Engee documentation

Orifice (IL)

An opening of constant or variable area in an isothermal liquid network.

Variable Orifice (IL)
variable orifice (il)

Orifice (IL)
orifice (il)

Description

The Orifice (IL) block simulates flow through a local restriction with a constant or variable opening area. For variable openings, a control connected to the S port sets the opening position. The opening area is varied linearly or by using a look-up table.

local restriction (il) 1 s

The block equations determine the mass flow rate through the pressure difference between ports A and B:

This mass conservation equation implies an increase in velocity when the area decreases and a decrease in velocity when the flow goes into a larger area. According to Bernoulli’s principle, this change in velocity results in an area of reduced pressure at the port and increased pressure in the expansion area. The resulting pressure increase, called pressure recovery, depends on the orifice flow coefficient and the ratio of orifice to port area.

Port constants

For constant orifices, the port area, , does not change during the simulation.

Usage of the Orifice type parameters Constant

The block calculates the mass flow rate as:

ρρ ,

where

  • - is the Discharge coefficient;

  • - instantaneous open orifice area;

  • - cross-sectional area of ports A and B;

  • ρ - average density of the liquid.

Pressure losses and are calculated in the same way for fixed and variable orifices.

This approximation for and the Local Restriction (IL) unit is the same.

Usage of Tabulated data for the Orifice parameterization - volumetric flow rate vs. pressure drop

The volumetric flow rate is determined based on tabulated pressure drop values that you can provide. If you provide only non-negative values for the volumetric flow rate and pressure drop vectors, the block extrapolates the table to negative values. The volumetric flow rate is interpolated from this extended table.

If the Volumetric flow rate vector and Pressure drop vector parameters contain both negative and positive values but do not contain 0, the block inserts the origin into the vectors to ensure that the valve does not have a non-zero flow rate at a pressure drop of 0, which is unphysical.

Variable orifices

For variable orifices, setting the Opening orientation parameters to Positive control member displacement opens orifice opens the orifice when the signal at port S is positive, and setting the Negative control member displacement opens orifice opens the orifice when the signal at port S is negative. If the signal is positive in both cases, the opening of the orifice is determined by the magnitude of the signal.

Usage of Linear - Area vs. control member position for Orifice parameterization

The orifice area depends on the control member position and the ratio of the orifice area to the maximum control member position:

ε

where

  • - is the position of the control member when the orifice is fully closed;

  • - the value of the Control member travel between closed and open orifice parameters;

  • - value of parameter Maximum orifice area;

  • - value of parameter Leakage area;

  • ε - value of the Opening orientation parameters.

When the orifice is in the nearly open or nearly closed position in the linear parameterization, you can maintain the numerical stability of the simulation by adjusting the Smoothing factor parameter. If the Smoothing factor parameters are not zero, the block smoothly saturates the hole area between and .

The volumetric flow rate is determined from the pressure-flow equation:

ρ ,

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

Usage of Tabulated data - Area vs. control member position Parameterization value for Orifice parameterization

With usage of the parameterization Tabulated data - Area vs. control member position, the bore area is interpolated from the tabulated bore area and control member position that you can provide. As with the `Linear - Area vs. control member position' parameterization, the volume flow rate is determined using the pressure-flow equation:

ρ ,

where

  • - is:

    • - The last element of the Orifice area vector if the hole is larger than the maximum specified hole;

    • - the first element of the Orifice area vector if the hole is smaller than the minimum specified hole;

    • if the calculated area is between the limits of the Orifice area vector;

  • - function of the position of the control element arriving at the S port. The block queries between data points using linear interpolation and uses nearest extrapolation for points outside the table boundaries.

Usage of the Orifice parameterization value Tabulated data - Volumetric flow rate vs. control member position and pressure drop

The Tabulated data - Volumetric flow rate vs. control member position and pressure drop parameterization interpolates the volumetric flow rate directly from the user supplied volumetric flow rate table, which is based on the control member position and pressure drop across the orifice. The block queries between data points using linear interpolation and uses linear extrapolation for points outside the table boundaries.

These data points may include negative differential pressures and negative opening values. If a negative pressure drop is included in the data set, the volumetric flow rate will change direction. However, for negative openings, the flow rate will remain unchanged.

If the Pressure drop vector parameter, dp does not contain 0 and the Volumetric flow rate table parameter, q(s,dp) is the corresponding column of zeros, the block inserts them so that the valve does not have a non-zero flow rate when the pressure drop is 0, which is unphysical.

Pressure loss

Pressure loss describes the reduction in pressure in a valve due to a reduction in area. The term pressure loss, , is calculated as:

Pressure recovery describes a positive change in valve pressure due to an increase in area. If you do not want to record this pressure increase, uncheck the Pressure recovery box. In this case will be set to 1.

Critical pressure

The critical pressure drop is the pressure drop associated with the critical Reynolds number, , which is the transition point between laminar and turbulent fluid flow:

πρν

Ports

Input

S - movement of the control element
scalar

Input port of the control element movement that specifies the opening of the hole.

