Flow Rate Source (MA)

R2026b

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

$\dot{m} = {\begin{array}{l} ρ_{B} \dot{V} & for \dot{V} \geq 0 \\ ρ_{A} \dot{V} & for \dot{V} < 0 \end{array}$

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. Subscripts a, w, d, and g indicate the properties of dry air, water vapor, water droplets, and trace gas, respectively.

Mass balance:

$\begin{array}{l} {\dot{m}}_{A} + {\dot{m}}_{B} = 0 \\ {\dot{m}}_{w A} + {\dot{m}}_{w B} = 0 \\ {\dot{m}}_{g A} + {\dot{m}}_{g B} = 0 \\ {\dot{m}}_{d A} + {\dot{m}}_{d B} = 0 \end{array}$

Energy balance:

$Φ_{A} + Φ_{B} + Φ_{w o r k} = 0$

If the source performs no work (Power added parameter is set to None), then $Φ_{w o r k} = 0$ .

If the source is isentropic (Power added parameter is set to Isentropic), then

$Φ_{w o r k} = {\dot{m}}_{A} (h_{t B} - h_{t A})$

where

$\begin{array}{l} h_{t A} = h_{A} + \frac{1}{2} {(\frac{{\dot{m}}_{A}}{ρ_{A} S_{A}})}^{2} \\ h_{t B} = h_{B} + \frac{1}{2} {(\frac{{\dot{m}}_{B}}{ρ_{B} S_{B}})}^{2} \end{array}$

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:

$\int_{T_{A}}^{T_{B}} \frac{1}{T} d h (T) = R \ln (\frac{p_{B}}{p_{A}})$

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

${\dot{m}}_{A} = {\dot{m}}_{s p e c i f i e d}$

Assumptions and Limitations

There are no irreversible losses.
There is no heat exchange with the environment.

Ports

Input

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M — Mass flow rate control signal, kg/s
physical signal

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.

Programmatic Use

Port: M

V — Volumetric flow rate control signal, m^3/s
physical signal

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.

Programmatic Use

Port: V

Conserving

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A — Source inlet
moist air

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

Programmatic Use

Port: A

B — Source outlet
moist air

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

Programmatic Use

Port: B

Parameters

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Source type — Select whether flow rate can change during simulation
`Controlled` (default) | `Constant`

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.

Programmatic Use

Parameter:	`source_type`
Values:	`"foundation.enum.constant_controlled.controlled"` \| `"foundation.enum.constant_controlled.constant"`

Flow rate type — Select whether source generates mass or volumetric flow rate
`Mass flow rate` (default) | `Volumetric flow rate`

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

Programmatic Use

Parameter:	`flow_type`
Values:	`"foundation.enum.mass_volumetric_flow.mass"` \| `"foundation.enum.mass_volumetric_flow.volumetric"`

Mixture mass flow rate — Constant mass flow rate through the source
`0 kg/s` (default)

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.

Programmatic Use

Parameter: mass_flow

Mixture volumetric flow rate — Constant volumetric flow rate through the source
`0 m^3/s` (default)

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.

Programmatic Use

Parameter: volumetric_flow

Specified flow rate conditions — Select whether to calculate volumetric flow rate at standard or actual working conditions
`Standard conditions` (default) | `Actual conditions`

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

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 let you specify the standard pressure, temperature, humidity, and trace gas amount.
Actual conditions — The source calculates the volumetric flow rate by using the moist air density at the actual working conditions of the system.

Dependencies

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

Programmatic Use

Parameter:	`volumetric_flow_conditions`
Values:	`"foundation.enum.volumetric_flow_conditions.standard"` \| `"foundation.enum.volumetric_flow_conditions.actual"`

Standard pressure — Moist air pressure at standard conditions
`0.101325 MPa` (default)

Moist air pressure at standard conditions.

Dependencies

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

Programmatic Use

Parameter: p_std

Standard temperature — Moist air temperature at standard conditions
`293.15 K` (default)

Moist air temperature at standard conditions.

Dependencies

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

Programmatic Use

Parameter: T_std

Standard humidity specification — Humidity specification
`Relative humidity` (default) | `Specific humidity` | `Mole fraction` | `Humidity ratio` | `Wet-bulb temperature`

Method to specify the initial moist air humidity.

