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 ModelEquations
Perfect gas$\frac{{\left({p}_{A}\right)}^{Z\cdot R/{c}_{p}}}{{T}_{A}}=\frac{{\left({p}_{B}\right)}^{Z\cdot R/{c}_{p}}}{{T}_{B}}$
Semiperfect gas${\int }_{0}^{{T}_{A}}\frac{{c}_{p}\left(T\right)}{T}dT-Z\cdot R\cdot \mathrm{ln}\left({p}_{A}\right)={\int }_{0}^{{T}_{B}}\frac{{c}_{p}\left(T\right)}{T}dT-Z\cdot R\cdot \mathrm{ln}\left({p}_{B}\right)$
Real gas$s\left({T}_{A},{p}_{A}\right)=s\left({T}_{B},{p}_{B}\right)$

The power delivered to the gas flow is based on the specific total enthalpy associated with the isentropic process.

`${\Phi }_{work}=-{\stackrel{˙}{m}}_{A}\left({h}_{A}+\frac{{w}_{A}^{2}}{2}\right)-{\stackrel{˙}{m}}_{B}\left({h}_{B}+\frac{{w}_{B}^{2}}{2}\right)$`
• 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 Φwork = 0.

The equations use these symbols:

 cp Specific heat at constant pressure h Specific enthalpy $\stackrel{˙}{m}$ 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 Φwork 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.

Ports

Input

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

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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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.

Gas pressure differential across the ports of the source.

Dependencies

To enable this parameter, set Source type to `Constant`.

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.

Area normal to flow path at port A.

Area normal to flow path at port B.

Version History

Introduced in R2016b

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