Modelica.Fluid.Valves.BaseClasses.ValveCharacteristics

Information

Package Content

Name	Description
baseFun	Base class for valve characteristics
linear	Linear characteristic
one	Constant characteristic
quadratic	Quadratic characteristic
equalPercentage	Equal percentage characteristic

Modelica.Fluid.Valves.BaseClasses.ValveCharacteristics.baseFun

Information

This is a partial function that defines the interface of valve characteristics. The function returns "rc = valveCharacteristic" as function of the opening "pos" (in the range 0..1):

    dp = (zeta_TOT/2) * rho * velocity^2
m_flow =    sqrt(2/zeta_TOT) * Av * sqrt(rho * dp)
m_flow = valveCharacteristic * Av * sqrt(rho * dp)
m_flow =                  rc * Av * sqrt(rho * dp)

Extends from Modelica.Icons.Function (Icon for functions).

Inputs

Type	Name	Default	Description
Real	pos		Opening position (0: closed, 1: fully open)

Outputs

Type	Name	Description
Real	rc	Relative flow coefficient (per unit)

Modelica definition

partial function baseFun "Base class for valve characteristics"
  extends Modelica.Icons.Function;
  input Real pos(min=0, max=1) "Opening position (0: closed, 1: fully open)";
  output Real rc "Relative flow coefficient (per unit)";
end baseFun;

Modelica.Fluid.Valves.BaseClasses.ValveCharacteristics.linear

Information

Inputs

Type	Name	Default	Description
Real	pos		Opening position (0: closed, 1: fully open)

Outputs

Type	Name	Description
Real	rc	Relative flow coefficient (per unit)

Modelica definition

function linear "Linear characteristic"
  extends baseFun;
algorithm 
  rc := pos;
end linear;

Modelica.Fluid.Valves.BaseClasses.ValveCharacteristics.one

Information

Inputs

Type	Name	Default	Description
Real	pos		Opening position (0: closed, 1: fully open)

Outputs

Type	Name	Description
Real	rc	Relative flow coefficient (per unit)

Modelica definition

function one "Constant characteristic"
  extends baseFun;
algorithm 
  rc := 1;
end one;

Modelica.Fluid.Valves.BaseClasses.ValveCharacteristics.quadratic

Information

Inputs

Type	Name	Default	Description
Real	pos		Opening position (0: closed, 1: fully open)

Outputs

Type	Name	Description
Real	rc	Relative flow coefficient (per unit)

Modelica definition

function quadratic "Quadratic characteristic"
  extends baseFun;
algorithm 
  rc := pos*pos;
end quadratic;

Modelica.Fluid.Valves.BaseClasses.ValveCharacteristics.equalPercentage

Information

d(rc)/d(pos) = k d(pos).

The constant k is expressed in terms of the rangeability, i.e., the ratio between the maximum and the minimum useful flow coefficient:

rangeability = exp(k) = rc(1.0)/rc(0.0).

The theoretical characteristic has a non-zero opening when pos = 0; the implemented characteristic is modified so that the valve closes linearly when pos < delta.

Extends from baseFun (Base class for valve characteristics).

Inputs

Type	Name	Default	Description
Real	pos		Opening position (0: closed, 1: fully open)
Real	rangeability	20	Rangeability
Real	delta	0.01

Outputs

Type	Name	Description
Real	rc	Relative flow coefficient (per unit)

Modelica definition

function equalPercentage "Equal percentage characteristic"
  extends baseFun;
  input Real rangeability = 20 "Rangeability";
  input Real delta = 0.01;
algorithm 
  rc := if pos > delta then rangeability^(pos-1) else 
          pos/delta*rangeability^(delta-1);
end equalPercentage;