Pressure Relief Valve (TL)

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Safety valve in the thermal liquid network.

blockType: EngeeFluids.ThermalLiquid.Valves.PressureControl.Relief

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/Physical Modeling/Fluids/Thermal Liquid/Valves & Orifices/Pressure Control Valves/Pressure Relief Valve (TL)

Description

The Pressure Relief Valve (TL) unit is a pressure relief valve for depressurising the thermal liquid network. The valve is closed when the pressure is less than the set pressure value. When the pressure reaches or exceeds the set pressure value, the valve opens. The set pressure is either the threshold pressure drop across the valve between ports A and B or between port A and atmospheric pressure. A control pressure greater than the set pressure causes the valve to gradually open, allowing excess pressure in the fluid network to be relieved.

Pressure control

If the parameters Opening parameterization are set to . Linear - Area vs. pressure, the normalised pressure determines the opening area. The normalised pressure is defined as:

where

- is the control pressure. If the parameter Pressure control specification is set to . Pressure differential, then the control pressure is . If the parameter Pressure control specification is set to , the control pressure is the difference between the pressure at port A and the atmospheric pressure; where is the control pressure. Pressure at port A, the control pressure is the difference between the pressure in the A port and the atmospheric pressure;
- set pressure. If the parameter Pressure control specification is set to , the control pressure is the difference between the pressure in the port A and the atmospheric pressure; the setting pressure. Pressure differential, then is the value of the Set pressure differential parameters. If the parameter Pressure control specification is set to , then is the value of the parameter Set pressure differential. `Pressure at port A`then is the value of the parameter Set pressure (gauge);
- maximum pressure control range, defined as , where is the value of the parameter Pressure regulation range.

Parameterization: pressure dependent area

If the parameters Opening parameterization are set to the value of Linear - Area vs. pressure or Tabulated data - Area vs. pressure, the mass flow rate is

where

- flow coefficient, the value of parameters Discharge coefficient;
- is the instantaneous opening area of the valve;
- parameter value Cross-sectional area at ports A and B;
- average density of the liquid;
- pressure drop.

Critical pressure drop is the pressure drop determined from the value of the critical Reynolds number , given by the parameter Critical Reynolds number, the transition point of the regime between laminar and turbulent flow. The block calculates the critical pressure drop as:

where is the dynamic viscosity of thermal liquid.

The pressure loss describes the pressure drop in the valve due to the reduced valve area and is calculated as:

Pressure recovery allows the positive pressure change in the valve due to an increase in area to be taken into account. To disregard the pressure recovery, uncheck the box Pressure recovery. In this case the pressure loss .

If the parameters Opening parameterization are set to . Linear - Area vs. pressure, the opening area is:

where

- is the value of the parameters Leakage area;
- the value of the parameters Maximum opening area.

This figure shows how the block controls the valve opening area using linear parameterization.

pressure compensator valve il 2

When the valve is in the nearly open or nearly closed position in the linear parameterization, it is possible to maintain numerical stability in the simulation by adjusting the parameter Smoothing factor. If the parameter Smoothing factor is not zero, a smooth change of the control pressure between and is ensured.

If the parameter Opening parameterization is set to the value of Tabulated data - Area vs. pressure, the block calculates the opening area as

where

;
- the value of the Pressure differential vector or Opening pressure (gauge) vector parameter, depending on the value of the parameter Pressure control specification;
- is the change in internal pressure at which the valve starts to close when ;
- value of the Opening area vector parameters.

This figure shows how the block controls the valve opening area using tabular parameterization.

pressure compensator valve il 4

Parametrization: Volume flow rate as a function of pressure

If the parameters Opening parameterization are set to . Tabulated data - Volumetric flow rate vs. pressure, the valve opens according to the user-supplied tabulated volume flow rate and pressure drop between ports A and B.

The mass flow rate is defined as

where

- volume flow rate;
- average density of the liquid.

The unit calculates the relationship between mass flow rate and pressure using the relationship:

where

Opening dynamics

If the check box Opening dynamics is selected, a delay is introduced in the flow response to the modelled control pressure. The pressure becomes the dynamic control pressure . The instantaneous change in the dynamic control pressure is calculated from the Opening time constant :

By default, the check box Opening dynamics is unchecked.

Energy storage

The equation of conservation of energy in a valve is of the form:

where

- is the energy flow entering the valve through port A;
- is the energy flow entering the valve through port B.

Ports

Conserving

# A — thermal liquid port
thermal liquid

Details

Thermal liquid port, corresponds to the valve inlet.

Program usage name

inlet

# B — thermal liquid port
thermal liquid

Details

Thermal liquid port, corresponds to the valve outlet.

Program usage name

outlet

Parameters

# Opening parameterization — valve opening calculation method
Linear - Area vs. pressure | Tabulated data - Area vs. pressure | Tabulated data - Volumetric flow rate vs. pressure

Details

Valve opening modelling method. The valve opening is parameterised either linearly or using a table of values that relate area to pressure drop.

