Generate time-varying mass flow rate

**Library:**Simscape / Foundation Library / Gas / Sources

The Mass Flow Rate Source (G) block represents an ideal mechanical energy source in a gas network. The mass flow rate is controlled by the input physical signal at port M. The source can maintain the specified mass flow rate regardless of the pressure differential. There is no flow resistance and no heat exchange with the environment. A positive mass flow rate causes gas to flow from port A to port B.

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

If the source is isentropic (

**Power added**parameter is set to`Isentropic power`

), then the isentropic relation depends on the gas property model.Gas Model Equations 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 $${\int}_{0}^{{T}_{A}}\frac{{c}_{p}\left(T\right)}{T}}dT-Z\cdot R\cdot \mathrm{ln}\left({p}_{A}\right)={\displaystyle {\int}_{0}^{{T}_{B}}\frac{{c}_{p}\left(T\right)}{T}}dT-Z\cdot R\cdot \mathrm{ln}\left({p}_{B}\right)$$ 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.

$${\Phi}_{work}=-{\dot{m}}_{A}\left({h}_{A}+\frac{{w}_{A}^{2}}{2}\right)-{\dot{m}}_{B}\left({h}_{B}+\frac{{w}_{B}^{2}}{2}\right)$$

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

*Φ*_{work}= 0.

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.

Use the **Variables** tab in the block dialog
box (or the **Variables** section in the block Property
Inspector) to set the priority and initial target values for the block
variables prior to simulation. For more information, see Set Priority and Initial Target for Block Variables and Initial Conditions for Blocks with Finite Gas Volume.

There are no irreversible losses, nor heat exchange with the environment.

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