# Orifice (2P)

Constant- or variable-area orifice in a two-phase fluid network

Since R2021a

Libraries:
Simscape / Fluids / Two-Phase Fluid / Valves & Orifices

## Description

The Orifice (2P) block models pressure loss due to a constant or variable area orifice in a two-phase fluid network. The Modeling option parameter controls the parameterization options for a valve designed for modeling either vapor or liquid, but does not impact the fluid properties. The block calculates fluid properties inside the valve from inlet conditions. There is no heat exchange between the fluid and the environment, and therefore phase change inside the orifice only occurs due to a pressure drop or a propagated phase change from another part of the model.

The orifice can be constant or variable. When Orifice type is `Variable`, the physical signal at port S sets the position of the control member, which opens and closes the orifice.

### Liquid Orifice

When Modeling option is ```Liquid operating condition```, the block parameterizations depend on the value of the Orifice type parameter. The block calculates the pressure loss and pressure recovery in the same way for all liquid parameterization options.

The block accounts for pressure loss by using the ratio of the pressure loss across the whole orifice to the pressure drop immediately across the orifice plate. This ratio, PRloss, is

`$P{R}_{loss}=\frac{\sqrt{1-{\left(\frac{{A}_{orifice}}{{A}_{port}}\right)}^{2}\left(1-{C}_{d}^{2}\right)}-{C}_{d}\frac{{A}_{orifice}}{{A}_{port}}}{\sqrt{1-{\left(\frac{{A}_{orifice}}{{A}_{port}}\right)}^{2}\left(1-{C}_{d}^{2}\right)}+{C}_{d}\frac{{A}_{orifice}}{{A}_{port}}},$`

where:

• Cd is the value of the Discharge coefficient parameter.

• Aorifice is the instantaneous orifice open area.

• Aport is the value of the Cross-sectional area at ports A and B parameter.

The pressure recovery is the positive pressure change in the valve due to an increase in area after the orifice hole. If you do not want to capture this increase in pressure, clear the Pressure recovery check box. In this case, PRloss is 1, which reduces the model complexity. Clear this setting if the orifice hole is quite small relative to the port area or if the next downstream component is close to the block and any jet does not have room to dissipate.

The critical pressure difference, Δpcrit, is the pressure differential where the flow transitions between laminar and turbulent flow,

`$\Delta {p}_{crit}=\frac{\left({p}_{A}+{p}_{B}\right)}{2}\left(1-{B}_{lam}\right),$`

where:

• pA and pB are the pressure at port A and B, respectively.

• Blam is the value of the Laminar flow pressure ratio parameter.

Nominal Mass Flow Rate Parameterization

When you set Orifice type to `Constant` and Orifice Parameterization to ```Nominal mass flow rate```, the mass flow rate through the orifice is

`$\stackrel{˙}{m}={\stackrel{˙}{m}}_{nom}\left[\sqrt{\frac{{v}_{nom}}{2\Delta {p}_{nom}}}\right]\sqrt{\frac{2}{{v}_{in}}}\frac{\Delta p}{{\left(\Delta {p}^{2}+\Delta {p}_{crit}^{2}\right)}^{0.25}},$`

where:

• ${\stackrel{˙}{m}}_{nom}$ is the value of the Nominal mass flow rate parameter.

• Δpnom is the value of the Nominal pressure drop rate parameter.

• vnom is the nominal inlet specific volume. The block determines this value from the tabulated fluid properties data based on the value of the Nominal inlet condition specification parameter.

• vin is the inlet specific volume.

Liquid Orifice Area Parameterization

When you set Orifice type to `Constant` and Orifice Parameterization to ```Orifice area```, the block calculates the mass flow rate as

`$\stackrel{˙}{m}=\frac{{C}_{d}{A}_{orifice}\sqrt{\frac{2}{{v}_{in}}}}{\sqrt{P{R}_{loss}\left(1-{\left(\frac{{A}_{orifice}}{{A}_{port}}\right)}^{2}\right)}}\sqrt{\Delta p}\approx \frac{{C}_{d}{A}_{orifice}\sqrt{2\frac{2}{{v}_{in}}}}{\sqrt{P{R}_{loss}\left(1-{\left(\frac{{A}_{orifice}}{{A}_{port}}\right)}^{2}\right)}}\frac{\Delta p}{{\left[\Delta {p}^{2}+\Delta {p}_{crit}\right]}^{1/4}},$`

where Δp is the pressure drop over the orifice, pA ̶ pB.

