/Physical Modeling/Fluids/Thermal Liquid/Valves & Orifices/Pressure Control Valves/Pressure Reducing Valve (TL)
Description
The Pressure Reducing Valve (TL) unit is a pressure reducing valve in a thermal liquid network. The valve remains open when the pressure at port B is less than the set point. When the pressure at port B reaches or exceeds the set point, the valve closes. The unit is controlled by the difference between the set pressure and the pressure at port B. The unit contains a check valve part that functions identically to the Check Valve (TL) unit when the flow is reversed.
Pressure control
Unit Pressure Reducing Valve (TL) regulates the pressure between the set pressure and the maximum pressure.
The normalised pressure controls the valve cross-sectional area when the parameters Opening parameterization are set to Linear - Area vs. pressure. The normalised pressure represents:
where
- control pressure equal to , where is the atmospheric pressure;
- setting pressure equal to , where is the value of parameters Set pressure (gauge);
- maximum pressure equal to , where is the value of the parameter Pressure regulation range.
Parametrization: area as a function of pressure
If the parameters Opening parameterization are set to Linear - Area vs. pressure or Tabulated data - Area vs. pressure, the mass flow rate through the valve is calculated as follows:
where
- is the flow coefficient, the value of the parameters Discharge coefficient;
- instantaneous valve opening area;
- parameter value Cross-sectional area at ports A and B;
- average density of the liquid;
- pressure difference in the valve .
Critical pressure drop, - pressure drop associated with the value of critical Reynolds number , set by the parameter Critical Reynolds number, which is the point of regime transition between laminar and turbulent flow regimes. The block calculates the critical pressure drop as:
where is the dynamic viscosity of thermal liquid.
The pressure loss takes into account the pressure drop in the valve due to the reduced valve area and is calculated as:
Pressure recovery describes the positive pressure change in the valve due to an increase in area. To disregard the pressure recovery, uncheck the box Pressure recovery. In this case the pressure loss .
If the parameters Opening parameterization is set to . Linear - Area vs. pressure, then the valve cross-sectional area is:
where
- is the value of parameters Leakage area;
- the value of the parameters Maximum opening area.
The figure shows the valve opening characteristics with usage of linear area parameterization.
When the valve is in the nearly open or nearly closed position with linear parameterization, it is possible to maintain numerical stability in the simulation by adjusting the parameter Smoothing factor. If the parameters Smoothing factor is non-zero, a smooth variation of the control pressure and is ensured.
If the parameter Opening parameterization is set to a value of Tabulated data - Area vs. pressure, then the block calculates the opening area as:
where
- control pressure;
;
- is the value of the parameter Pressure at port B (gauge) vector;
- the internal pressure offset at which the valve starts to close when ;
- value of the parameter Opening area vector.
The values and are the first and last elements of the Opening area vector parameters, respectively.
The figure shows the valve opening characteristics with usage of the tabular parameterization.
If the parameter Opening parameterization is set to . Tabulated data - Volumetric flow rate vs. pressure, the valve opening is determined according to the user-supplied tabulated volume flow rate and pressure drop between ports A and B. The mass flow rate through the valve is calculated as follows:
where
- volume flow rate;
- average density of the liquid;
The unit calculates the relationship between mass flow rate and pressure using:
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 energy conservation equation for the valve is as follows:
where
- is the energy flow entering the valve through port A;
- is the energy flow entering the valve through port B.
Thermal liquid port, corresponds to valve inlet B.
Program usage name
outlet
Parameters
Parameters
#Opening parameterization —
method of calculating valve opening or closing
Linear - Area vs. pressure | Tabulated data - Area vs. pressure | Tabulated data - Volumetric flow rate vs. pressure
Details
Method for modelling the opening of the valve. Options for selection:
Linear - Area vs. pressure or Tabulated data - Area vs. pressure - valve opening area as a function of the signal pressure.
Tabulated data - Volumetric flow rate vs. pressure - the reference curve of the flow rate and differential pressure of the pressure reducing valve is used.
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
#Set pressure (gauge) —
overpressure above which the valve is triggered
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Details
The overpressure above which the valve will actuate. When the pressure in port B reaches this value, the valve begins to close. This parameter shifts the reference curve so that the pressure reducing valve begins to close when the pressure at port B is equal to the set 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 —
pressure control range
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Details
The operating pressure range of the valve. The pressure control range determines the difference between the parameters Set pressure (gauge) and the maximum operating pressure of the valve.
Dependencies
To use this parameter, set the parameter Opening parameterization to . Linear - Area vs. pressure.
Units
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Default value
0.01 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
Cross-sectional area of the valve bore in the fully open position.
Dependencies
To use this parameter, set the parameters Opening parameterization to . Linear - Area vs. pressure.
#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.
A continuous smoothing factor that specifies the degree of change in flow response when the valve is 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 Linear - Area vs. pressure.
Default value
0.01
Program usage name
smoothing_factor
Evaluatable
Yes
#Pressure recovery —
whether to take into account the pressure increase when the area expands
Details
Whether to take into account the pressure increase when the fluid flows from a region with a smaller cross-sectional area to a region with a larger cross-sectional area.
Dependencies
To use this parameter, set the parameters Opening parameterization 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 —
whether to take into account the flow response to valve opening
Details
Whether to account for transient effects in the fluid system caused by valve opening. Checking Opening dynamics approximates the opening conditions by introducing a first order lag in the flow response. The simulated opening dynamics are controlled by the Opening time constant parameters.
Default value
false (switched off)
Program usage name
opening_dynamics
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 at port B (gauge) vector —
vector of overpressure values for the tabular parameterization of the area
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Details
Overpressure vector for the tabular parameterization of the valve opening area. The elements of the vector must correspond to the elements of the Opening area vector parameters. The elements must be positive and in ascending order. The block uses linear interpolation between data points.
Dependencies
To use this parameter, set the Opening parameterization parameter to Tabulated data - Area 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 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
Valve opening area vector for tabular parameterization of the valve opening area. The elements of the vector must correspond to the elements of the parameter Pressure at Port B (gauge) vector. The elements must be positive and in ascending order. The block uses linear interpolation between data points.
Dependencies
To use this parameter, set the Opening parameterization parameter to Tabulated data - Area vs. pressure.
#Reference pressure at port A (gauge) —
port reference pressure A Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Details
Constant pressure at port A on which the reference curve is based. This value usually corresponds to the maximum operating pressure of the valve. During simulation, the pressure at port A can be any pressure.
Dependencies
To use this parameter, 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
1.5 MPa
Program usage name
p_inlet_gauge_reference
Evaluatable
Yes
#Reference pressure at port B (gauge) vector —
port reference pressure B Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Details
Vector of monotonically decreasing values of pressure at port B on the reference curve as the valve opening area changes. The first element is the reference maximum pressure at which the valve closes completely. The last element is the reference control pressure.
Dependencies
To use this parameter, set the parameters Opening parameterization to . Tabulated data - Volumetric flow rate vs. pressure.
Units
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Vector of monotonically increasing reference flow values through the valve. The block uses this curve to calculate the flow coefficient for a varying valve area.
Dependencies
To use this parameter, set the parameters Opening parameterization to Tabulated data - Volumetric flow rate vs. pressure.