Values	`Linear - Area vs. pressure` \| `Tabulated data - Area vs. pressure` \| `Tabulated data - Volumetric flow rate vs. pressure`
Default value	`Linear - Area vs. pressure`
Program usage name	`opening_parameterization`
Evaluatable	Yes

# Pressure control specification — differential pressure used to control the valve
Pressure differential | Pressure at port A

Details

The method of setting the control pressure of the valve. If this parameter is set to a value of Pressure at port A, the unit uses only the pressure at port A to determine if the flow pressure exceeds the value of the parameter Set pressure (gauge). If this parameter is set to Pressure differential, the unit uses the Set pressure differential parameter value to determine if the pressure differential from port A to port B is out of range.

Dependencies

To use this parameter, set the parameters Opening parameterization to Linear - Area vs. pressure or Tabulated data - Area vs. pressure.

Values	`Pressure differential` \| `Pressure at port A`
Default value	`Pressure at port A`
Program usage name	`opening_pressure_type`
Evaluatable	Yes

# Set pressure (gauge) — overpressure at which the opening mechanism is triggered
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

Pressure at which the opening mechanism is actuated. The opening area remains variable over the entire pressure control range of the valve.

Dependencies

To use this parameter, set the Opening parameterization parameters to and the parameters to . Linear - Area vs. pressure`and set the Pressure control specification parameters to . `Pressure at port A or set the Opening parameterization parameters to . Tabulated data - Volumetric flow rate vs. pressure.

Units	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`0.1 MPa`
Program usage name	`p_set_gauge`
Evaluatable	Yes

# Pressure regulation range — operating pressure range of the valve
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

The working pressure range of the valve. The valve starts opening at the set pressure value and opens fully at the maximum value of the working range , where .

Dependencies

To use this parameter, set the parameters Opening parameterization to the following value Linear - Area vs. pressure.

Units	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`0.15 MPa`
Program usage name	`p_regulation_range`
Evaluatable	Yes

# Maximum opening area — fully open valve area
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2

Details

Area of the valve in the fully open position.

Dependencies

To use this parameter, set the parameters Opening parameterization to . Linear - Area vs. pressure.

Units	`m^2` \| `cm^2` \| `ft^2` \| `in^2` \| `km^2` \| `mi^2` \| `mm^2` \| `um^2` \| `yd^2`
Default value	`0.0001 m^2`
Program usage name	`max_valve_area`
Evaluatable	Yes

# Leakage area — valve clearance area in fully closed position
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2

Details

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

Dependencies

To use this parameter, set the parameter Opening parameterization to the value of Linear - Area vs. pressure.

Units	`m^2` \| `cm^2` \| `ft^2` \| `in^2` \| `km^2` \| `mi^2` \| `mm^2` \| `um^2` \| `yd^2`
Default value	`1e-10 m^2`
Program usage name	`leakage_area`
Evaluatable	Yes

# Cross-sectional area at ports A and B — area at the inlet or outlet of the valve
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2

Details

The cross-sectional area at the inlet and outlet ports A and B. This area is used when calculating the mass flow rate through the valve.

Dependencies

To use this parameter, set the parameters Opening parameterization to the value of Linear - Area vs. pressure or Tabulated data - Area vs. pressure.

Units	`m^2` \| `cm^2` \| `ft^2` \| `in^2` \| `km^2` \| `mi^2` \| `mm^2` \| `um^2` \| `yd^2`
Default value	`0.01 m^2`
Program usage name	`port_area`
Evaluatable	Yes

# Discharge coefficient — flow coefficient

Details

The correction factor is the ratio of the actual mass flow rate to the theoretical mass flow rate through the valve.

Dependencies

To use this parameter, set the parameters Opening parameterization to the value of Linear - Area vs. pressure or Tabulated data - Area vs. pressure.

Default value	`0.64`
Program usage name	`C_d`
Evaluatable	Yes

# Critical Reynolds number — upper limit of Reynolds number for laminar flow

Details

Upper Reynolds number limit for laminar flow through the valve.

Dependencies

To use this parameter, set the parameters Opening parameterization to the value of Linear - Area vs. pressure or Tabulated data - Area vs. pressure.

Default value	`150.0`
Program usage name	`Re_critical`
Evaluatable	Yes

# Smoothing factor — numerical smoothing factor

Details

The continuous smoothing factor provides a smooth opening by correcting the valve characteristic in the nearly open and nearly closed positions. Set a non-zero value less than one to increase the stability of the simulation in these modes.

Dependencies

To use this parameter, set the parameters Opening parameterization to a value less than one. Linear - Area vs. pressure or Tabulated data - Area vs. pressure.

Default value	`0.01`
Program usage name	`smoothing_factor`
Evaluatable	Yes

# Pressure recovery — taking into account the pressure rise during the expansion of the area

Details

Determines whether pressure rise is taken into account when fluid flows from a smaller cross-sectional area to a larger cross-sectional area.

Dependencies

To use this parameter, set the Opening parameterization parameters to Linear - Area vs. pressure or Tabulated data - Area vs. pressure.