Linear - Nominal Mass Flow Rate vs. Control Member Position Parameterization

When you set Orifice type to `Variable` and Orifice Parameterization to ```Nominal mass flow rate vs. control member position```, the mass flow rate through the variable-area orifice is

`$\stackrel{˙}{m}=\lambda {\stackrel{˙}{m}}_{nom}\left[\sqrt{\frac{{v}_{nom}}{2\Delta {p}_{nom}}}\right]\sqrt{\frac{2}{{v}_{in}}}\frac{\Delta p}{{\left(\Delta {p}^{2}+\Delta {p}_{crit}^{2}\right)}^{0.25}},$`

where λ is the orifice opening fraction, which is a fraction of the total orifice open area.

The block determines the orifice opening for all variable orifice parameterizations as

`$\lambda =\epsilon \left(1-{f}_{leak}\right)\frac{\left(S-{S}_{\mathrm{min}}\right)}{\Delta S}+{f}_{leak},$`

where:

• ε is `1` when Opening orientation is ```Positive control member displacement opens orifice``` and `-1` when Opening orientation is ```Negative control member displacement opens orifice```.

• fleak is the value of the Leakage flow fraction parameter.

• S is th value of the signal at port S.

• Smin is the value of the Control member position at closed orifice parameter.

• ΔS is the value of the Control member travel between closed and open orifice parameter.

Linear - Area vs. Control Member Position Parameterization

When you set Orifice type to `Variable` and Orifice Parameterization to ```Linear - Area vs. control member position```, the orifice area is

`${A}_{orifice}=\lambda {A}_{\mathrm{max}},$`

where Amax is the value of the Maximum orifice area parameter.

The mass flow rate is

`$\stackrel{˙}{m}=\frac{{C}_{d}{A}_{orifice}\sqrt{\frac{2}{{v}_{in}}}}{\sqrt{P{R}_{loss}\left(1-{\left(\frac{{A}_{orifice}}{{A}_{port}}\right)}^{2}\right)}}\frac{\Delta p}{{\left[\Delta {p}^{2}+\Delta {p}_{crit}^{2}\right]}^{1/4}}.$`

When the orifice is in a near-open or near-closed position, you can maintain numerical robustness in your simulation by adjusting the parameter. If the parameter is nonzero, the block smoothly saturates the opening area between Aleak and Amax, where Aleak = fleakAmax. For more information, see Numerical Smoothing.

Tabulated Data - Area vs. Control Member Position Parameterization

When you set Orifice type to `Variable` and Orifice Parameterization to ```Tabulated data - Area vs. control member position```, the block interpolates the orifice area, Aorifice, from the Orifice area vector and Control member position vector parameters. The signal at port S specifies the control member position. The block uses linear interpolation to query between the data points and nearest extrapolation for points beyond the table boundaries.

The block uses the same equation as the ```Linear - Area vs. control member position``` setting to calculate the volumetric flow rate.

Fluid Specific Volume Dynamics

For all parameterizations, the block calculates the fluid specific volume during simulation based on the liquid state.

If the fluid at the orifice inlet is a liquid-vapor mixture, the block calculates the specific volume as

`${v}_{in}=\left(1-{x}_{dyn}\right){v}_{liq}+{x}_{dyn}{v}_{vap},$`

where:

• xdyn is the inlet vapor quality. The block applies a first-order lag to the inlet vapor quality of the mixture.

• vliq is the liquid specific volume of the fluid.

• vvap is the vapor specific volume of the fluid.

If the inlet fluid is liquid or vapor, vin is the respective liquid or vapor specific volume.

If the inlet vapor quality is a liquid-vapor mixture, the block applies a first-order time lag,

`$\frac{d{x}_{dyn}}{dt}=\frac{{x}_{in}-{x}_{dyn}}{\tau },$`

where:

• xdyn is the dynamic vapor quality.

• xin is the current inlet vapor quality.

• τ is the value of the Inlet phase change time constant parameter.

If the inlet fluid is a subcooled liquid, xin = 0. If the inlet fluid is a superheated vapor, xin = 1.