Dependencies

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

Programmatic Use

Parameter:	`humidity_spec`
Values:	`"foundation.enum.HumiditySpec.RelativeHumidity"` \| `"foundation.enum.HumiditySpec.SpecificHumidity"` \| `"foundation.enum.HumiditySpec.MoleFraction"` \| `"foundation.enum.HumiditySpec.HumidityRatio"` \| `"foundation.enum.HumiditySpec.WetBulbTemperature"`

Standard relative humidity — Moist air relative humidity at standard conditions
`0.5` (default) | scalar in the range of [0,1]

Moist air relative humidity at standard conditions.

Dependencies

To enable this parameter, set Standard humidity specification to Relative humidity.

Programmatic Use

Parameter: RH_std

Standard specific humidity — Moist air specific humidity at standard conditions
`0.01` (default) | scalar in the range of [0,1]

Specific humidity in the moist air at standard conditions. The specific humidity is the mass fraction of water vapor to the combined total mass of water vapor, trace gas, and dry air.

Dependencies

To enable this parameter, set Standard humidity specification to Specific humidity.

Programmatic Use

Parameter: x_w_std

Standard water vapor mole fraction — Mole fraction of water vapor at standard conditions
`0.01` (default) | scalar in the range [0,1]

Mole fraction of the water vapor in the moist air channel at standard conditions. The water vapor mole fraction is relative to the combined molar quantity of water vapor, trace species, and dry air.

Dependencies

To enable this parameter, set Standard humidity specification to Mole fraction.

Programmatic Use

Parameter: y_w_std

Standard humidity ratio — Humidity ratio at standard conditions
`0.01` (default) | scalar in the range [0,1]

Humidity ratio in the moist air channel at standard conditions. The humidity ratio is the ratio of the mass of water vapor to the mass of dry air and trace gas.

Dependencies

To enable this parameter, set Standard humidity specification to Humidity ratio.

Programmatic Use

Parameter: HR_std

Standard wet-bulb temperature — Wet-bulb temperature at standard conditions
`287 K` (default)

Wet-bulb temperature at standard conditions. The block uses this value to calculate humidity.

Dependencies

To enable this parameter, set Standard humidity specification to Wet-bulb temperature.

Programmatic Use

Parameter: Tw_std

Standard trace gas specification — Measurement type of trace gas
`Mass fraction` (default) | `Mole fraction`

Measurement type of trace gas.

Dependencies

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

Programmatic Use

Parameter:	`trace_gas_spec`
Values:	`"foundation.enum.trace_gas_spec.mass_fraction"` \| `"foundation.enum.trace_gas_spec.mole_fraction"`

Standard trace gas mass fraction — Amount of trace gas in the moist air channel
`0` (default) | scalar in the range [0,1]

Amount of trace gas in the moist air by mass fraction at standard conditions. The mass fraction is relative to the combined total mass of water vapor, trace gas, and dry air.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set Standard trace gas specification to Mass fraction.

Programmatic Use

Parameter: x_g_std

Standard trace gas mole fraction — Amount of trace gas in the moist air channel
`0` (default) | scalar in the range [0,1]

Amount of trace gas in the moist air by mole fraction at standard conditions. The mole fraction is relative to the combined molar total of water vapor, trace gas, and dry air.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set Standard trace gas specification to Mole fraction.

Programmatic Use

Parameter: y_g_std

Relative humidity at saturation — Relative humidity above which condensation occurs
`1` (default)

Relative humidity above which condensation occurs.

Dependencies

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

Programmatic Use

Parameter: RH_ws

Power added — Select whether the source performs work
`Isentropic` (default) | `None`

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 enthalpy of the flow.

Programmatic Use

Parameter:	`power_spec`
Values:	`"foundation.enum.power_spec.isentropic"` \| `"foundation.enum.power_spec.none"`

Cross-sectional area at port A — Area normal to flow path at port A
`0.01 m^2` (default)

Area normal to flow path at port A.

Programmatic Use

Parameter: area_A

Cross-sectional area at port B — Area normal to flow path at port B
`0.01 m^2` (default)

Area normal to flow path at port B.

Programmatic Use

Parameter: area_B

Extended Capabilities

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C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2023b

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R2026b: Specify humidity and trace gas amounts at standard conditions

When calculating volumetric flow rate by using density at standard conditions, the block now provides a full range of humidity and trace gas parameterization options. Previously, the block allowed you to specify relative humidity only and assumed zero trace gas at standard conditions.

