Buildings.Fluids.BaseClasses

Information

Extends from Modelica_Fluid.Icons.BaseClassLibrary (Icon for library).

Package Content

Name	Description
FlowModels	Flow models for pressure drop calculations
PartialResistance	Partial model for a hydraulic resistance
PartialThreeWayResistance	Flow splitter with partial resistance model at each port

Buildings.Fluids.BaseClasses.PartialResistance

Information

Partial model for a flow resistance, possible with variable flow coefficient. The pressure drop is computed by an instance of Buildings.Fluids.BaseClasses.FlowModels.BasicFlowModel, i.e., using a regularized implementation of the equation

  m_flow = sign(dp) * k * sqrt(|dp|).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
Pressure	dp_nominal		Pressure [Pa]
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
AbsolutePressure	dp_start	0.01*system.p_start	Guess value of dp = port_a.p - port_b.p [Pa]
MassFlowRate	m_flow_start	system.m_flow_start	Guess value of m_flow = port_a.m_flow [kg/s]
MassFlowRate	m_flow_small	1E-4*m_flow_nominal	Small mass flow rate for regularization of zero flow [kg/s]
Boolean	from_dp	true	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearized	false	= true, use linear relation between m_flow and dp for any flow rate
Diagnostics
Boolean	show_T	true	= true, if temperatures at port_a and port_b are computed
Boolean	show_V_flow	true	= true, if volume flow rate at inflowing port is computed

Connectors

Type	Name	Description
FluidPort_a	port_a	Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b	port_b	Fluid connector b (positive design flow direction is from port_a to port_b)

Modelica definition

partial model PartialResistance 
  "Partial model for a hydraulic resistance"
    extends Modelica_Fluid.Interfaces.PartialTwoPortTransport(m_flow_small = 1E-4*m_flow_nominal,
     m_flow(nominal=m_flow_nominal), dp(nominal=dp_nominal, displayUnit="Pa"));


  parameter Boolean from_dp = true 
    "= true, use m_flow = f(dp) else dp = f(m_flow)";
  parameter Medium.MassFlowRate m_flow_nominal(min=0) "Nominal mass flow rate";
  parameter Modelica.SIunits.Pressure dp_nominal(min=0, displayUnit="Pa") 
    "Pressure";
  parameter Boolean linearized = false 
    "= true, use linear relation between m_flow and dp for any flow rate";

  Real k(unit="") "Flow coefficient, k=m_flow/sqrt(dp), with unit=(kg.m)^(1/2)";
  Medium.MassFlowRate m_flow_turbulent 
    "Turbulent flow if |m_flow| >= m_flow_turbulent, not a parameter because k can be a function of time";

//  Modelica.SIunits.Pressure dp_turbulent
//    "Turbulent flow if |dp| >= dp_small, not a parameter because k can be a function of time";

protected 
  parameter Medium.ThermodynamicState sta0=
     Medium.setState_pTX(T=Medium.T_default, p=Medium.p_default, X=Medium.X_default);
  parameter Modelica.SIunits.DynamicViscosity eta_nominal=Medium.dynamicViscosity(sta0) 
    "Dynamic viscosity, used to compute transition to turbulent flow regime";
  parameter Modelica.SIunits.SpecificEnthalpy h0=Medium.h_default 
    "Initial value for solver for specific enthalpy";           //specificEnthalpy(sta0)
 constant Real conv(unit="m.s2/kg") = 1 "Factor, needed to satisfy unit check";
 constant Real conv2 = sqrt(conv) "Factor, needed to satisfy unit check";
equation 
  // Pressure drop calculation
  if from_dp then
    m_flow=FlowModels.basicFlowFunction_dp(dp=dp, k=k, m_flow_turbulent=m_flow_turbulent, linearized=linearized);
  else
    dp=FlowModels.basicFlowFunction_m_flow(m_flow=m_flow, k=k, m_flow_turbulent=m_flow_turbulent, linearized=linearized);
  end if;

  // Isenthalpic state transformation (no storage and no loss of energy)
  port_a.h_outflow = inStream(port_b.h_outflow);
  port_b.h_outflow = inStream(port_a.h_outflow);

end PartialResistance;

Buildings.Fluids.BaseClasses.PartialThreeWayResistance

Information

Partial model for flow resistances with three ports such as a flow mixer/splitter or a three way valve.