### Vapor Orifice

When Modeling option is ```Vapor operating condition```, the block behavior depends on the Orifice type, Orifice parameterization, and Opening characteristic parameters.

Variable Vapor Orifice

When you set Orifice type to `Variable` and Opening characteristic to `Linear`, the block uses the input at port S to calculate the orifice opening,

`$\lambda =\epsilon \left(1-{f}_{leak}\right)\frac{\left(S-{S}_{\mathrm{min}}\right)}{\Delta S}+{f}_{leak},$`

where S is the value of the signal at port S, and Smin and ΔS are the values of the Control member position at closed orifice and Control member travel between closed and open orifice parameters, respectively.

When you set Orifice type to `Variable` and Opening characteristic to `Tabulated`, the block interpolates the orifice characteristics from the Control member position vector parameter and the input at port S.

For a variable orifice, the flow rate in the orifice depends on the parameter:

• `Linear` — The measure of flow capacity is proportional to the control signal at port S. As the control signal increases, the measure of flow capacity scales from the specified minimum to the specified maximum.

When you set to `Cv flow coefficient` or ```Kv flow coefficient```, the block treats the parameter as a constant independent of the control signal.

• `Tabulated` — The block calculates the measure of flow capacity as a function of the control signal at port S. This function uses a one-dimensional lookup table.

When you set to `Cv flow coefficient` or ```Kv flow coefficient```, the block treats the parameter as a function of the control signal.

Cv Flow Coefficient Parameterization

When you set Orifice parametrization to ```Cv flow coefficient```, the mass flow rate is

`$\stackrel{˙}{m}={C}_{v}{N}_{6}Y\sqrt{\frac{\left({p}_{in}-{p}_{out}\right)}{{v}_{in}}},$`

where:

• Cv is the flow coefficient.

• N6 is a constant equal to 27.3 when mass flow rate is in kg/hr, pressure is in bar, and density is in kg/m3.

• Y is the expansion factor.

• pin is the inlet pressure.

• pout is the outlet pressure.

• vin is the inlet specific volume.

The expansion factor is

`$Y=1-\frac{{p}_{in}-{p}_{out}}{3{p}_{in}{F}_{\gamma }{x}_{T}},$`

where:

• Fγ is the ratio of the isentropic exponent to 1.4.

• xT is the value of the xT pressure differential ratio factor at choked flow parameter.

The block smoothly transitions to a linearized form of the equation when the pressure ratio, ${p}_{out}/{p}_{in}$, rises above the value of the Laminar flow pressure ratio parameter, Blam,

`$\stackrel{˙}{m}={C}_{v}{N}_{6}{Y}_{lam}\sqrt{\frac{1}{{p}_{avg}\left(1-{B}_{lam}\right){v}_{avg}}}\left({p}_{in}-{p}_{out}\right),$`

where:

`${Y}_{lam}=1-\frac{1-{B}_{lam}}{3{F}_{\gamma }{x}_{T}}.$`

When the pressure ratio, ${p}_{out}/{p}_{in}$, falls below $1-{F}_{\gamma }{x}_{T}$, the orifice becomes choked and the block uses the equation

`$\stackrel{˙}{m}=\frac{2}{3}{C}_{v}{N}_{6}\sqrt{\frac{{F}_{\gamma }{x}_{T}{p}_{in}}{{v}_{in}}}.$`
Kv Flow Coefficient Parameterization

When you set Orifice parametrization to ```Kv flow coefficient```, the block uses the same equations as the `Cv flow coefficient` parametrization, but replaces Cv with Kv using the relation ${K}_{v}=0.865{C}_{v}$.

Vapor Orifice Area Parameterization

When you set Orifice parametrization to `Orifice area`, the mass flow rate is

`$\stackrel{˙}{m}={C}_{d}{A}_{orifice}\sqrt{\frac{2\gamma }{\gamma -1}{p}_{in}\frac{1}{{v}_{in}}{\left(\frac{{p}_{out}}{{p}_{in}}\right)}^{\frac{2}{\gamma }}\left[\frac{1-{\left(\frac{{p}_{out}}{{p}_{in}}\right)}^{\frac{\gamma -1}{\gamma }}}{1-{\left(\frac{{A}_{orifice}}{{A}_{port}}\right)}^{2}{\left(\frac{{p}_{out}}{{p}_{in}}\right)}^{\frac{2}{\gamma }}}\right]},$`

where:

• Cd is the value of the Discharge coefficient parameter.

