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.

cp	Specific heat at constant pressure
h	Specific enthalpy
ht	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
Φwork	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:

$$\begin{array}{l}{\dot{m}}_A+{\dot{m}}_B=0\\ {\dot{m}}_{wA}+{\dot{m}}_{wB}=0\\ {\dot{m}}_{gA}+{\dot{m}}_{gB}=0\\ {\dot{m}}_{dA}+{\dot{m}}_{dB}=0\end{array}$$

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:

$${\displaystyle {\int }_{T_A}^{T_B}\frac{1}{T}}dh\left(T\right)=R\ln \left(\frac{p_B}{p_A}\right)$$

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

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.

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.

Conserving

A — Source inlet

moist air

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

B — Source outlet

moist air

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

Parameters

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.

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.

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.

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.

Specified flow rate conditions — Select whether to calculate volumetric flow rate at standard or actual working conditions

Actual conditions (default) | Standard conditions

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.

Standard pressure — Moist air pressure at standard conditions

0.10132 MPa (default)

Moist air pressure at standard conditions.

Dependencies

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

Standard temperature — Moist air temperature at standard conditions

20 degC (default)

Moist air temperature at standard conditions.

Dependencies

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

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 temperature of the flow.

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.

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.

Extended Capabilities

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

Version History

Introduced in R2023b

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);