp_max_side,
     Q_cold_0=56.89394,
     Q_hot_0=510.45065,
@@ -172,6 +173,7 @@ model MetroscopiaCCGT_direct
         origin={56,34})));
   MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Evaporator evaporator(
     x_steam_out(start=1),
+    faulty=false,
     Q_cold_0=47.517586,
     Q_hot_0=510.45065,
     T_cold_in_0=592.94025,
@@ -186,6 +188,7 @@ model MetroscopiaCCGT_direct
     h_0=2691576)
     annotation (Placement(transformation(extent={{-34,28},{-46,40}})));
   MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Superheater HPsuperheater1(
+    nominal_DT_default=false,
       QCp_max_side="unidentified",
     Q_cold_0=47.517586,
     Q_hot_0=510.45065,
@@ -379,6 +382,7 @@ model MetroscopiaCCGT_direct
     T_0=913.15)
     annotation (Placement(transformation(extent={{-370,-7},{-358,5}})));
   MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Superheater Reheater(
+    nominal_DT_default=false,
       QCp_max_side=ReH_QCp_max_side,
     Q_cold_0=49.734425,
     Q_hot_0=510.45065,
@@ -605,6 +609,7 @@ model MetroscopiaCCGT_direct
     h_0=301935.4)
     annotation (Placement(transformation(extent={{-548,-6},{-536,6}})));
   MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Superheater HPsuperheater2(
+    nominal_DT_default=false,
       QCp_max_side=HPSH_QCp_max_side,
     Q_cold_0=49.734425,
     Q_hot_0=510.45065,

MetroscopeModelingLibrary/Examples/CCGT/MetroscopiaCCGT/MetroscopiaCCGT_reverse.mo

@@ -134,7 +134,7 @@ model MetroscopiaCCGT_reverse
     output Real Q_pumpRec_out; // Observable: controlled by the economizer input temperature
     output Real turbine_compression_rate; // Observable of interest
 
-  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Economiser economiser(
+  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Economiser economiser(nominal_DT_default=false,
       QCp_max_side=Eco_QCp_max_side)
     annotation (Placement(transformation(extent={{74,-56},{132,3}})));
   MetroscopeModelingLibrary.FlueGases.BoundaryConditions.Sink flue_gas_sink
@@ -152,11 +152,11 @@ model MetroscopiaCCGT_reverse
         extent={{-6,6},{6,-6}},
         rotation=180,
         origin={56,8})));
-  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Evaporator evaporator
+  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Evaporator evaporator(faulty=false)
     annotation (Placement(transformation(extent={{-46,-56},{12,4.5}})));
   MetroscopeModelingLibrary.Sensors.WaterSteam.PressureSensor P_w_evap_out_sensor(sensor_function="Calibration", causality="SH1_Kfr")
     annotation (Placement(transformation(extent={{-34,2},{-46,14}})));
-  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Superheater HPsuperheater1(
+  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Superheater HPsuperheater1(nominal_DT_default=false,
       QCp_max_side=HPSH_QCp_max_side)
     annotation (Placement(transformation(extent={{-186,-56},{-126,4}})));
   MetroscopeModelingLibrary.Sensors.WaterSteam.TemperatureSensor T_w_HPSH1_out_sensor(sensor_function="Calibration", causality="SH1_Kth")
@@ -245,7 +245,7 @@ model MetroscopiaCCGT_reverse
     annotation (Placement(transformation(extent={{-346,28},{-334,40}})));
   MetroscopeModelingLibrary.Sensors.FlueGases.TemperatureSensor turbine_T_out_sensor(sensor_function="BC")
     annotation (Placement(transformation(extent={{-370,-32},{-358,-20}})));
-  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Superheater Reheater(
+  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Superheater Reheater(nominal_DT_default=false,
       QCp_max_side=ReH_QCp_max_side)
     annotation (Placement(transformation(extent={{-102,-56},{-42,4}})));
   MetroscopeModelingLibrary.WaterSteam.Machines.SteamTurbine LPsteamTurbine annotation (Placement(transformation(extent={{-14,198},{20,230}})));
@@ -347,7 +347,7 @@ model MetroscopiaCCGT_reverse
   MetroscopeModelingLibrary.Sensors.FlueGases.PressureSensor P_filter_out_sensor(
     display_unit="mbar",                                                         sensor_function="Calibration", causality="filter_Kfr")
     annotation (Placement(transformation(extent={{-548,-32},{-536,-20}})));
-  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Superheater HPsuperheater2(
+  MetroscopeModelingLibrary.MultiFluid.HeatExchangers.Superheater HPsuperheater2(nominal_DT_default=false,
       QCp_max_side=HPSH_QCp_max_side)
     annotation (Placement(transformation(extent={{-302,-56},{-242,4}})));
   MetroscopeModelingLibrary.Sensors.WaterSteam.TemperatureSensor T_w_HPSH2_out_sensor(sensor_function="BC", display_unit="degC")

