Package Modelica.​Fluid.​Valves.​BaseClasses
Base classes used in the Valves package (only of interest to build new component models)

Information

This icon shall be used for a package/library that contains base models and classes, respectively.

Extends from Modelica.​Icons.​BasesPackage (Icon for packages containing base classes).

Package Contents

NameDescription
PartialValveBase model for valves
ValveCharacteristicsFunctions for valve characteristics

Partial Model Modelica.​Fluid.​Valves.​BaseClasses.​PartialValve
Base model for valves

Information

This is the base model for the ValveIncompressible, ValveVaporizing, and ValveCompressible valve models. The model is based on the IEC 534 / ISA S.75 standards for valve sizing.

The model optionally supports reverse flow conditions (assuming symmetrical behaviour) or check valve operation, and has been suitably regularized, compared to the equations in the standard, in order to avoid numerical singularities around zero pressure drop operating conditions.

The model assumes adiabatic operation (no heat losses to the ambient); changes in kinetic energy from inlet to outlet are neglected in the energy balance.

Modelling options

The following options are available to specify the valve flow coefficient in fully open conditions:

The nominal pressure drop dp_nominal must always be specified; to avoid numerical singularities, the flow characteristic is modified for pressure drops less than b*dp_nominal (the default value is 1% of the nominal pressure drop). Increase this parameter if numerical problems occur in valves with very low pressure drops.

If checkValve is true, then the flow is stopped when the outlet pressure is higher than the inlet pressure; otherwise, reverse flow takes place. Use this option only when needed, as it increases the numerical complexity of the problem.

The valve opening characteristic valveCharacteristic, linear by default, can be replaced by any user-defined function. Quadratic and equal percentage with customizable rangeability are already provided by the library. The characteristics for constant port_a.p and port_b.p pressures with continuously changing opening are shown in the next two figures:

ValveCharacteristics1a.png
Components/ValveCharacteristics1b.png

The treatment of parameters Kv and Cv is explained in detail in the User's Guide.

With the optional parameter "filteredOpening", the opening can be filtered with a second order, criticalDamping filter so that the opening demand is delayed by parameter "riseTime". The filtered opening is then available via the output signal "opening_filtered" and is used to control the valve equations. This approach approximates the driving device of a valve. The "riseTime" parameter is used to compute the cut-off frequency of the filter by the equation: f_cut = 5/(2*pi*riseTime). It defines the time that is needed until opening_filtered reaches 99.6 % of a step input of opening. The icon of a valve changes in the following way (left image: filteredOpening=false, right image: filteredOpening=true):

FilteredValveIcon.png

If "filteredOpening = true", the input signal "opening" is limited by parameter leakageOpening, i.e., if "opening" becomes smaller as "leakageOpening", then "leakageOpening" is used instead of "opening" as input for the filter. The reason is that "opening=0" might structurally change the equations of the fluid network leading to a singularity. If a small leakage flow is introduced (which is often anyway present in reality), the singularity might be avoided.

In the next figure, "opening" and "filtered_opening" are shown in the case that filteredOpening = true, riseTime = 1 s, and leakageOpening = 0.02.

ValveFilteredOpening.png

Extends from Modelica.​Fluid.​Interfaces.​PartialTwoPortTransport (Partial element transporting fluid between two ports without storage of mass or energy).

Parameters

TypeNameDefaultDescription
BooleanallowFlowReversalsystem.​allowFlowReversal= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
AbsolutePressuredp_startdp_nominalGuess value of dp = port_a.p - port_b.p
MassFlowRatem_flow_startm_flow_nominalGuess value of m_flow = port_a.m_flow
MassFlowRatem_flow_smallif system.use_eps_Re then system.eps_m_flow * m_flow_nominal else system.m_flow_smallSmall mass flow rate for regularization of zero flow
Booleanshow_Ttrue= true, if temperatures at port_a and port_b are computed
Booleanshow_V_flowtrue= true, if volume flow rate at inflowing port is computed
CvTypesCvDataModelica.​Fluid.​Types.​CvTypes.​OpPointSelection of flow coefficient
AreaAv Av (metric) flow coefficient
RealKv0Kv (metric) flow coefficient [m3/h]
RealCv0Cv (US) flow coefficient [USG/min]
Pressuredp_nominal Nominal pressure drop
MassFlowRatem_flow_nominal Nominal mass flowrate
Densityrho_nominalMedium.density_pTX(Medium.p_default, Medium.T_default, Medium.X_default)Nominal inlet density
Realopening_nominal1Nominal opening
BooleanfilteredOpeningfalse= true, if opening is filtered with a 2nd order CriticalDamping filter
TimeriseTime1Rise time of the filter (time to reach 99.6 % of an opening step)
RealleakageOpening0.001The opening signal is limited by leakageOpening (to improve the numerics)
BooleancheckValvefalseReverse flow stopped

Connectors

TypeNameDescription
FluidPort_aport_aFluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_bport_bFluid connector b (positive design flow direction is from port_a to port_b)
input RealInputopeningValve position in the range 0..1
output RealOutputopening_filteredFiltered valve position in the range 0..1

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