Main Content

Generate constant volumetric flow rate

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

The Volumetric Flow Rate Source (G) block represents an
ideal mechanical energy source in a gas network. The source can maintain a constant
volumetric flow rate regardless of the pressure differential. There is no flow
resistance and no heat exchange with the environment. A positive volumetric flow rate
causes gas to flow from port **A** to port
**B**.

The volumetric flow rate and mass flow rate are related through the expression

$$\dot{m}=\{\begin{array}{ll}{\rho}_{B}\dot{V}\hfill & \text{for}\dot{V}\ge 0\hfill \\ {\rho}_{A}\dot{V}\hfill & \text{for}\dot{V}0\hfill \end{array}$$

where:

*$$\dot{m}$$*is the mass flow rate from port**A**to port**B**.*ρ*_{A}and*ρ*_{B}are densities at ports**A**and**B**, respectively.*$$\dot{V}$$*is the volumetric flow rate.

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.

There are no irreversible losses.

There is no heat exchange with the environment.