R2026a: Calculating volumetric flow rate by using density at standard conditions is now the default

When generating volumetric flow rate, the block lets you select whether to calculate the volumetric flow rate by using density at standard pressure and temperature or at the actual working conditions of the system. In previous releases, the default was to use actual working conditions. However, moist air density can vary significantly with pressure and temperature. Specifying mass flow rate directly or using volumetric rate at standard conditions makes the model more robust.

In general, when you are debugging a model that has initialization or robustness issues, try switching its Flow Rate Source (MA) blocks to use either mass flow rate or volumetric rate at standard conditions, resolve the issues, and then you can switch back to using actual working conditions, if desired.

R2024b: Model water droplets suspended in moist air flow

Blocks in the moist air domain can now model water droplets suspended in a moist air flow. To model water droplets, select Enable entrained water droplets in the Moist Air Properties (MA) block connected to your moist air network.

R2023b: Usability enhancement for moist air sources

In R2023b, separate Mass Flow Rate Source (MA), Controlled Mass Flow Rate Source (MA), Volumetric Flow Rate Source (MA), and Controlled Volumetric Flow Rate Source (MA) blocks have been combined into a single Flow Rate Source (MA) block that lets you select between generating constant or time-varying mass flow rate or volumetric flow rate. The new block lets you use the block parameters to configure the block and expose only the input ports that you need in a particular model, which helps reduce clutter and improve the block diagram layout.

This change has no compatibility impact when you use these Foundation library blocks in your models. When you open an existing model, the old blocks are automatically replaced by Flow Rate Source (MA) blocks with the appropriate configuration.

However, if you use these blocks in your custom composite components, you need to update the composite component code.

Source Block to Update	Old Syntax	New Syntax
Controlled Mass Flow Rate Source (MA)	`source = foundation.moist_air.sources.controlled_mass_flow_source;`	`source = foundation.moist_air.sources.flow_source;`
Mass Flow Rate Source (MA)	`source = foundation.moist_air.sources.mass_flow_source;`	`source = foundation.moist_air.sources.flow_source(source_type=foundation.enum.constant_controlled.constant);`
Controlled Volumetric Flow Rate Source (MA)	`source = foundation.moist_air.sources.controlled_volumetric_flow_source;`	`source = foundation.moist_air.sources.flow_source(flow_type=foundation.enum.mass_volumetric_flow.volumetric);`
Volumetric Flow Rate Source (MA)	`source = foundation.moist_air.sources.volumetric_flow_source;`	`source = foundation.moist_air.sources.flow_source(source_type=foundation.enum.constant_controlled.constant,flow_type=foundation.enum.mass_volumetric_flow.volumetric);`

Flow Rate Source (MA)

Description

Assumptions and Limitations

Ports

Input

M — Mass flow rate control signal, kg/s physical signal

Dependencies

Programmatic Use

V — Volumetric flow rate control signal, m^3/s physical signal

Dependencies

Programmatic Use

Conserving

A — Source inlet moist air

Programmatic Use

B — Source outlet moist air

Programmatic Use

Parameters

Source type — Select whether flow rate can change during simulation Controlled (default) | Constant

Programmatic Use

Flow rate type — Select whether source generates mass or volumetric flow rate Mass flow rate (default) | Volumetric flow rate

Programmatic Use

Mixture mass flow rate — Constant mass flow rate through the source 0 kg/s (default)

Dependencies

Programmatic Use

Mixture volumetric flow rate — Constant volumetric flow rate through the source 0 m^3/s (default)

Dependencies

Programmatic Use

Specified flow rate conditions — Select whether to calculate volumetric flow rate at standard or actual working conditions Standard conditions (default) | Actual conditions

Dependencies

Programmatic Use

Standard pressure — Moist air pressure at standard conditions 0.101325 MPa (default)

Dependencies

Programmatic Use

Standard temperature — Moist air temperature at standard conditions 293.15 K (default)

Dependencies

Programmatic Use

Standard humidity specification — Humidity specification Relative humidity (default) | Specific humidity | Mole fraction | Humidity ratio | Wet-bulb temperature

