# Controlled Reservoir (MA)

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

Libraries:
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, φw

• Specific humidity, xw

• Water vapor mole fraction, yw

• Humidity ratio, rw

• Wet-bulb temperature, Tw

You can specify trace gas as one of:

• Trace gas mass fraction, xg

• Trace gas mole fraction, yg

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.

The block calculates the wet-bulb temperature implicitly by using this equation:

`${x}_{w}=\frac{\left(1-{x}_{g}\left(T\right)\right)\left({h}_{a}\left({T}_{w}\right)-{h}_{a}\left(T\right)\right)+{x}_{g}\left({h}_{g}\left({T}_{w}\right)-{h}_{g}\left(T\right)\right)+\frac{{x}_{ws}\left({T}_{w}\right)}{1-{x}_{ws}\left({T}_{w}\right)}\Delta {h}_{fg}\left({T}_{w}\right)}{\left({h}_{a}\left({T}_{w}\right)-{h}_{a}\left(T\right)\right)\left({h}_{w}\left({T}_{w}\right)-{h}_{w}\left(T\right)\right)+\frac{1}{1-{x}_{ws}\left({T}_{w}\right)}\Delta {h}_{fg}\left({T}_{w}\right)}$`

where:

• T is the temperature.

• Tw is the wet-bulb temperature.

• xw(T) is the specific humidity.

• xg(T) is the trace gas mass fraction.

• xws(Tw) is the specific humidity of saturation at the wet bulb temperature.

• ha(T) is the specific enthalpy of the dry air.

• ha(Tw) is the specific enthalpy of the dry air at the wet bulb temperature.

• hg(T) is the specific enthalpy of the trace gas.

• hg(Tw) is the specific enthalpy of the trace gas at the wet bulb temperature.

• hw(T) is the specific enthalpy of the water vapor.

• hw(Tw) is the specific enthalpy of the water vapor at the wet bulb temperature.

• Δhfg(Tw) is the specific enthalpy of vaporization of water vapor at the wet-bulb temperature.

## Ports

### Input

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Physical signal port that provides the reservoir pressure control signal.

Physical signal port that provides the reservoir temperature control 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.

#### Dependencies

To enable this port, set the Reservoir moisture specification parameter to

• `Relative humidity`

• `Specific humidity`

• `Mole fraction`

• `Humidity ratio`

Physical signal port that controls the reservoir wet-bulb temperature.

#### Dependencies

To enable this port, set the Reservoir moisture specification parameter to ```Wet-bulb temperature```.

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

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Moist air conserving port associated with the reservoir inlet.

## Parameters

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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.

• `Wet-bulb temperature` ― Physical signal port W specifies the wet-bulb temperature.

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

The cross-sectional area of the reservoir inlet.

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.

## Version History

Introduced in R2018a

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