Parameters

Type	Name	Default	Description
PartialTwoPortTransport	res1	redeclare Modelica_Fluid.Int...	Partial model, to be replaced with a fluid component
PartialTwoPortTransport	res2	redeclare Modelica_Fluid.Int...	Partial model, to be replaced with a fluid component
PartialTwoPortTransport	res3	redeclare Modelica_Fluid.Int...	Partial model, to be replaced with a fluid component
Advanced
Boolean	from_dp	true	= true, use m_flow = f(dp) else dp = f(m_flow)

Connectors

Type	Name	Description
FluidPort_a	port_1
FluidPort_b	port_2
FluidPort_a	port_3

Modelica definition

partial model PartialThreeWayResistance 
  "Flow splitter with partial resistance model at each port"
  replaceable package Medium = Modelica.Media.Interfaces.PartialMedium 
    "Fluid medium model";

  Modelica_Fluid.Interfaces.FluidPort_a port_1(redeclare package Medium = 
        Medium, m_flow(min=if (portFlowDirection_1 == Modelica_Fluid.Types.PortFlowDirection.Entering) then 
                0.0 else -Modelica.Constants.inf, max=if (portFlowDirection_1
           == Modelica_Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf));
  Modelica_Fluid.Interfaces.FluidPort_b port_2(redeclare package Medium = 
        Medium, m_flow(min=if (portFlowDirection_2 == Modelica_Fluid.Types.PortFlowDirection.Entering) then 
                0.0 else -Modelica.Constants.inf, max=if (portFlowDirection_2
           == Modelica_Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf));
  Modelica_Fluid.Interfaces.FluidPort_a port_3(
    redeclare package Medium=Medium,
    m_flow(min=if (portFlowDirection_3==Modelica_Fluid.Types.PortFlowDirection.Entering) then 0.0 else -Modelica.Constants.inf,
    max=if (portFlowDirection_3==Modelica_Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf));

 parameter Boolean from_dp = true 
    "= true, use m_flow = f(dp) else dp = f(m_flow)";
  replaceable Modelica_Fluid.Interfaces.PartialTwoPortTransport res1(redeclare 
      package Medium = Medium) 
    "Partial model, to be replaced with a fluid component";
  replaceable Modelica_Fluid.Interfaces.PartialTwoPortTransport res2(redeclare 
      package Medium = Medium) 
    "Partial model, to be replaced with a fluid component";
  replaceable Modelica_Fluid.Interfaces.PartialTwoPortTransport res3(redeclare 
      package Medium = Medium) 
    "Partial model, to be replaced with a fluid component";

protected 
  parameter Modelica_Fluid.Types.PortFlowDirection portFlowDirection_1=Modelica_Fluid.Types.PortFlowDirection.Bidirectional 
    "Flow direction for port_1";
  parameter Modelica_Fluid.Types.PortFlowDirection portFlowDirection_2=Modelica_Fluid.Types.PortFlowDirection.Bidirectional 
    "Flow direction for port_2";
  parameter Modelica_Fluid.Types.PortFlowDirection portFlowDirection_3=Modelica_Fluid.Types.PortFlowDirection.Bidirectional 
    "Flow direction for port_3";

equation 
  connect(port_1, res1.port_a);
  connect(res2.port_b, port_2);
  connect(res3.port_a, port_3);
  connect(res1.port_b, res2.port_a);
  connect(res1.port_b, res3.port_b);
end PartialThreeWayResistance;