Dependencies

Programmatic Use

Standard relative humidity — Moist air relative humidity at standard conditions 0.5 (default) | scalar in the range of [0,1]

Dependencies

Programmatic Use

Standard specific humidity — Moist air specific humidity at standard conditions 0.01 (default) | scalar in the range of [0,1]

Dependencies

Programmatic Use

Standard water vapor mole fraction — Mole fraction of water vapor at standard conditions 0.01 (default) | scalar in the range [0,1]

Dependencies

Programmatic Use

Standard humidity ratio — Humidity ratio at standard conditions 0.01 (default) | scalar in the range [0,1]

Dependencies

Programmatic Use

Standard wet-bulb temperature — Wet-bulb temperature at standard conditions 287 K (default)

Dependencies

Programmatic Use

Standard trace gas specification — Measurement type of trace gas Mass fraction (default) | Mole fraction

Dependencies

Programmatic Use

Standard trace gas mass fraction — Amount of trace gas in the moist air channel 0 (default) | scalar in the range [0,1]

Dependencies

Programmatic Use

Standard trace gas mole fraction — Amount of trace gas in the moist air channel 0 (default) | scalar in the range [0,1]

Dependencies

Programmatic Use

Relative humidity at saturation — Relative humidity above which condensation occurs 1 (default)

Dependencies

Programmatic Use

Power added — Select whether the source performs work Isentropic (default) | None

Programmatic Use

Cross-sectional area at port A — Area normal to flow path at port A 0.01 m^2 (default)

Programmatic Use

Cross-sectional area at port B — Area normal to flow path at port B 0.01 m^2 (default)

Programmatic Use

Extended Capabilities

C/C++ Code Generation Generate C and C++ code using Simulink® Coder™.

Version History

R2026b: Specify humidity and trace gas amounts at standard conditions

R2026a: Calculating volumetric flow rate by using density at standard conditions is now the default

R2024b: Model water droplets suspended in moist air flow

R2023b: Usability enhancement for moist air sources

See Also

M — Mass flow rate control signal, kg/s
physical signal

V — Volumetric flow rate control signal, m^3/s
physical signal

A — Source inlet
moist air

B — Source outlet
moist air

Source type — Select whether flow rate can change during simulation
`Controlled` (default) | `Constant`

Flow rate type — Select whether source generates mass or volumetric flow rate
`Mass flow rate` (default) | `Volumetric flow rate`

Mixture mass flow rate — Constant mass flow rate through the source
`0 kg/s` (default)

Mixture volumetric flow rate — Constant volumetric flow rate through the source
`0 m^3/s` (default)

Specified flow rate conditions — Select whether to calculate volumetric flow rate at standard or actual working conditions
`Standard conditions` (default) | `Actual conditions`

Standard pressure — Moist air pressure at standard conditions
`0.101325 MPa` (default)

Standard temperature — Moist air temperature at standard conditions
`293.15 K` (default)

Standard humidity specification — Humidity specification
`Relative humidity` (default) | `Specific humidity` | `Mole fraction` | `Humidity ratio` | `Wet-bulb temperature`

Standard relative humidity — Moist air relative humidity at standard conditions
`0.5` (default) | scalar in the range of [0,1]

Standard specific humidity — Moist air specific humidity at standard conditions
`0.01` (default) | scalar in the range of [0,1]

Standard water vapor mole fraction — Mole fraction of water vapor at standard conditions
`0.01` (default) | scalar in the range [0,1]

Standard humidity ratio — Humidity ratio at standard conditions
`0.01` (default) | scalar in the range [0,1]

Standard wet-bulb temperature — Wet-bulb temperature at standard conditions
`287 K` (default)

Standard trace gas specification — Measurement type of trace gas
`Mass fraction` (default) | `Mole fraction`

Standard trace gas mass fraction — Amount of trace gas in the moist air channel
`0` (default) | scalar in the range [0,1]

Standard trace gas mole fraction — Amount of trace gas in the moist air channel
`0` (default) | scalar in the range [0,1]

Relative humidity at saturation — Relative humidity above which condensation occurs
`1` (default)

Power added — Select whether the source performs work
`Isentropic` (default) | `None`

Cross-sectional area at port A — Area normal to flow path at port A
`0.01 m^2` (default)

Cross-sectional area at port B — Area normal to flow path at port B
`0.01 m^2` (default)

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.