# Reservoir (MA)

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

**Libraries:**

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}Wet-bulb temperature,

*T*_{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 the pressure.*R*is the 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.*T*_{w}is the wet-bulb temperature.*x*_{w}(*T*) is the specific humidity.*x*_{g}(*T*) is the trace gas mass fraction.*x*_{ws}(*T*_{w}) is the specific humidity of saturation at the wet bulb temperature.*h*_{a}(*T*) is the specific enthalpy of the dry air.*h*_{a}(*T*_{w}) is the specific enthalpy of the dry air at the wet bulb temperature.*h*_{g}(*T*) is the specific enthalpy of the trace gas.*h*_{g}(*T*_{w}) is the specific enthalpy of the trace gas at the wet bulb temperature.*h*_{w}(*T*) is the specific enthalpy of the water vapor.*h*_{w}(*T*_{w}) is the specific enthalpy of the water vapor at the wet bulb temperature.*Δh*_{fg}(*T*_{w}) is the specific enthalpy of vaporization of water vapor at the wet-bulb temperature.

## Ports

### Conserving

## Parameters

## Extended Capabilities

## Version History

**Introduced in R2018a**