Non-directional

A - isothermal liquid port
isothermal liquid

Isothermal liquid port, corresponds to the inlet or outlet of the port. This unit has no internal directionality.

B - isothermal liquid port
`isothermal liquid'.

Isothermal liquid port, corresponds to the inlet or outlet of the port. This unit has no internal directionality.

Parameters

Orifice type - hole type
Variable (by default) | Constant

Hole type defined by the area of the hole. When set to Variable, the hole area varies depending on the input signal to port S.

Orifice parameterization is the method of calculating the hole area
Orifice Area (By default) | Tabulated data − volumetric flow rate vs. pressure drop | Linear - area vs. control member position | Tabulated data - Area vs. control member position | Tabulated data - Volumetric flow rate vs. control member position and pressure drop

Method for calculating orifice area in modelling.

If the Orifice type parameter is set to Constant, there are two parameterization options:

  • Orifice Area. The assigned area is not changed during simulation.

  • Tabulated data - Volumetric flow rate vs. pressure drop. The area remains constant, but the volumetric flow rate through the orifice may vary. This value is interpolated directly from the Volumetric flow rate vector and Pressure drop vector parameters.

If Orifice type is set to Variable, there are three parameterization options:

  • Linear - Area vs. control member position. The area is determined by the linear dependence on the position of the control member in relation to a fully open or fully closed orifice. The position is set by a variable signal at the S port.

  • Tabulated data - Area vs. control member position. The orifice area is interpolated from the Control member position vector and Orifice area vector based on the position of the control element received at the S port.

  • Tabulated data - Volumetric flow rate vs. control member position and pressure drop. The volumetric flow rate is directly interpolated from user supplied parameters Control member position vector, Pressure drop vector and Volumetric flow rate table based on the control member position obtained through port S and pressure drop through ports A and B.

Orifice area - orifice area
1e-3 m² (by default) | Positive scalar

The cross-sectional area of the hole.

Dependencies

To use this parameter, set the Orifice type parameters to Constant and the Orifice parameterization parameters to Orifice area.

Pressure drop vector - vector of pressure drop values for tabular parameterization
[-4, −3, −2, −1, −.5, 0, .5, 1, 2, 3, 4] MPa (by default) | vector

Vector of differential pressure values for the tabular parameterization of the volume flow. The values in this vector correspond one-to-one to the values in the Pressure drop vector parameters. The values of the pressure drop vector are listed in ascending order. The volumetric flow rate is interpolated directly from the Volumetric flow rate vector, which depends on the Pressure drop vector parameters.

Dependencies

To use this parameter, set the Orifice type parameter to `Constant' and the Orifice parameterization parameter to `Tabulated data - Volumetric flow rate vs. pressure drop'.

The Volumetric flow rate vector is a vector of volumetric flow rate values
[-2.44, −2.12, −1.68, −1.22, −.84, 0, .85, 1.21, 1.7, 2.09, 2.41] .* 1e-3 m³/s (by default) | vector 1 to n

Vector of volumetric flow rate values for the tabular parameterization of the volumetric flow rate. The values in this vector correspond one-to-one to the values in the Pressure drop vector. The volumetric flow rate is interpolated directly from the Volumetric flow rate vector, which depends on the Pressure drop vector parameters.

Dependencies

To use this parameter, set the Orifice type parameters to `Constant' and the Orifice parameterization parameters to `Tabulated data - Volumetric flow rate vs. pressure drop'.

Control member position at closed orifice - control member offset
0 m (by default) | scalar.

Initial offset of the control member when the variable orifice is fully closed.

Dependencies

To use this parameter, set the Orifice type parameters to Variable.

Control member travel between closed and open orifice - maximum travel of the control member
5e-3 m (by default) | positive scalar.

The maximum distance the control element travels between closed and open orifices. The orifice is fully open at the sum of the position of the control element when the orifice is closed and the travel of the control element between the closed and open orifice.

Dependencies

To use this parameter, set the Orifice type parameter to `Variable' and the Orifice parameterization parameter to `Linear - Area vs. control member position'.

Maximum orifice area - maximum orifice opening area
1e-4 m² (by default) | positive scalar.

Maximum orifice area during the simulation. With usage of Tabulated data - Area vs. control member position, the maximum opening area is the last element of the Orifice area vector.

Dependencies

To use this parameter, set the Orifice type parameter to Variable and the Orifice parameterization parameter to Linear - Area vs. control member position.

Leakage area is the area of the gap between the holes in the fully closed position
1e-10 m² (by default) | positive scalar.

The sum of all clearances when the valve is in the fully closed position. Any area smaller than this value is maintained at the specified leakage area. This parameter contributes to numerical stability by maintaining flow continuity.

Dependencies

To use this parameter, set the Orifice type parameters to `Variable' and the Orifice parameterization parameters to `Linear - Area vs. control member position'.

