# Flow Rate Source (G)

Generate constant or time-varying mass flow rate or volumetric flow rate in gas network

*Since R2023b*

**Libraries:**

Simscape /
Foundation Library /
Gas /
Sources

## Description

The Flow Rate Source (G) block represents an ideal
mechanical energy source in a gas network. The source can maintain the specified mass flow
rate or volumetric flow rate regardless of the pressure differential. There is no flow
resistance and no heat exchange with the environment. You specify the flow rate type by using
the **Flow rate type** parameter.

The block icon changes depending on the values of the **Source type** and
**Flow rate type** parameters.

Ports **A** and **B** represent the source inlet and
outlet. The input physical signal at port **M** or **V**,
depending on the flow rate type, specifies the flow rate. Alternatively, you can specify a
fixed flow rate as a block parameter. A positive 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`

), 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.

### Assumptions and Limitations

There are no irreversible losses.

There is no heat exchange with the environment.

## Ports

### Input

### Conserving

## Parameters

## Extended Capabilities

## Version History

**Introduced in R2023b**