Reservoir (MA)

Boundary conditions for moist air network at constant pressure, temperature, moisture, and trace gas levels

• Library:

• Simscape / Foundation Library / Moist Air / Elements

• 

Description

The Reservoir (MA) block sets boundary conditions in a moist air network. The volume of moist air inside the reservoir is assumed infinite. Therefore, the flow is assumed quasi-steady. Moist air leaves the reservoir at the reservoir pressure, temperature, specific humidity, and trace gas mass fraction. Moist air enters the reservoir at the reservoir pressure, but the temperature, specific humidity, and trace gas mass fraction are determined by the moist air network upstream.

You specify the reservoir pressure, temperature, amount of moisture, and amount of trace gas by entering block parameter values. Block parameters related to trace gas are ignored if Trace gas model in the Moist Air Properties (MA) block is set to None.

You can specify moisture as one of:

• Relative humidity, φ_w

• Specific humidity, x_w

• Water vapor mole fraction, y_w

• Humidity ratio, r_w

You can specify trace gas as one of:

• Trace gas mass fraction, x_g

• Trace gas mole fraction, y_g

These moisture and trace gas quantities are related to each other as follows:

$$\begin{array}{l}{\phi }_w=\frac{y_{w}p}{p_{ws}}\\ y_w=\frac{x_w{R}_w}{R}\\ r_w=\frac{x_w}{1-x_w}\\ y_g=\frac{x_g{R}_g}{R}\\ x_a+x_w+x_g=1\\ R=x_a{R}_a+x_w{R}_w+x_g{R}_g\end{array}$$

where:

• p is pressure.

• R is specific gas constant.

Subscripts a, w, and g indicate the properties of dry air, water vapor, and trace gas, respectively. Subscript ws indicates water vapor at saturation.

Ports

Conserving

A — Reservoir inlet

moist air

Moist air conserving port associated with the reservoir inlet.

Parameters

Reservoir pressure specification — Select specification method for reservoir pressure

Atmospheric pressure (default) | Specified pressure

Select a specification method for the reservoir pressure:

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

• Specified pressure — Specify a value by using the Reservoir pressure parameter.

Reservoir pressure — Pressure in the reservoir

0.101325 MPa (default)

Enter the desired pressure in the reservoir. This pressure remains constant during simulation.

Dependencies

Enabled when the Reservoir pressure specification parameter is set to Specified pressure.

Reservoir temperature specification — Select specification method for reservoir temperature

Atmospheric temperature (default) | Specified temperature

Select a specification method for the reservoir 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 Reservoir temperature parameter.

Reservoir temperature — Temperature in the reservoir

293.15 K (default)

Enter the desired temperature in the reservoir. This temperature remains constant during simulation.

Dependencies

Enabled when the Reservoir temperature specification parameter is set to Specified temperature.

Reservoir moisture specification — Select the moisture property

Relative humidity (default) | Specific humidity | Mole fraction | Humidity ratio

Select a moisture property:

• Relative humidity ― Specify moisture using the relative humidity.

• Specific humidity ― Specify moisture using the specific humidity.

• Mole fraction ― Specify moisture using the water vapor mole fraction.

• Humidity ratio ― Specify moisture using the humidity ratio.

Reservoir relative humidity — Relative humidity in the reservoir

0.5 (default)

Enter the desired relative humidity in the reservoir. This value remains constant during simulation.

Dependencies

Enabled when the Reservoir moisture specification parameter is set to Relative humidity.

Reservoir specific humidity — Specific humidity in the reservoir

0.01 (default)

Enter the desired specific humidity in the reservoir. This value remains constant during simulation.

Dependencies

Enabled when the Reservoir moisture specification parameter is set to Specific humidity.

Reservoir water vapor mole fraction — Water vapor mole fraction in the reservoir

0.01 (default)

Enter the desired water vapor mole fraction in the reservoir. This value remains constant during simulation.

Dependencies

Enabled when the Reservoir moisture specification parameter is set to Mole fraction.

Reservoir humidity ratio — Humidity ratio in the reservoir

0.01 (default)

Enter the desired relative humidity in the reservoir. This value remains constant during simulation.

Dependencies

Enabled when the Reservoir moisture specification parameter is set to Humidity ratio.

Reservoir trace gas specification — Select the trace gas property

Mass fraction (default) | Mole fraction

Select a trace gas property:

• Mass fraction ― Specify the trace gas mass fraction.

• Mole fraction ― Specify the trace gas mole fraction.

Reservoir trace gas mass fraction — Trace gas mass fraction in the reservoir

0.001 (default)

Enter the desired trace gas mass fraction in the reservoir. This value remains constant during simulation.

Dependencies

Enabled when the Reservoir trace gas specification parameter is set to Mass fraction.

Reservoir trace gas mole fraction — Trace gas mole fraction in the reservoir

0.001 (default)

Enter the desired trace gas mole fraction in the reservoir. This value remains constant during simulation.

Dependencies

Enabled when the Reservoir trace gas specification parameter is set to Mole fraction.

Relative humidity at saturation — Relative humidity above which condensation occurs

1 (default)

Relative humidity above which condensation occurs. Amount of moisture in the reservoir must be less than saturation.

Cross-sectional area at port A — Area normal to flow path at the reservoir inlet

0.01 m^2 (default)

The cross-sectional area of the reservoir inlet.

Model 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

Pneumatic Actuator with Humidity

How the Simscape™ Foundation Library moist air components can be used to model a pneumatic actuator operating in a humid environment. The Directional Valve is a subsystem composed of four Variable Local Restriction (MA) blocks, and the Double-Acting Actuator is a subsystem composed of two Translational Mechanical Converter (MA) blocks in opposite mechanical orientation.

Open Model

Extended Capabilities

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

Version History

Introduced in R2018a