Moisture Source (MA)

Inject or extract moisture at a constant 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 source or sink of moisture for the connected moist air volume. A positive or negative moisture mass flow rate results in moisture being added or removed, respectively.

You can add moisture as water vapor or liquid water. For water vapor, the energy associated with the added or removed moisture 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 Moisture mass flow rate parameter.

• h_w is the water vapor specific enthalpy.

• T_specified is the temperature of added moisture, as specified 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.

For liquid water, the energy associated with the added or removed moisture 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

Conserving

S — Inject or extract moisture

moist air source

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

Parameters

Moisture added or removed — Select whether the source adds or removes moisture as water vapor or liquid water

Vapor (default) | Liquid

Select whether the source adds or removes moisture as water vapor or liquid water:

• Vapor — The enthalpy of the added or removed moisture corresponds to the enthalpy of water vapor, which is greater than that of liquid water.

• Liquid — The enthalpy of the added or removed moisture corresponds to the enthalpy of liquid water, which is less than that of water vapor.

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

0 kg/s (default)

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

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.

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

Enabled when the Added moisture temperature specification parameter is set to Specified temperature.

Extended Capabilities

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

Version History

Introduced in R2018a