MetroscopeModelingLibrary/MultiFluid/HeatExchangers/FuelHeater.mo

@@ -9,8 +9,12 @@ model FuelHeater
   // Pressure Losses
   Inputs.InputFrictionCoefficient Kfr_cold;
   Inputs.InputFrictionCoefficient Kfr_hot;
-  Inputs.InputTemperature nominal_cold_side_temperature_rise; // water reference temperature rise based on H&MB diagramm values
-  Inputs.InputTemperature nominal_hot_side_temperature_drop; // flue gases reference temperature rise based on H&MB diagramm values
+
+  // Cp estimation temperatures: estimated temperature differences for both the hot and cold fluids
+  parameter Boolean nominal_DT_default = true;
+  Units.Temperature maximum_achiveable_temperature_difference;
+  Units.Temperature nominal_cold_side_temperature_rise;
+  Units.Temperature nominal_hot_side_temperature_drop;
 
   // Heating
   parameter String QCp_max_side = "undefined";// On fuel heater, QCp_hot may be close to QCp_cold
@@ -126,6 +130,15 @@ equation
   assert(pinch > 0, "A negative pinch is reached", AssertionLevel.warning); // Ensure a positive pinch
   assert(pinch > 1 or pinch < 0,  "A very low pinch (<1) is reached", AssertionLevel.warning); // Ensure a sufficient pinch
 
+  // Nominal temperature differences
+  // The default temperature rise and drop are equal to the maximum achievable temperature difference
+  // Maximum achievable temperature difference for both the hot and cold sides = hot_side.T_in - cold_side.T_in
+  maximum_achiveable_temperature_difference = hot_side.T_in - cold_side.T_in;
+  if nominal_DT_default then
+    nominal_cold_side_temperature_rise = maximum_achiveable_temperature_difference;
+    nominal_hot_side_temperature_drop = maximum_achiveable_temperature_difference;
+  end if;
+
   Cp_cold_min = FuelMedium.specificHeatCapacityCp(cold_side.state_in); // fuel steam inlet Cp
   state_cold_out = FuelMedium.setState_pTX(cold_side.P_in, cold_side.T_in + nominal_cold_side_temperature_rise,cold_side.Xi);
   Cp_cold_max= FuelMedium.specificHeatCapacityCp(state_cold_out); // fuel steam outlet Cp

MetroscopeModelingLibrary/Partial/HeatExchangers/WaterFlueGasesMonophasicHX.mo

@@ -8,8 +8,12 @@ partial model WaterFlueGasesMonophasicHX
   Inputs.InputHeatExchangeCoefficient Kth;
   Inputs.InputFrictionCoefficient Kfr_cold;
   Inputs.InputFrictionCoefficient Kfr_hot;
-  Inputs.InputTemperature nominal_cold_side_temperature_rise; // water reference temperature rise based on H&MB diagramm values
-  Inputs.InputTemperature nominal_hot_side_temperature_drop; // flue gases reference temperature rise based on H&MB diagramm values
+
+  // Cp estimation temperatures: estimated temperature differences for both the hot and cold fluids
+  parameter Boolean nominal_DT_default = true;
+  Units.Temperature maximum_achiveable_temperature_difference;
+  Units.Temperature nominal_cold_side_temperature_rise;
+  Units.Temperature nominal_hot_side_temperature_drop;
 
   parameter String QCp_max_side = "hot";
   // Warning :
@@ -132,8 +136,17 @@ equation
   assert(pinch > 1 or pinch < 0,  "A very low pinch (<1) is reached", AssertionLevel.warning); // Ensure a sufficient pinch
 
   // For each medium, an average Cp is calculated beteween Cp inlet and an estimation of Cp outlet.
-  // The estimation of the Cp outlet is calculated for an outlet temperature based on the nominal temperature rise of the H&MB diagram.
-  // For more details about this hypothesis, please refer the Economiser page of the MML documentation.
+  // The estimation of the Cp outlet is calculated for an outlet temperature based on the nominal temperature rise.
+  // For more details about this hypothesis, please refer the WaterFlueGasesMonophasicHX page of the MML documentation.
+
+  // Nominal temperature differences
+  // The default temperature rise and drop are equal to the maximum achievable temperature difference
+  // Maximum achievable temperature difference for both the hot and cold sides = hot_side.T_in - cold_side.T_in
+  maximum_achiveable_temperature_difference = hot_side.T_in - cold_side.T_in;
+  if nominal_DT_default then
+    nominal_cold_side_temperature_rise = hot_side.T_in - cold_side.T_in;
+    nominal_hot_side_temperature_drop = hot_side.T_in - cold_side.T_in;
+  end if;
 