• γ is the isentropic exponent.

The block smoothly transitions to a linearized form of the equation when the pressure ratio, ${p}_{out}/{p}_{in}$, rises above the value of the Laminar flow pressure ratio parameter, Blam,

`$\stackrel{˙}{m}={C}_{d}{A}_{orifice}\sqrt{\frac{2\gamma }{\gamma -1}{p}_{avg}^{\frac{2-\gamma }{\gamma }}\frac{1}{{v}_{avg}}{B}_{lam}^{\frac{2}{\gamma }}\left[\frac{1-\text{\hspace{0.17em}}{B}_{lam}^{\frac{\gamma -1}{\gamma }}}{1-{\left(\frac{{A}_{orifice}}{{A}_{port}}\right)}^{2}{B}_{lam}^{\frac{2}{\gamma }}}\right]}\left(\frac{{p}_{in}^{\frac{\gamma -1}{\gamma }}-{p}_{out}^{\frac{\gamma -1}{\gamma }}}{1-{B}_{lam}^{\frac{\gamma -1}{\gamma }}}\right).$`

When the pressure ratio, ${p}_{out}/{p}_{in}$, falls below${\left(\frac{2}{\gamma +1}\right)}^{\frac{\gamma }{\gamma -1}}$ , the orifice becomes choked and the block uses the equation

`$\stackrel{˙}{m}={C}_{d}{A}_{orifice}\sqrt{\frac{2\gamma }{\gamma +1}{p}_{in}\frac{1}{{v}_{in}}\frac{1}{{\left(\frac{\gamma +1}{2}\right)}^{\frac{2}{\gamma -1}}-{\left(\frac{{A}_{orifice}}{{A}_{port}}\right)}^{2}}}.$`

### Mass Balance

Mass is conserved in the orifice,

`${\stackrel{˙}{m}}_{A}+{\stackrel{˙}{m}}_{B}=0,$`

where:

• ${\stackrel{˙}{m}}_{A}$ is the mass flow rate at port A.

• ${\stackrel{˙}{m}}_{B}$ is the mass flow rate at port B.

### Energy Balance

Energy is conserved in the orifice,

`${\Phi }_{A}+{\Phi }_{B}=0,$`

where:

• ΦA is the energy flow at port A.

• ΦB is the energy flow at port B.

### Assumptions and Limitations

• There is no heat exchange between the valve and the environment.

• When Modeling option is ```Liquid operating condition```, the results may not be accurate outside of the subcooled liquid region. When Modeling option is ```Vapor operating condition```, the results may not be accurate outside of the superheated vapor region. To model an orifice in a liquid-vapor mixture, set Modeling option to ```Liquid operating condition```.

## Ports

### Conserving

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Two-phase fluid conserving port associated with the fluid entry or exit port.

Two-phase fluid conserving port associated with the fluid entry or exit port.

### Input

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Control member position that sets the orifice opening.

#### Dependencies

To enable this port, set Orifice type to `Variable`.

## Parameters

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Modeling option for the fluid phase at the orifice. Set this parameter to `Liquid operating condition` if the two-phase fluid at the block location is in a liquid state. Set this parameter to `Vapor operating condition` if the two-phase fluid at the block location is in a vapor state.

### Parameters

Type of orifice. When you set this parameter to `Variable`, the orifice area varies according to the input signal received at port S.

Method the block uses to calculate the mass flow rate from the pressure difference across the orifice or the pressure difference from the mass flow rate.

When Modeling option is ```Liquid operating condition``` and Orifice type is `Variable`, the choices for this parameter are:

• ```Linear - Area vs. control member position```

• ```Linear - Nominal mass flow rate vs. control member position```

• ```Tabulated data - Area vs. control member position```

When Modeling option is ```Liquid operating condition``` and Orifice type is `Constant`, the choices for this parameter are:

• `Orifice area`

• `Nominal mass flow rate`

When Modeling option is ```Vapor operating condition```, the choices for this parameter are:

• `Cv flow coefficient`

• `Kv flow coefficient`

• `Orifice area`

Typical, rated, or design mass flow rate through a constant orifice.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition`, Orifice type to `Constant`, and Orifice parameterization to ```Nominal mass flow rate```.

