Pressure Source (G)

Generate constant or time-varying pressure differential

Libraries:
Simscape / Foundation Library / Gas / Sources

Description

The Pressure Source (G) block represents an ideal mechanical energy source in a gas network. The source can maintain a constant pressure differential across its ports regardless of the flow rate through the source. There is no flow resistance and no heat exchange with the environment.

Ports A and B represent the source inlet and outlet. The input physical signal at port P specifies the pressure differential. Alternatively, you can specify a constant pressure differential as a block parameter. A positive pressure differential causes the pressure at port B to be greater than the pressure at port A.

You can choose whether the source performs work on the gas flow:

If the source is isentropic (Power added parameter is set to Isentropic), then the isentropic relation depends on the gas property model.
Gas Model Equations
Perfect gas $\frac{{(p_{A})}^{Z \cdot R / c_{p}}}{T_{A}} = \frac{{(p_{B})}^{Z \cdot R / c_{p}}}{T_{B}}$
Semiperfect gas $\int_{0}^{T_{A}} \frac{c_{p} (T)}{T} d T - Z \cdot R \cdot \ln (p_{A}) = \int_{0}^{T_{B}} \frac{c_{p} (T)}{T} d T - Z \cdot R \cdot \ln (p_{B})$
Real gas $s (T_{A}, p_{A}) = s (T_{B}, p_{B})$
The power delivered to the gas flow is based on the specific total enthalpy associated with the isentropic process.
$Φ_{w o r k} = - {\dot{m}}_{A} (h_{A} + \frac{w_{A}^{2}}{2}) - {\dot{m}}_{B} (h_{B} + \frac{w_{B}^{2}}{2})$
If the source performs no work (Power added parameter is set to None), then the defining equation states that the specific total enthalpy is equal on both sides of the source. It is the same for all three gas property models.
$h_{A} + \frac{w_{A}^{2}}{2} = h_{B} + \frac{w_{B}^{2}}{2}$
The power delivered to the gas flow Φ_work = 0.

Gas Model	Equations
Perfect gas	$\frac{{(p_{A})}^{Z \cdot R / c_{p}}}{T_{A}} = \frac{{(p_{B})}^{Z \cdot R / c_{p}}}{T_{B}}$
Semiperfect gas	$\int_{0}^{T_{A}} \frac{c_{p} (T)}{T} d T - Z \cdot R \cdot \ln (p_{A}) = \int_{0}^{T_{B}} \frac{c_{p} (T)}{T} d T - Z \cdot R \cdot \ln (p_{B})$
Real gas	$s (T_{A}, p_{A}) = s (T_{B}, p_{B})$

The equations use these symbols:

c_p	Specific heat at constant pressure
h	Specific enthalpy
$\dot{m}$	Mass flow rate (flow rate associated with a port is positive when it flows into the block)
p	Pressure
R	Specific gas constant
s	Specific entropy
T	Temperature
w	Flow velocity
Z	Compressibility factor
Φ_work	Power delivered to the gas flow through the source

Subscripts A and B indicate the appropriate port.

Assumptions and Limitations

There are no irreversible losses.
There is no heat exchange with the environment.

Examples

Pneumatic Actuation Circuit

How the Foundation Library gas components can be used to model a controlled pneumatic actuator. The Directional Valve is a masked subsystem created from Variable Local Restriction (G) blocks to model the opening and closing of the flow paths. The Double-Acting Actuator is a masked subsystem created from Translational Mechanical Converter (G) blocks to model the interface between the gas network and the mechanical translational network.

Open Model

Pneumatic Motor Circuit

How a pneumatic vane motor can be modeled using the Simscape™ language. The Pneumatic Motor component is built using the Simscape Foundation gas domain. It inherits from the foundation.gas.two_port_steady base class, which contains common equations that implement the upwind energy flow rate and the gas properties at the ports. The Pneumatic Motor subclass implements equations that describe behaviors specific to the component, such as the motor torque and flow rate characteristics and the mass and energy balance. The Pneumatic Motor block is inserted into the model using the Simscape Component block without the need to generate a separate library.

Open Model

Ports

Input

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P — Pressure differential control signal, Pa
physical signal

Input physical signal that specifies the pressure differential across the source.

Dependencies

To enable this port, set the Source type parameter to Controlled.

Conserving

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A — Source inlet
gas

Gas conserving port. A positive pressure differential causes the pressure at port B to be greater than the pressure at port A.

B — Source outlet
gas

Gas conserving port. A positive pressure differential causes the pressure at port B to be greater than the pressure at port A.

Parameters

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Source type — Select whether pressure differential can change during simulation
`Controlled` (default) | `Constant`

Select whether the pressure differential generated by the source can change during simulation:

Controlled — The pressure differential is variable, controlled by an input physical signal. Selecting this option exposes the input port P.
Constant — The pressure differential is constant during simulation, specified by a block parameter. Selecting this option enables the Pressure differential parameter.

Pressure differential — Constant pressure differential across the source
0 MPa (default) | scalar

Gas pressure differential across the ports of the source.

Dependencies

To enable this parameter, set Source type to Constant.

Power added — Select whether the source performs work
`Isentropic` (default) | `None`

Select whether the source performs work on the gas flow:

Isentropic — The source performs isentropic work on the gas to maintain the specified pressure differential. Use this option to represent an idealized pump or compressor and properly account for the energy input and output, especially in closed-loop systems.
None — The source performs no work on the flow, neither adding nor removing power, regardless of the pressure differential produced by the source. Use this option to set up the desired flow condition upstream of the system, without affecting the temperature of the flow.

Cross-sectional area at port A — Area normal to flow path at port A
0.01 m^2 (default) | positive scalar

Area normal to flow path at port A.

Cross-sectional area at port B — Area normal to flow path at port B
0.01 m^2 (default) | positive scalar

Area normal to flow path at port B.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2016b

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R2023b: Usability enhancement for gas sources

In R2023b, separate Pressure Source (G) and Controlled Pressure Source (G) blocks have been combined into a single Pressure Source (G) block that lets you select between generating constant or time-varying pressure differential.

This change has no compatibility impact when you use these Foundation library blocks in your models. When you open an existing model, the Controlled Pressure Source (G) blocks are automatically replaced by Pressure Source (G) blocks with exposed input port.

However, if you use these blocks in your custom composite components, you need to update the composite component code.

Source Block to Update	Old Syntax	New Syntax
Controlled Pressure Source (G)	`source = foundation.gas.sources.controlled_pressure_source;`	`source = foundation.gas.sources.pressure_source;`
Pressure Source (G)	`source = foundation.gas.sources.pressure_source;`	`source = foundation.gas.sources.pressure_source(source_type=foundation.enum.constant_controlled.constant);`

Pressure Source (G)