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# 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

where:

• $\stackrel{˙}{m}$ is the mass flow rate from port A to port B.

• ρA and ρB are densities at ports A and B, respectively.

• $\stackrel{˙}{V}$ is the volumetric flow rate.

The equations describing the source use these symbols.

 cp Specific heat at constant pressure h Specific enthalpy ht Specific total enthalpy $\stackrel{˙}{m}$ 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 Φwork Power delivered to the moist air flow through the source

Subscripts A and B indicate the appropriate port.

Mass balance:

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

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

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

where

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

The mixture-specific enthalpies, hA = h(TA) and hB = h(TB), 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

`${\stackrel{˙}{m}}_{A}={\stackrel{˙}{m}}_{specified}$`

### 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 mass flow rate of the moist air through the source.

#### Dependencies

To enable this port, set the Source type parameter to `Controlled` and Flow rate type to `Mass flow rate`.

Input physical signal that specifies the volumetric flow rate of moist air through the source.

#### Dependencies

To enable this port, set the Source type parameter to `Controlled` and Flow rate type to `Volumetric flow rate`.

### Conserving

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Moist air conserving port. A positive flow rate causes moist air to flow from port A to port B.

Moist air conserving port. A positive flow rate causes moist air to flow from port A to port B.

## Parameters

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Select whether the flow rate generated by the source can change during simulation:

• `Controlled` — The flow rate is variable, controlled by an input physical signal. Selecting this option exposes the input port M or V, depending on the value of the Flow rate type parameter.

• `Constant` — The flow rate is constant during simulation, specified by a block parameter. Selecting this option enables the Mass flow rate or Volumetric flow rate parameter, depending on the value of the Flow rate type parameter.

Select the type of flow rate, `Mass flow rate` or `Volumetric flow rate`.

Desired mass flow rate of the moist air mixture through the source.

#### Dependencies

To enable this parameter, set Source type to `Constant` and Flow rate type to `Mass flow rate`.

Desired volumetric flow rate of the moist air mixture through the source.

#### Dependencies

To enable this parameter, set Source type to `Constant` and Flow rate type to `Volumetric flow rate`.

Select whether the source calculates flow rate at actual working conditions or at a standard pressure and temperature:

• `Actual conditions` — The source calculates the volumetric flow rate by using the moist air density at the actual working conditions of the system.

• `Standard conditions` — The source calculates the volumetric flow rate by using the moist air density at standard conditions. When you select this option, additional parameters become available to let you specify the standard pressure, temperature, and relative humidity.

#### Dependencies

To enable this parameter, set Flow rate type to `Volumetric flow rate`.

Moist air pressure at standard conditions.

#### Dependencies

To enable this parameter, set Specified flow rate conditions to `Standard conditions`.

Moist air temperature at standard conditions.

#### Dependencies

To enable this parameter, set Specified flow rate conditions to `Standard conditions`.

Select whether the source performs work on the moist air flow:

• `Isentropic` — The source performs isentropic work on the moist air to maintain the specified mass flow rate. 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 mass flow rate 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 R2023b

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