   Cp_cold_min =MetroscopeModelingLibrary.Utilities.Media.WaterSteamMedium.specificHeatCapacityCp(cold_side.state_in); // water steam inlet Cp
   state_cold_out =MetroscopeModelingLibrary.Utilities.Media.WaterSteamMedium.setState_pTX(

MetroscopeModelingLibrary/Tests/Multifluid/HeatExchangers/Economiser_direct.mo

@@ -14,12 +14,10 @@ model Economiser_direct
   // Parameters
   parameter String QCp_max_side = "hot";
   parameter Utilities.Units.Area S = 10000;
-  parameter Utilities.Units.HeatExchangeCoefficient Kth = 44.5;
-  parameter Utilities.Units.FrictionCoefficient Kfr_hot = 0.0078;
+  parameter Utilities.Units.HeatExchangeCoefficient Kth = 43.2;
+  parameter Utilities.Units.FrictionCoefficient Kfr_hot = 0.0079;
   parameter Utilities.Units.FrictionCoefficient Kfr_cold = 5840;
 
-  parameter Utilities.Units.Temperature nominal_cold_side_temperature_rise = 43;
-  parameter Utilities.Units.Temperature nominal_hot_side_temperature_drop = 27;
 
   .MetroscopeModelingLibrary.WaterSteam.BoundaryConditions.Source cold_source annotation (Placement(transformation(
         extent = {{10,-10},{-10,10}},
@@ -31,7 +29,8 @@ model Economiser_direct
         origin={-66,40})));
   MetroscopeModelingLibrary.FlueGases.BoundaryConditions.Source hot_source annotation (Placement(transformation(extent={{-76,-10},{-56,10}})));
   MetroscopeModelingLibrary.FlueGases.BoundaryConditions.Sink hot_sink annotation (Placement(transformation(extent={{36,-10},{56,10}})));
-  MultiFluid.HeatExchangers.Economiser economiser annotation (Placement(transformation(extent={{-20,-10},{0,10}})));
+  MultiFluid.HeatExchangers.Economiser economiser(nominal_DT_default=true)
+                                                  annotation (Placement(transformation(extent={{-20,-10},{0,10}})));
 equation
 
   // Boundary Conditions
@@ -50,8 +49,7 @@ equation
   economiser.Kth = Kth;
   economiser.Kfr_hot = Kfr_hot;
   economiser.Kfr_cold = Kfr_cold;
-  economiser.nominal_cold_side_temperature_rise = nominal_cold_side_temperature_rise;
-  economiser.nominal_hot_side_temperature_drop = nominal_hot_side_temperature_drop;
+
 
   connect(economiser.C_hot_out, hot_sink.C_in) annotation (Line(
       points={{0,0},{41,0}},

MetroscopeModelingLibrary/Tests/Multifluid/HeatExchangers/Economiser_reverse.mo

@@ -14,8 +14,6 @@ model Economiser_reverse
   // Parameters
   parameter String QCp_max_side = "hot";
   parameter Utilities.Units.Area S = 10000;
-  parameter Utilities.Units.Temperature nominal_cold_side_temperature_rise = 43;
-  parameter Utilities.Units.Temperature nominal_hot_side_temperature_drop = 27;
 
   // Calibrated parameters
   output Utilities.Units.HeatExchangeCoefficient Kth;
@@ -54,8 +52,6 @@ equation
 
   // Parameters
   economiser.S = S;
-  economiser.nominal_cold_side_temperature_rise = nominal_cold_side_temperature_rise;
-  economiser.nominal_hot_side_temperature_drop = nominal_hot_side_temperature_drop;
 
   // Inputs for calibration
   T_cold_out_sensor.T_degC = T_cold_out;
@@ -122,5 +118,6 @@ equation
           pattern = LinePattern.None,
           fillPattern = FillPattern.Solid,
           points = {{-58,-14},{-2,-40},{-58,-74},{-58,-14}})}), Diagram(
-        coordinateSystem(preserveAspectRatio = false, extent={{-100,-100},{100,100}})));
+        coordinateSystem(preserveAspectRatio = false, extent={{-100,-100},{100,100}})),
+    experiment(Interval=0.1, __Dymola_Algorithm="Dassl"));
 end Economiser_reverse;

