modelValve
Extends from Icons.Gas.Valve.
Information
This model is based on the IEC 534/ISA S.75 standards for valve sizing, compressible fluid.
The model optionally supports reverse flow conditions (assuming symmetrical behaviour) or check valve operation, and has been suitably modified to avoid numerical singularities at zero pressure drop.
The model operating range include choked flow operation, due to sonic conditions in the vena contracta.
The flow characteristic can be customised.
Modelling options
The actual gas used in the component is determined by the replaceable Medium package. In the case of multiple component, variable composition gases, the start composition is given by Xstart,whose default value is Medium.reference_X.
The following options are available to specify the valve flow coefficient in fully open conditions:
- CvData = 0: the flow coefficient is given by the metric Av coefficient Av (m^2).
- CvData = 1: the flow coefficient is given by the metric Kv coefficient Kv (m^3/h).
- CvData = 2: the flow coefficient is given by the US Cv coefficient Cv (USG/min).
- CvData = 3: the flow coefficient must be specified by an additional initial equation (e.g. w=0.5); the start value given by Av is used to initialise the numerical solution of the equation.
The nominal inlet pressure pnom and pressure drop dpnom must always be specified; to avoid numerical singularities, the flow characteristic is modified for pressure drops less than b*dpnom (the default value is 1% of the nominal pressure drop). Increase this parameter if numerical instabilities 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.
The default flow characteristic FlowChar is linear; this can be replaced by any user-defined function (e.g. equal percentage, quick opening, etc.).
The product Fk*xt is given by the parameter Fxtnom, and is assumed constant by default. The relative change of the xt coefficient with the valve opening can be specified by customising the xtfun function.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Boolean | fixedAv | (if CvData == ThermoPower.Choices.Valve.CvTypes.Av then true else false) | |
| Boolean | CheckValve | false | Reverse flow stopped |
| SI.PerUnit | b | 0.01 | Regularisation factor |
| SI.PerUnit | Fxt_full | 0.5 | Fk*xt critical ratio at full opening |
| Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction |
| Flow Coefficient | |||
| ThermoPower.Choices.Valve.CvTypes | CvData | ThermoPower.Choices.Valve.CvTypes.Av | Selection of flow coefficient |
| SI.Area | Av | Av (metric) flow coefficient | |
| Real | Kv | 0 | Kv (metric) flow coefficient |
| Real | Cv | 0 | Cv (US) flow coefficient [USG/min] |
| Valve Opening | |||
| Boolean | useThetaInput | true | Use the input connector for the valve opening |
| SI.PerUnit | theta_fix | 1 | Fixed opening value when the input connector not used |
| Nominal operating point | |||
| Medium.AbsolutePressure | pnom | Nominal inlet pressure | |
| SI.PressureDifference | dpnom | Nominal pressure drop | |
| Medium.MassFlowRate | wnom | Nominal mass flowrate | |
| Medium.Density | rhonom | 1000 | Nominal density |
| SI.PerUnit | thetanom | 1 | Nominal valve opening |
| Initialisation | |||
| Medium.AbsolutePressure | pin_start | pnom | Inlet pressure start value |
| Medium.AbsolutePressure | pout_start | pnom - dpnom | Inlet pressure start value |
| Medium.Temperature | Tstart | 300 | Start temperature |
| Medium.MassFraction[Medium.nX] | Xstart | Medium.reference_X | Start gas composition |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| FlangeA | inlet | ||
| FlangeB | outlet | ||
| Modelica.Blocks.Interfaces.RealInput | theta |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Medium.BaseProperties | gas | ||
| ThermoPower.System | system | System wide properties | |
| Medium.MassFlowRate | w | Mass Flow Rate | |
| SI.PressureDifference | dp | Pressure drop | |
| SI.PerUnit | Fxt | ||
| SI.PerUnit | x | Pressure drop ratio | |
| SI.PerUnit | xs | Saturated pressure drop ratio | |
| SI.PerUnit | Y | Compressibility factor | |
| SI.PerUnit | theta_act | Actual valve opening | |
| Medium.AbsolutePressure | p | Inlet pressure |
Contents
| Name | Description |
|---|---|
 Medium | |
 FlowChar | |
 xtfun | |
 sqrtRprotected |
Revisions
- 15 Mar 2005
by Francesco Casella:
Rewritten with sqrtReg. - 19 Nov 2004
by Francesco Casella:
Adapted to Modelica.Media. - 5 Mar 2004
by Francesco Casella:
First release.
Avnom removed, Av can now be set directly. Kvnom and Cvnom renamed to Kv and Cv.
CvData=3 no longer uses dpnom,wnom and rhonom, and requires an additional initial equation to set the flow coefficient based on the initial working conditions.