# Flow Rate Source (MA)

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

*Since R2023b*

**Libraries:**

Simscape /
Foundation Library /
Moist Air /
Sources

## Description

The Flow Rate Source (MA) block represents an ideal
mechanical energy source in a moist air 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.

The equations describing the source use these symbols.

c_{p} | Specific heat at constant pressure |

h | Specific enthalpy |

h_{t} | Specific total enthalpy |

$$\dot{m}$$ | Mass flow rate (flow rate associated with a port is positive when it flows into the block) |

p | Pressure |

ρ | Density |

R | Specific gas constant |

s | Specific entropy |

T | Temperature |

Φ_{work} | Power delivered to the moist air flow through the source |

Subscripts A and B indicate the appropriate port.

Mass balance:

$$\begin{array}{l}{\dot{m}}_{A}+{\dot{m}}_{B}=0\\ {\dot{m}}_{wA}+{\dot{m}}_{wB}=0\\ {\dot{m}}_{gA}+{\dot{m}}_{gB}=0\end{array}$$

Energy balance:

$${\Phi}_{A}+{\Phi}_{B}+{\Phi}_{work}=0$$

If the source performs no work (**Power added** parameter is set to
`None`

), then $${\Phi}_{work}=0$$.

If the source is isentropic (**Power added** parameter is set to
`Isentropic`

), then

$${\Phi}_{work}={\dot{m}}_{A}\left({h}_{tB}-{h}_{tA}\right)$$

where

$$\begin{array}{l}{h}_{tA}={h}_{A}+\frac{1}{2}{\left(\frac{{\dot{m}}_{A}}{{\rho}_{A}{S}_{A}}\right)}^{2}\\ {h}_{tB}={h}_{B}+\frac{1}{2}{\left(\frac{{\dot{m}}_{B}}{{\rho}_{B}{S}_{B}}\right)}^{2}\end{array}$$

The mixture-specific enthalpies, *h*_{A} =
*h*(*T*_{A}) and
*h*_{B} =
*h*(*T*_{B}), are constrained by
the isentropic relation, that is, there is no change in entropy:

$${\int}_{{T}_{A}}^{{T}_{B}}\frac{1}{T}}dh\left(T\right)=R\mathrm{ln}\left(\frac{{p}_{B}}{{p}_{A}}\right)$$

When you set the **Flow rate type** parameter to ```
Mass flow
rate
```

, the quantity specified by the **Mixture mass flow
rate** parameter or the input signal at port **M** is

$${\dot{m}}_{A}={\dot{m}}_{specified}$$

### 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**