Controlled Reservoir (MA)

Boundary conditions for moist air network at time-varying pressure, temperature, moisture, and trace gas levels

• Library:

• Simscape / Foundation Library / Moist Air / Elements

• 

Description

The Controlled Reservoir (MA) block sets controlled 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 control physical signals at ports P, T, W, and G, respectively. The inputs are limited by their valid ranges. For pressure and temperature, the valid range is between the minimum and maximum values specified in the Moist Air Properties (MA) block connected to the circuit. For the amount of moisture, the valid range is between zero and either saturation or 100 percent water vapor. For the amount of trace gas, the valid range is between zero and either the fraction left over after water vapor or 100 percent trace gas. The input G is 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

Input

P — Pressure control signal, Pa

physical signal

Physical signal port that provides the reservoir pressure control signal.

T — Temperature control signal, K

physical signal

Physical signal port that provides the reservoir temperature control signal.

W — Moisture control signal, unitless

physical signal

Physical signal port that controls the reservoir moisture level. To select the quantity that the control signal represents, use the Reservoir moisture specification parameter.

G — Trace gas control signal, unitless

physical signal

Physical signal port that controls the reservoir trace gas level. To select the quantity that the control signal represents, use the Reservoir trace gas specification parameter.

Conserving

A — Reservoir inlet

moist air

Moist air conserving port associated with the reservoir inlet.

Parameters

Reservoir moisture specification — Select the moisture property that the control signal represents

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

Select a moisture property:

• Relative humidity ― Physical signal at port W specifies the relative humidity.

• Specific humidity ― Physical signal at port W specifies the specific humidity.

• Mole fraction ― Physical signal at port W specifies the water vapor mole fraction.

• Humidity ratio ― Physical signal at port W specifies the humidity ratio.

Reservoir trace gas specification — Select the trace gas property that the control signal represents

Mass fraction (default) | Mole fraction

Select a trace gas property:

• Mass fraction ― Physical signal at port G specifies the trace gas mass fraction.

• Mole fraction ― Physical signal at port G specifies the trace gas 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.

Inputs outside valid range — Select what happens when the input signal values are outside of valid range

Warn and limit to valid values (default) | Limit to valid values | Error

Select what happens when the input signal values are outside of valid range:

• Limit to valid values ― The block uses the minimum or maximum valid values, but does not issue a warning.

• Warn and limit to valid values ― The block issues a warning and uses the corresponding minimum or maximum valid values.

• Error ― Simulation stops with an error.

Model Examples

Aircraft Environmental Control System

Models an aircraft environmental control system (ECS) that regulates pressure, temperature, humidity, and ozone (O3) to maintain a comfortable and safe cabin environment. Cooling and dehumidification are provided by the air cycle machine (ACM), which operates as an inverse Brayton cycle to remove heat from pressurized hot engine bleed air. Some hot bleed air is mixed directly with the output of the ACM to adjust the temperature. Pressurization is maintained by the outflow valve in the cabin. This model simulates the ECS operating from a hot ground condition to a cold cruise condition and back to a cold ground condition.

Open Model

Extended Capabilities

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

Version History

Introduced in R2018a