Typical, rated, or design pressure drop through a constant orifice.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition`, Orifice type to `Constant`, and Orifice parameterization to ```Nominal mass flow rate```.

Method of determining the inlet fluid state. The block determines the orifice nominal inlet specific volume from the tabulated fluid properties data based on the value of the Nominal inlet pressure parameter and the setting of the Nominal inlet condition specification parameter.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition` and either:

• Orifice type to `Constant` and Orifice parameterization to ```Nominal mass flow rate```.

• Orifice type to `Variable` and Orifice parameterization to ```Linear - Nominal mass flow rate vs. control member position```.

Inlet pressure in nominal conditions. The block determines the inlet specific volume from the tabulated fluid properties data based on the value of the Nominal inlet pressure parameter and the setting of the Nominal inlet condition specification parameter.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition` and either:

• Orifice type to `Constant` and Orifice parameterization to ```Nominal mass flow rate```.

• Orifice type to `Variable` and Orifice parameterization to ```Linear - Nominal mass flow rate vs. control member position```.

Inlet fluid temperature in nominal operating conditions.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition` and either:

• Orifice type to `Constant`, Orifice parameterization to `Nominal mass flow rate`, and Nominal inlet condition specification to `Temperature`.

• Orifice type to `Variable`, Orifice parameterization to ```Linear - Nominal mass flow rate vs. control member position```, and Nominal inlet condition specification to `Temperature`.

Inlet mixture vapor quality by mass fraction in nominal operating conditions. A value of `0` means that the inlet fluid is subcooled liquid. A value of `1` means that the inlet fluid is superheated vapor.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition` and either:

• Orifice type to `Constant`, Orifice parameterization to `Nominal mass flow rate`, and Nominal inlet condition specification to ```Vapor quality```.

• Orifice type to `Variable`, Orifice parameterization to ```Linear - Nominal mass flow rate vs. control member position```, and Nominal inlet condition specification to ```Vapor quality```.

Inlet mixture volume fraction in nominal operating conditions. A value of `0` means that the inlet fluid is subcooled liquid. A value of `1` means that the inlet fluid is superheated vapor.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition` and either:

• Orifice type to `Constant`, Orifice parameterization to `Nominal mass flow rate`, and Nominal inlet condition specification to ```Vapor void fraction```.

• Orifice type to `Variable`, Orifice parameterization to ```Linear - Nominal mass flow rate vs. control member position```, and Nominal inlet condition specification to ```Vapor void fraction```.

Inlet specific enthalpy in nominal operating conditions.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition` and either:

• Orifice type to `Constant`, Orifice parameterization to `Nominal mass flow rate`, and Nominal inlet condition specification to ```Specific enthalpy```.

• Orifice type to `Variable`, Orifice parameterization to ```Linear - Nominal mass flow rate vs. control member position```, and Nominal inlet condition specification to ```Specific enthalpy```.

Inlet specific internal energy in nominal operating conditions.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition` and either:

• Orifice type to `Constant`, Orifice parameterization to `Nominal mass flow rate`, and Nominal inlet condition specification to ```Specific internal energy```.

• Orifice type to `Variable`, Orifice parameterization to ```Linear - Nominal mass flow rate vs. control member position```, and Nominal inlet condition specification to ```Specific internal energy```.

Cross-sectional area of the orifice opening.

#### Dependencies

To enable this parameter, set Orifice type to `Constant` and Orifice parameterization to ```Orifice area```.

Control member offset, or the value at S when the orifice is fully closed.

#### Dependencies

To enable this parameter, set either:

• Modeling option to ```Liquid operating condition```, Orifice type to `Variable`, and Orifice parameterization to ```Linear – Nominal mass flow rate vs. control member position``` or ```Linear – Area vs. control member position```.

• Modeling option to ```Vapor operating condition```, Orifice type to `Variable`, and Opening characteristic to `Linear`.

Distance the control member travels between a closed and open orifice. When you set Opening orientation to ```Positive control member displacement opens orifice```, the orifice is fully open at the sum of the Control member position at closed orifice and Control member travel between closed and open orifice parameters. When you set Opening orientation to ```Negative control member displacement opens orifice```, the orifice is fully open at the difference between the Control member position at closed orifice and Control member travel between closed and open orifice parameters.

