Buildings.Fluids.FixedResistances

Package Content

Name	Description
Examples	Collection of models that illustrate model use and test models
FixedResistanceDpM	Fixed flow resistance with dp and m_flow as parameter
LosslessPipe	Pipe with no flow friction and no heat transfer
SplitterFixedResistanceDpM	Flow splitter with fixed resistance at each port

Buildings.Fluids.FixedResistances.FixedResistanceDpM

Information

This is a model of a resistance with a fixed flow coefficient k = m_flow/sqrt(dP).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Boolean	use_dh	false	Set to true to specify hydraulic diameter
Length	dh	1	Hydraulic diameter [m]
Real	ReC	4000	Reynolds number where transition to turbulent starts
Real	deltaM	0.3	Fraction of nominal mass flow rate where transition to turbulent occurs
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

model FixedResistanceDpM 
  "Fixed flow resistance with dp and m_flow as parameter"
  extends Buildings.Fluids.BaseClasses.PartialResistance;
  parameter Boolean use_dh = false "Set to true to specify hydraulic diameter";
  parameter Modelica.SIunits.Length dh=1 "Hydraulic diameter";
  parameter Real ReC=4000 
    "Reynolds number where transition to turbulent starts";
  parameter Real deltaM(min=0.01) = 0.3 
    "Fraction of nominal mass flow rate where transition to turbulent occurs";
initial equation 
 if ( m_flow_turbulent > m_flow_nominal) then
   Modelica.Utilities.Streams.print("Warning: In FixedResistanceDpM, m_flow_nominal is smaller than m_flow_turbulent."
           + "\n"
           + "  m_flow_nominal = " + realString(m_flow_nominal) + "\n"
           + "  dh      = " + realString(dh) + "\n"
           + "  To fix, set dh < " +
                realString(     4*m_flow_nominal/eta_nominal/Modelica.Constants.pi/ReC) + "\n"
           + "  Suggested value: dh = " +
                realString(1/10*4*m_flow_nominal/eta_nominal/Modelica.Constants.pi/ReC));
 end if;

equation 
 m_flow_turbulent = if use_dh then 
                      eta_nominal*dh/4*Modelica.Constants.pi*ReC else 
                      deltaM * m_flow_nominal;
  if linearized then
   k = m_flow_nominal / dp_nominal / conv2;
  else
   k = m_flow_nominal / sqrt(dp_nominal);
 end if;
end FixedResistanceDpM;

Buildings.Fluids.FixedResistances.LosslessPipe

Information

Model of a pipe with no flow resistance and no heat loss. This model can be used to replace a replaceable pipe model in flow legs in which no friction should be modeled, such as in the outlet port of a three way valve.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
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	system.m_flow_small	Small mass flow rate for regularization of zero flow [kg/s]
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

model LosslessPipe "Pipe with no flow friction and no heat transfer"
  extends Modelica_Fluid.Interfaces.PartialTwoPortTransport;
  extends Buildings.BaseClasses.BaseIcon;
equation 
 dp=0;
  // 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 LosslessPipe;

Buildings.Fluids.FixedResistances.SplitterFixedResistanceDpM

Information

Model of a flow splitter (or mixer) with a fixed resistance in each flow leg.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Fluid medium model
Boolean	use_dh	false	Set to true to specify hydraulic diameter
Real	deltaM	0.3	Fraction of nominal mass flow rate where transition to turbulent occurs
Length	dh[3]	{1,1,1}	Hydraulic diameter [m]
Real	ReC[3]	{4000,4000,4000}	Reynolds number where transition to turbulent starts
Nominal condition
MassFlowRate	m_flow_nominal[3]		Mass flow rate [kg/s]
Pressure	dp_nominal[3]		Pressure [Pa]
Advanced
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

Connectors

Type	Name	Description
FluidPort_a	port_1
FluidPort_b	port_2
FluidPort_a	port_3

Modelica definition

model SplitterFixedResistanceDpM 
  "Flow splitter with fixed resistance at each port"
    extends Buildings.Fluids.BaseClasses.PartialThreeWayResistance(
      redeclare Buildings.Fluids.FixedResistances.FixedResistanceDpM res1(
         redeclare package Medium=Medium,
         from_dp=from_dp, m_flow_nominal=m_flow_nominal[1], dp_nominal=dp_nominal[1],
         ReC=ReC[1], dh=dh[1],
         linearized=linearized, deltaM=deltaM),
      redeclare Buildings.Fluids.FixedResistances.FixedResistanceDpM res2(
         redeclare package Medium=Medium,
         from_dp=from_dp, m_flow_nominal=m_flow_nominal[2], dp_nominal=dp_nominal[2],
         ReC=ReC[2], dh=dh[2],
         linearized=linearized, deltaM=deltaM),
      redeclare Buildings.Fluids.FixedResistances.FixedResistanceDpM res3(
         redeclare package Medium=Medium,
         from_dp=from_dp, m_flow_nominal=m_flow_nominal[3], dp_nominal=dp_nominal[3],
         ReC=ReC[3], dh=dh[3],
         linearized=linearized, deltaM=deltaM));


  parameter Boolean use_dh = false "Set to true to specify hydraulic diameter";
  parameter Modelica.SIunits.MassFlowRate[3] m_flow_nominal(each min=0) 
    "Mass flow rate";
  parameter Modelica.SIunits.Pressure[3] dp_nominal(each min=0) "Pressure";
  parameter Real deltaM(min=0) = 0.3 
    "Fraction of nominal mass flow rate where transition to turbulent occurs";

  parameter Modelica.SIunits.Length[3] dh={1, 1, 1} "Hydraulic diameter";
  parameter Real[3] ReC={4000, 4000, 4000} 
    "Reynolds number where transition to turbulent starts";
  parameter Boolean linearized = false 
    "= true, use linear relation between m_flow and dp for any flow rate";
end SplitterFixedResistanceDpM;