The Control member position vector is a vector of control member positions
[0, .002, .004, .007, .017] m (by default) | vector 1 to n.

Control element position vector for the tabular parameterization of the volumetric flow rate. The one-to-one control element position vector corresponds to the Orifice area vector. The values are listed in ascending order and the first element must be equal to 0. Linear interpolation is used between the data points in the table.

Dependencies

To use this parameter, set the Orifice type parameter to Variable and the Orifice parameterization parameter to Tabulated data - Area vs. control member position.

The Orifice area vector is a vector of values for the opening area of the orifice
[1e-09, 2.0352e-07, 4.0736e-05, .00011438, .00034356] m² (by default) | ` vector 1 to n`.

Vector of hole area values for the tabular parameterization of the hole area. The values in this vector are related one-to-one with the elements in the Control member position vector. If the vector is increasing, the first element of this vector is the leakage area of the hole and the last element is the maximum hole area. If the vector is decreasing, the first element of this vector is the maximum opening area and the last element is the leakage area. The opening area of the hole is interpolated from the hole area vector, which depends on the Control member position vector.

Dependencies

To use this parameter, set the Orifice type parameter to `Variable' and the Orifice parameterization parameter to `Tabulated data - Area vs. control member position'.

Cross-sectional area at ports A and B - area at the inlet or outlet of the hole
inf (by default) | positive scalar

The cross-sectional area at the inlet and outlet of holes A and B. This area is used in the pressure flow velocity equation that determines the mass flow rate through the orifice.

Dependencies

To use this parameter, set:

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

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

Opening orientation - direction of movement of the opening member
Positive control member displacement opens orifice (by default) | Negative control member displacement opens orifice.

The direction of movement of the element that opens the variable orifice. Positive orientation means that a positive signal at S opens the orifice. Negative orientation means that a negative signal at S opens the hole.

Dependencies

To use this parameter, set the Orifice type parameter to Variable.

Discharge coefficient - discharge coefficient
0.64 (by default) | positive scalar in the range [0,1].

Correction factor to account for discharge losses in theoretical flows.

Dependencies

To use this parameters, set:

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

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

Critical Reynolds number - upper limit of Reynolds number for laminar flow
150 (By default) | positive scalar

Upper limit of Reynolds number for laminar flow through the orifice.

Dependencies

To use this parameter, set:

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

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

Smoothing factor - numerical smoothing factor
0.01 (by default) | positive scalar in the range [0,1]

A continuous smoothing factor that introduces a layer of gradual change in the flow response when the orifice is in the nearly open or nearly closed position. Set a non-zero value less than one to increase the stability of the simulation in these modes.

Pressure recovery - whether to take into account the pressure rise when the region expands
off (By default) | on

Whether to take into account the pressure rise when fluid flows from a smaller cross-sectional area to a larger cross-sectional area.

If Pressure recovery is unchecked, this pressure increase is not taken into account.

Dependencies

To use this parameter, set:

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

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

Control member position vector, s - control member position vector
[0, .002, .004, .007, .017] m (by default) | ` vector 1 to m`

Control element position vector for the tabular parameterization of the volumetric flow rate. The one-to-one position vector of the controls corresponds to the pressure drop vector Pressure drop vector, dp, for the two-dimensional dependence of the volumetric flow rate table Volumetric flow rate table, q(s,dp). A positive offset corresponds to valve opening. The values are listed in ascending order and the first element must be 0. Linear interpolation is used between the data points in the table.

Dependencies

To use this parameter, set the Orifice type parameter to `Variable' and the Orifice parameterization parameter to `Tabulated data - Volumetric flow rate vs. control member position and pressure drop'.

Pressure drop vector is a vector of pressure drop values
[.3, .5, .7] MPa (by default) | ` vector 1 to m`.

Vector of differential pressure values for the tabular parameterization of the volumetric flow rate. The one-to-one differential pressure vector corresponds to the Control member position vector, s for the two-dimensional dependence of the volumetric flow rate table Volumetric flow rate table, q(s,dp). The values are listed in ascending order and must be greater than 0. Linear interpolation is used between the table data points.

Dependencies

To use this parameter, set the Orifice type parameter to `Variable' and the Orifice parameterization parameter to `Tabulated data - Volumetric flow rate vs. control member position and pressure drop'.

The Volumetric flow rate table is an array of volumetric flow rate values
[1.7e-05, 2e-05, 2.6e-05; .0035, .0045, .0053; .7, .9, 1.06; 1.96, 2.5, 3; 6, 7.7, 9.13] .* 1e-3 m³/s (by default) | matrix m by n.

A matrix of m by n volume flow rates based on independent values of pressure drop and control element position. m and n are the dimensions of the corresponding vectors:

  • m - number of elements in the pressure drop vector Pressure drop vector, dp.

  • n - number of elements in the control member position vector Control member position vector, s.

Dependencies

To use this parameter, set the Orifice type parameter to Variable and the Orifice parameterization parameter to Tabulated data - Volumetric flow rate vs. control member position and pressure drop.