#### Dependencies

To enable this parameter, set either:

• Modeling option to ```Liquid operating condition```, Orifice type to `Variable`, and Orifice parameterization to ```Linear – Nominal mass flow rate vs. control member position``` or ```Linear – Area vs. control member position```.

• Modeling option to ```Vapor operating condition```, Orifice type to `Variable`, and Opening characteristic to `Linear`.

Direction of the member displacement that opens the variable orifice. A positive orientation means that an increase in the signal at S opens the orifice. A negative orientation means that a decrease in the signal at S opens the orifice.

#### Dependencies

To enable this parameter, set either:

• Modeling option to ```Liquid operating condition```, Orifice type to `Variable`, and Orifice parameterization to ```Linear – Nominal mass flow rate vs. control member position``` or ```Linear – Area vs. control member position```.

• Modeling option to ```Vapor operating condition```, Orifice type to `Variable`, and Opening characteristic to `Linear`.

Mass flow rate through a fully open orifice under typical, design, or rated conditions.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition`, Orifice type to `Variable`, and Orifice parameterization to ```Linear – Nominal mass flow rate vs. control member position```.

Pressure drop over a fully open orifice under typical, design, or rated conditions.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition`, Orifice type to `Variable`, and Orifice parameterization to ```Linear – Nominal mass flow rate vs. control member position```.

Orifice area when it is fully open.

#### Dependencies

To enable this parameter, set either:

• Modeling option to ```Liquid operating condition```, Orifice type to `Variable`, and Orifice parameterization to ```Linear – Area vs. control member position```.

• Modeling option to ```Vapor operating condition```, Orifice type to `Variable`, Orifice parameterization to `Orifice area`, and Opening characteristic to `Linear`.

Vector of control member positions for the tabulated orifice parameterizations. The vector elements correspond one-to-one to the values in the Orifice area vector, Cv flow coefficient vector, or Kv flow coefficient vector parameters.

#### Dependencies

To enable this parameter, set Orifice type to `Variable` and either

• Modeling option to ```Liquid operating condition``` and Orifice parameterization to ```Tabulated data - Area vs. control member position```.

• Modeling option to `Vapor operating condition` and Opening characteristic to `Tabulated`.

Vector of orifice area values for the tabulated parameterization of the orifice area. The values in this vector correspond one-to-one with the elements in the Control member position vector parameter.

#### Dependencies

To enable this parameter, set either

• Modeling option to ```Liquid operating condition```, Orifice type to `Variable`, and Orifice parameterization to ```Tabulated data - Area vs. control member position```.

• Modeling option to ```Vapor operating condition```, Orifice type to `Variable`, Orifice parameterization to `Orifice area`, and Opening characteristic to `Tabulated`.

Ratio of actual flow rate to ideal flow rate. This parameter accounts for real-world losses that are not captured in the orifice equation.

#### Dependencies

To enable this parameter, set either:

• Orifice type to `Constant` and Orifice parameterization to `Orifice area`.

• Modeling option to ```Liquid operating condition```, Orifice type to `Variable` and Orifice parameterization to either ```Linear - Area vs. control member position``` or ```Tabulated data - Area vs. control member position```.

• Modeling option to ```Vapor operating condition```, Orifice type to `Variable` and Orifice parameterization to `Orifice area`.

Whether to account for the small rise in pressure after the pressure drop from the inlet to the orifice hole. When the fluid jet exits the orifice hole, it dissipates and expands to fill the port area, which causes this small pressure rise. The block does not model this pressure increase when you clear the Pressure recovery check box.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition` and either:

• Orifice type to `Variable` and Orifice parameterization to either ```Linear - Area vs. control member position``` or ```Tabulated data - Area vs. control member position```.

• Orifice type to `Constant` and Orifice parameterization to `Orifice area`.

Method by which to convert the control signal specified at port S to the chosen measure of flow capacity.

#### Dependencies

To enable this parameter, set Modeling option to `Vapor operating condition` and Orifice type to `Variable`.

Value of the constant Cv flow coefficient. This parameter measures the ease with which the vapor traverses the resistive element when driven by a pressure differential.

#### Dependencies

To enable this parameter, set Modeling option to `Vapor operating condition`, Orifice type to `Constant`, and Orifice parameterization to ```Cv flow coefficient```.

