Moisture Source (MA)

Inject or extract moisture at a constant or time-varying rate

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Libraries:
Simscape / Foundation Library / Moist Air / Sources / Moisture & Trace Gas Sources

Description

The Moisture Source (MA) block represents a constant or time-varying source or sink of humidity or droplets for the connected moist air volume. A positive or negative moisture mass flow rate results in moisture being added or removed, respectively.

For a time-varying source, two physical signal input ports, M and T, supply the mass flow rate and temperature values, respectively. Alternatively, you can specify constant mass flow rate and temperature as block parameters.

When the Moisture added or removed parameter is Water vapor, the Water vapor evaporated from liquid or condensed to liquid parameter controls how the vapor leaves or enters the block. When you clear Water vapor evaporated from liquid or condensed to liquid, the block removes water vapor from the fluid volume at a specified rate. When you select Water vapor evaporated from liquid or condensed to liquid, the block assumes that the vapor that enters the fluid volume originates from evaporated water and that the vapor that leaves the volume condenses to liquid. In this case, the block also models the changes in latent heat from either process.

When you clear the Water vapor evaporated from liquid or condensed to liquid check box, the energy associated with the added or removed vapor is

$${\Phi }_s=\{\begin{array}{ll}{\dot{m}}_{specified}\cdot h_w\left(T_{specified}\right),\hfill & \text{if }{\dot{m}}_{specified}\ge 0\hfill \\ {\dot{m}}_{specified}\cdot h_w\left(T_s\right),\hfill & \text{if }{\dot{m}}_{specified}<0\hfill \end{array}$$

where:

• $${\dot{m}}_{specified}$$ is the water vapor mass flow rate specified by the input physical signal at port M or by the Rate of added moisture parameter.

• h_w is the water vapor specific enthalpy.

• T_specified is the temperature of added moisture, as specified by the input physical signal at port T or by the block parameters. The block uses this value to evaluate the specific enthalpy of the added moisture only. The specific enthalpy of removed moisture is based on the temperature of the connected moist air volume.

• T_s is the temperature at port S, which is the same as the temperature of the connected moist air volume.

When you select Water vapor evaporated from liquid or condensed to liquid, the energy associated with the added or removed vapor is

$${\Phi }_s=\{\begin{array}{ll}{\dot{m}}_{specified}\cdot \left(h_w\left(T_{specified}\right)-\Delta h_{vap}\left(T_{specified}\right)\right),\hfill & \text{if }{\dot{m}}_{specified}\ge 0\hfill \\ {\dot{m}}_{specified}\cdot \left(h_w\left(T_s\right)-\Delta h_{vap}\left(T_s\right)\right),\hfill & \text{if }{\dot{m}}_{specified}<0\hfill \end{array}$$

where Δh_vap is the water specific enthalpy of vaporization.

Port S is a moist air source conserving port. Connect this port to port S of a block with finite moist air volume to add or remove moisture through that block. For more information, see Using Moisture and Trace Gas Sources.

Examples

Medical Ventilator with Lung Model

Models a positive-pressure medical ventilator system. A preset flow rate is supplied to the patient. The lungs are modeled with the Translational Mechanical Converter (MA), which converts moist air pressure into translational motion. By setting the Interface cross-sectional area to unity, displacement in the mechanical translational network becomes a proxy for volume, force becomes a proxy for pressure, spring constant becomes a proxy for respiratory elastance, and damping coefficient becomes a proxy for respiratory resistance.

• Open Model

Ports

Input

M — Mass flow rate control signal, kg/s

physical signal

Input physical signal that specifies the water vapor or water droplets mass flow rate through the source.

Dependencies

To enable this port, set the Source type parameter to Controlled.

T — Temperature of added moisture, K

physical signal

Input physical signal that specifies the temperature of added moisture. The block uses this value to evaluate the specific enthalpy of the added moisture only. The specific enthalpy of removed moisture is based on the temperature of the connected moist air volume.

Dependencies

To enable this port, set the Source type parameter to Controlled.

Conserving

S — Inject or extract humidity or water droplets

moist air source

Connect this port to port S of a block with finite moist air volume to add or remove humidity or water droplets through that block.

Parameters

Source type — Select whether moisture mass flow rate and temperature can change during simulation

Controlled (default) | Constant

Select whether the moisture mass flow rate and temperature can change during simulation:

• Controlled — The moisture mass flow rate and temperature are variable, controlled by input physical signals. Selecting this option exposes the input ports M and T.

• Constant — The moisture mass flow rate and temperature are constant during simulation, specified by block parameters. Selecting this option enables these parameters.

Moisture added or removed — Select whether the block adds or removes moisture as water vapor or water droplets

Water vapor (default) | Water droplets

Select whether the block adds or removes moisture as water vapor or water droplets.

Water vapor evaporated from liquid or condensed to liquid — How the block adds or removes water vapor

off (default) | on

Select how the block adds or removes water vapor. If you clear this check box, the enthalpy of the added or removed moisture corresponds to the enthalpy of water vapor, which is greater than that of liquid water.

If you select this check box, the enthalpy of the added or removed moisture corresponds to the enthalpy of liquid water, which is less than that of water vapor. When water vapor is added, it evaporates from liquid and the latent heat is contributed by the connected fluid volume. When water vapor is removed, it condenses to liquid and the latent heat is released to the connected fluid volume.

Dependencies

To enable this parameter, set Moisture added or removed to Water vapor.

Rate of moisture added — Constant mass flow rate through the block

0 kg/s (default)

Water vapor or water droplets mass flow rate through the block. A positive value adds moisture to the connected moist air volume. A negative value extracts moisture from that volume.

Dependencies

To enable this parameter, set Source type to Constant.

Added moisture temperature specification — Select specification method for the temperature of added moisture

Atmospheric temperature (default) | Specified temperature

Select a specification method for the moisture temperature:

• Atmospheric temperature — Use the atmospheric temperature, specified by the Moist Air Properties (MA) block connected to the circuit.

• Specified temperature — Specify a value by using the Temperature of added moisture parameter.

Dependencies

To enable this parameter, set Source type to Constant.

Temperature of added moisture — Moisture temperature

293.15 K (default)

Enter the desired temperature of added moisture. This temperature remains constant during simulation. The block uses this value to evaluate the specific enthalpy of the added moisture only. The specific enthalpy of removed moisture is based on the temperature of the connected moist air volume.

Dependencies

To enable this parameter, set Source type to Constant and Added moisture temperature specification to Specified temperature.

Extended Capabilities

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

Version History

Introduced in R2018a

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 Moisture Source (MA) and Controlled Moisture Source (MA) blocks have been combined into a single Moisture Source (MA) block that lets you select between constant or time-varying source or sink of moisture.

This change has no compatibility impact when you use these Foundation library blocks in your models. When you open an existing model, the Controlled Moisture Source (MA) blocks are automatically replaced by Moisture Source (MA) blocks with exposed input ports.

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 Moisture Source (MA)	source = foundation.moist_air.sources.moisture_trace_gas.moisture_source_controlled;	source = foundation.moist_air.sources.moisture_trace_gas.moisture_source;
Moisture Source (MA)	source = foundation.moist_air.sources.moisture_trace_gas.moisture_source;	source = foundation.moist_air.sources.moisture_trace_gas.moisture_source(source_type=foundation.enum.constant_controlled.constant);