# Interface (G-MA)

Gas and moist air network interface

• Library:
• Simscape / Fluids / Fluid Network Interfaces

• ## Description

The Interface (G-MA) block represents a flow connection between a gas network and moist air network. Pressure, temperature, and mass flow rate are equal at the interface. The block does not transfer the fluid properties of each fluid network across the interface. To conserve fluid properties, ensure that the Gas Properties (G) block and the Moist Air Properties (MA) block have the same settings. When moist air leaves port MA, the block assigns the values of the Interface specific humidity and Interface trace gas mass fraction parameters to the signal. However, when moist air enters port MA, the block retains the upstream values.

You can choose whether to maintain constant moisture and trace gas amounts at the interface or to specify them using the W and TG ports, respectively.

### Mass and Momentum Balance

The block conserves mass such that

`${\stackrel{˙}{m}}_{G}+{\stackrel{˙}{m}}_{MA}=0,$`

where:

• G is the mass flow rate into port G.

• MA is the mass flow rate into port MA.

The block maintains equal port pressures and temperatures such that

`$\begin{array}{l}{p}_{G}={p}_{MA}\\ {T}_{G}={T}_{MA}\end{array}$`

### Energy Balance

The block calculates the energy balance over the interface as

`${\Phi }_{G}+{\Phi }_{MA}={\stackrel{˙}{m}}_{G}\left({h}_{G}+\frac{{w}_{G}^{2}}{2}\right)+{\stackrel{˙}{m}}_{MA}\left({h}_{MA}+\frac{{w}_{MA}^{2}}{2}\right),$`

where:

• ΦG is the energy flow rate into port G.

• ΦMA is the energy flow rate into port MA.

• hG is the specific enthalpy at port G.

• hMA is the specific enthalpy at port MA.

• vG is the specific volume at port G.

• vMA is the specific volume at port MA.

• wG is the flow velocity at port G.

• wMA is the flow velocity at port MA.

For a given cross-sectional area, S, the block defines wG as

`${w}_{G}=\frac{{\stackrel{˙}{m}}_{G}{v}_{G}}{S},$`

and wMA as

`${w}_{MA}=\frac{{\stackrel{˙}{m}}_{MA}{v}_{MA}}{S},$`

where:

`${v}_{MA}=\frac{{R}_{I}{T}_{MA}}{{p}_{MA}}.$`

The specific gas constant of the mixture at the interface is a function of the fluid on either side such that

`${R}_{I}=f\left({R}_{A},{R}_{W}{R}_{G},{x}_{WI},{x}_{GI}\right),$`

where:

• RA is the dry air specific gas constant.

• RW is the water vapor specific gas constant.

• RG is the trace gas specific gas constant.

• xWI is the interface specific humidity. The upstream moist air network assigns this value when flow enters port MA. When the flow exits port MA, the block assigns this value based on the value of the Interface relative humidity parameter or the input that you supply at port W.

• xGI is the interface trace gas mass fraction. The upstream moist air network assigns this value when flow enters port MA. When the flow exits port MA, the block assigns this value based on the value of the Interface trace gas mass fraction parameter or the input that you supply at port TG.

## Ports

### Conserving

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Gas conserving port associated with the gas at the interface.

Moist air conserving port associated with the moist air at the interface.

Physical signal port associated with the moisture content at the interface.

#### Dependencies

To enable this port, set Interface type to `Controlled`.

Physical signal port associated with the trace gasses at the interface.

#### Dependencies

To enable this port, set Interface type to `Controlled`.

## Parameters

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Option to maintain a constant interface or to specify the moisture and trace gas amounts via physical signal ports. When you select `Controlled`, the block exposes the W and TG ports.

Whether to calculate moisture using relative humidity, specific humidity, mole fraction, or humidity ratio.

Relative humidity at the interface. The block uses this value to calculate the moisture.

#### Dependencies

To enable this parameter, set Interface type to `Constant` and Moisture specification to ```Relative humidity```.

Specific humidity at the interface. The block uses this value to calculate the moisture.

#### Dependencies

To enable this parameter, set Interface type to `Constant` and Moisture specification to ```Specific humidity```.

Water vapor mole fraction at the interface. The block uses this value to calculate the moisture.

#### Dependencies

To enable this parameter, set Interface type to `Constant` and Moisture specification to ```Mole fraction```.

Humidity ratio at the interface. The block uses this value to calculate the moisture.

#### Dependencies

To enable this parameter, set Interface type to `Constant` and Moisture specification to ```Humidity ratio```.

Whether to parameterize the trace gas at the interface using mass fraction or mole fraction.

Mass fraction of trace gas at the interface.

#### Dependencies

To enable this parameter, set Interface type to `Constant` and Interface trace gas specification to ```Mass fraction```.

Mole fraction of trace gas at the interface.

#### Dependencies

To enable this parameter, set Interface type to `Constant` and Interface trace gas specification to ```Mole fraction```.

Relative humidity at the point of saturation.

Cross-sectional area of the gas and moist air ports.

Monitor or control invalid inputs. When you select ```Limit to valid values```, the block saturates the inputs within the bounds. You can choose to have the block issue a warning when it limits the inputs by selecting ```Warn and limit to valid values```, or you can stop the simulation when the block receives invalid inputs by selecting `Error`.

#### Dependencies

To enable this parameter, set Interface type to `Controlled`.

## Version History

Introduced in R2022a