Default value	`false (switched off)`
Program usage name	`pressure_recovery`
Evaluatable	Yes

# Opening dynamics — consideration of valve opening dynamics

Details

Determines whether the transient effects in the fluid system caused by valve opening should be taken into account. Checking Opening dynamics introduces a first-order lag to the valve signal pressure. The Opening time constant parameter determines the opening dynamics.

Dependencies

To use this parameter, set the parameters Opening parameterization to the value of Linear - Area vs. pressure or Tabulated data - Area vs. pressure.

Default value	`false (switched off)`
Program usage name	`opening_dynamics`
Evaluatable	Yes

# Set pressure differential — minimum pressure drop
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

Minimum pressure drop between ports A and B required to open the valve. If the differential pressure exceeds this value, the valve gradually opens until it reaches the fully open state.

Dependencies

To use this parameter, set the parameters Opening parameterization to Linear - Area vs. pressure`and set the parameters Pressure control specification to . `Pressure differential.

Units	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`0.0 MPa`
Program usage name	`delta_p_set`
Evaluatable	Yes

# Opening time constant — valve opening time constant
d | s | hr | ms | ns | us | min

Details

Time constant by which the delay in the opening dynamics is calculated.

Dependencies

To use this parameter, select the check box Opening dynamics.

Units	`d` \| `s` \| `hr` \| `ms` \| `ns` \| `us` \| `min`
Default value	`0.1 s`
Program usage name	`tau`
Evaluatable	Yes

# Pressure differential vector — differential pressure values for tabular parameterization
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

Vector of differential pressure values for tabular parameterization of the valve opening area. The elements of the vector correspond to the elements of the vector from parameter Opening area vector or from parameter Volumetric flow rate vector, depending on the selected parameterization type. The elements are listed in ascending order and must be greater than 0. Linear interpolation is used between tabulated data points.

The first element of this parameter is the pressure value at which the valve starts to open. The last element is the maximum pressure at which the valve is fully open. The difference between these two values is the pressure control range of the valve.

Dependencies

To use this parameters:

set the parameters Opening parameterization to. Tabulated data - Area vs. pressure`and set the parameters Pressure control specification to `Pressure differential.
set the Opening parameterization parameters to . Tabulated data - Volumetric flow rate vs. pressure.

Units	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`[0.2, 0.4, 0.6, 0.8, 1.0, 1.2] MPa`
Program usage name	`delta_p_vector`
Evaluatable	Yes

# Opening area vector — vector of valve opening area values for tabular parameterization
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2

Details

Vector of valve opening area values for tabular parameterization. The values in this vector correspond to the elements of the vector from the Pressure differential vector parameters. The elements are listed in ascending order and must be greater than 0. Linear interpolation is used between the tabular data points.

Dependencies

To use this parameter, set the parameter Opening parameterization to the value of Tabulated data - Area vs. pressure.

Units	`m^2` \| `cm^2` \| `ft^2` \| `in^2` \| `km^2` \| `mi^2` \| `mm^2` \| `um^2` \| `yd^2`
Default value	`[1.0e-10, 2.0e-6, 4.0e-6, 6.0e-6, 8.0e-6, 1.0e-5] m^2`
Program usage name	`valve_area_vector`
Evaluatable	Yes

# Opening pressure (gauge) vector — gauge pressure values for tabular parameterization
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

Vector of overpressure values for the tabular parameterization of the valve opening area. The elements of the vector correspond to the elements of the vector from the parameter Opening area vector. The elements are listed in ascending order and must be greater than 0. Linear interpolation is used between the tabular data points.

The first element of this parameters is the pressure value at which the valve starts to open. The last element is the maximum pressure at which the valve is fully open. The difference between these two values is the pressure control range of the valve.

Dependencies

To use this parameter, set the parameters Opening parameterization to the value of Tabulated data - Area vs. pressure`and the parameters Pressure control specification are set to `Pressure at port A.

Units	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`[0.2, 0.4, 0.6, 0.8, 1.0, 1.2] MPa`
Program usage name	`p_gauge_vector`
Evaluatable	Yes

# Volumetric flow rate vector — vector of volume flow rates for tabular parameterization
m^3/s | m^3/h | cm^3/s | mm^3/s | ft^3/s | lpm | l/s | gpm | gal/s | gal/h

Details

Vector of volume flow values for tabular parameterization. The values in this vector correspond to the elements of the vector from the Pressure differential vector parameters. The elements are listed in ascending order.

Dependencies

To use this parameter, set the parameters Opening parameterization to . Tabulated data - Volumetric flow rate vs. pressure.

Units	`m^3/s` \| `m^3/h` \| `cm^3/s` \| `mm^3/s` \| `ft^3/s` \| `lpm` \| `l/s` \| `gpm` \| `gal/s` \| `gal/h`
Default value	`[1.0e-9, 3.6e-5, 8.9e-5, 0.00015, 0.00023, 0.00031] m^3/s`
Program usage name	`Vdot_vector`
Evaluatable	Yes