Value of the Cv flow coefficient when the orifice is fully open and the area available for flow is at a maximum. This parameter measures the ease with which the vapor traverses the resistive element when driven by a pressure differential.

#### Dependencies

To enable this parameter, set Modeling option to `Vapor operating condition`, Orifice type to `Variable`, Orifice parameterization to ```Cv flow coefficient```, and Opening characteristic to `Linear`.

Vector of Cv flow coefficients. Each coefficient corresponds to a value in the Control member position vector parameter. This parameter measures the ease with which the vapor traverses the resistive element when driven by a pressure differential. The size of the vector must be the same as the Control member position vector parameter.

#### Dependencies

To enable this parameter, set Modeling option to `Vapor operating condition`, Orifice type to `Variable`, Orifice parameterization to ```Cv flow coefficient```, and Opening characteristic to `Tabulated`.

Value of the constant Kv flow coefficient. This parameter measures the ease with which the vapor traverses the resistive element when driven by a pressure differential.

#### Dependencies

To enable this parameter, set Modeling option to `Vapor operating condition`, Orifice type to `Constant`, and Orifice parameterization to ```Kv flow coefficient```.

Value of the Kv flow coefficient when the orifice is fully open and the area available for flow is at a maximum. This parameter measures the ease with which the vapor traverses the resistive element when driven by a pressure differential.

#### Dependencies

To enable this parameter, set Modeling option to `Vapor operating condition`, Orifice type to `Variable`, Orifice parameterization to ```Kv flow coefficient```, and Opening characteristic to `Linear`.

Vector of Kv flow coefficients. Each coefficient corresponds to a value in the Control member position vector parameter. This parameter measures the ease with which the vapor traverses the resistive element when driven by a pressure differential. The size of the vector must be the same as the Control member position vector parameter.

#### Dependencies

To enable this parameter, set Modeling option to `Vapor operating condition`, Orifice type to `Variable`, Orifice parameterization to ```Kv flow coefficient```, and Opening characteristic to `Tabulated`.

Ratio between the inlet pressure, pin, and the outlet pressure, pout, defined as $\left({p}_{in}-{p}_{out}\right)/{p}_{in}$ where choking first occurs.

#### Dependencies

To enable this parameter, Modeling option to ```Vapor operating condition``` and Orifice parameterization to ```Cv flow coefficient``` or ```Kv flow coefficient```.

Ratio of the flow rate of the orifice when it is closed to when it is open.

#### Dependencies

To enable this parameter, set Orifice type to `Variable` and any combination of other parameters, except when:

• Modeling option is ```Liquid operating condition``` and Orifice parameterization is ```Tabulated data - Area vs. control member position```.

• Modeling option is `Vapor operating condition` and Opening characteristic is `Tabulated`.

Continuous smoothing factor that introduces a layer of gradual change to the flow response when the orifice is in near-open or near-closed positions. Set this parameter to a nonzero value less than one to increase the stability of your simulation in these regions.

#### Dependencies

To enable this parameter, set Orifice type to `Variable` and any combination of other parameters, except when:

• Modeling option is ```Liquid operating condition``` and Orifice parameterization is ```Tabulated data - Area vs. control member position```.

• Modeling option is `Vapor operating condition` and Opening characteristic is `Tabulated`.

Time lag for liquid-vapor mixtures in computing the fluid specific volume.

#### Dependencies

To enable this parameter, set Modeling option to `Liquid operating condition`.

Ratio of the orifice outlet pressure to orifice inlet pressure at which the fluid transitions between the laminar and turbulent regimes. The pressure loss corresponds to the mass flow rate linearly in laminar flows and quadratically in turbulent flows.

Area of the orifice ports A and B.

## References

[1] ISO 6358-3. "Pneumatic fluid power – Determination of flow-rate characteristics of components using compressible fluids – Part 3: Method for calculating steady-state flow rate characteristics of systems". 2014.

[2] IEC 60534-2-3. "Industrial-process control valves – Part 2-3: Flow capacity – Test procedures". 2015.

[3] ANSI/ISA-75.01.01. "Industrial-Process Control Valves – Part 2-1: Flow capacity – Sizing equations for fluid flow underinstalled conditions". 2012.

[4] P. Beater. Pneumatic Drives. Springer-Verlag Berlin Heidelberg. 2007.

## Version History

Introduced in R2021a

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