MetroscopeModelingLibrary/Tests/Multifluid/HeatExchangers/FuelHeater_direct.mo

@@ -15,12 +15,10 @@ model FuelHeater_direct
   // Parameters
   parameter String QCp_max_side = "undefined"; // On fuel heater, QCp_hot may be close to QCp_cold
   parameter Units.Area S = 10;
-  parameter Units.Temperature nominal_cold_side_temperature_rise = 20;
-  parameter Units.Temperature nominal_hot_side_temperature_drop = 10;
 
-  parameter Units.HeatExchangeCoefficient Kth = 8740;
+  parameter Units.HeatExchangeCoefficient Kth = 1357;
   parameter Units.FrictionCoefficient Kfr_hot = 0;
-  parameter Units.FrictionCoefficient Kfr_cold = 1;
+  parameter Units.FrictionCoefficient Kfr_cold = 0;
 
   MetroscopeModelingLibrary.Fuel.BoundaryConditions.Source cold_source annotation (Placement(transformation(extent={{-74,-10},{-54,10}})));
   MetroscopeModelingLibrary.Fuel.BoundaryConditions.Sink cold_sink annotation (Placement(transformation(extent={{54,-10},{74,10}})));
@@ -45,8 +43,6 @@ equation
   cold_source.Xi_out = {0.92,0.048,0.005,0.002,0.015,0.01};
 
   fuelHeater.S = S;
-  fuelHeater.nominal_cold_side_temperature_rise = nominal_cold_side_temperature_rise;
-  fuelHeater.nominal_hot_side_temperature_drop = nominal_hot_side_temperature_drop;
 
   fuelHeater.Kth = Kth;
   fuelHeater.Kfr_hot = Kfr_hot;

MetroscopeModelingLibrary/Tests/Multifluid/HeatExchangers/FuelHeater_reverse.mo

@@ -13,8 +13,6 @@ model FuelHeater_reverse
   // Parameters
   parameter String QCp_max_side = "undefined"; // On fuel heater, QCp_hot may be close to QCp_cold
   parameter Utilities.Units.Area S=100;
-  parameter Utilities.Units.Temperature nominal_cold_side_temperature_rise=20;
-  parameter Utilities.Units.Temperature nominal_hot_side_temperature_drop=10;
 
   // Calibrated parameters
   output Utilities.Units.HeatExchangeCoefficient Kth;
@@ -61,10 +59,8 @@ equation
 
   // Parameters
   fuelHeater.S = S;
-  fuelHeater.nominal_cold_side_temperature_rise = nominal_cold_side_temperature_rise;
-  fuelHeater.nominal_hot_side_temperature_drop = nominal_hot_side_temperature_drop;
 
-    // Inputs for calibration
+  // Inputs for calibration
   T_hot_out_sensor.T_degC = T_hot_out;
   //cold_sink.T_in = T_cold_out +273.15;
   P_cold_out_sensor.P_barA = P_cold_out;

MetroscopeModelingLibrary/Tests/Multifluid/HeatExchangers/Superheater_direct.mo

@@ -15,12 +15,10 @@ model Superheater_direct
   parameter String QCp_max_side = "hot";
   parameter Utilities.Units.Area S = 10000;
   parameter Utilities.Units.FrictionCoefficient Kfr_hot = 0;
-  parameter Utilities.Units.Temperature nominal_cold_side_temperature_rise = 105;
-  parameter Utilities.Units.Temperature nominal_hot_side_temperature_drop = 35;
 
   // Calibrated parameters
-  parameter Utilities.Units.HeatExchangeCoefficient Kth = 22.659254;
-  parameter Utilities.Units.FrictionCoefficient Kfr_cold = 351.14395;
+  parameter Utilities.Units.HeatExchangeCoefficient Kth = 23.04;
+  parameter Utilities.Units.FrictionCoefficient Kfr_cold = 351.82;
 
   .MetroscopeModelingLibrary.WaterSteam.BoundaryConditions.Source cold_source annotation (Placement(transformation(
         extent = {{10,-10},{-10,10}},
@@ -47,8 +45,6 @@ equation
   superheater.Kth = Kth;
   superheater.Kfr_hot = Kfr_hot;
   superheater.Kfr_cold = Kfr_cold;
-  superheater.nominal_cold_side_temperature_rise = nominal_cold_side_temperature_rise;
-  superheater.nominal_hot_side_temperature_drop = nominal_hot_side_temperature_drop;
 
   connect(superheater.C_hot_in, hot_source.C_out) annotation (Line(
       points={{-10,0},{-61,0}},