Interface (G-MA)

Gas and moist air network interface

Since R2022a

• 

Libraries:
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 relative humidity, Interface trace gas mass fraction, and Interface mass ratio of water droplets to moist air parameters, or the values of the input signals, to the signal. However, when moist air enters port MA, the block retains the upstream values.

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

Mass and Momentum Balance

The block conserves mass such that

$${\dot{m}}_G+{\dot{m}}_{MA}=0,$$

where:

• ṁ_G is the mass flow rate into port G.

• ṁ_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

$${\Phi }_G+{\Phi }_{MA}={\dot{m}}_G\left(h_G+\frac{w_G^2}{2}\right)+{\dot{m}}_{MA}\left(h_{MA}+\frac{w_{MA}^2}{2}\right),$$

where:

• Φ_G is the energy flow rate into port G.

• Φ_MA is the energy flow rate into port MA.

• h_G is the specific enthalpy at port G.

• h_MA is the specific enthalpy at port MA.

• v_G is the specific volume at port G.

• v_MA is the specific volume at port MA.

• w_G is the flow velocity at port G.

• w_MA is the flow velocity at port MA.

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

$$w_G=\frac{{\dot{m}}_G{v}_G}{S},$$

and w_MA as

$$w_{MA}=\frac{{\dot{m}}_{MA}{v}_{MA}}{S},$$

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:

• R_A is the dry air specific gas constant.

• R_W is the water vapor specific gas constant.

• R_G is the trace gas specific gas constant.

• x_WI is the interface specific humidity. The block determines this value when the flow exits port MA, based on your parameter settings:

  • When you clear the Provide input signal for interface humidity check box, the block calculates x_WI based on the method specified with the Interface humidity specification parameter.

  • When you select Provide input signal for interface humidity, the block bases x_WI on the input that you supply at port W or port Tw.

• x_GI is the interface trace gas mass fraction. The block determines this value when the flow exits port MA, based on your parameter settings:

  • When you clear the Provide input signal for interface trace gas check box, the block calculates x_GI based on the value of the Interface trace gas mass fraction or Interface trace gas mole fraction parameter.

  • When you select Provide input signal for interface trace gas, the block bases x_GI on the input that you supply at port TG.

Ports

Input

W — Humidity, unitless

physical signal

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

Dependencies

To enable this port, select Provide input signal for interface humidity and set Interface humidity specification to Relative humidity, Specific humidity, Mole fraction, or Humidity ratio.

Tw — Temperature, K

physical signal

Physical signal port associated with the wet-bulb temperature at the interface, in K.

Dependencies

To enable this port, select Provide input signal for interface humidity and set Interface humidity specification to Wet-bulb temperature.

TG — Trace gas, unitless

physical signal

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

Dependencies

To enable this port, select Provide input signal for interface trace gas.

D — Water droplet mass ratio, unitless

physical signal

Physical signal port associated with the mass ratio of water droplets to moist air at the interface.

Dependencies

To enable this port, select Provide input signal for interface water droplets.

Conserving

G — Fluid port

gas

Gas conserving port associated with the gas at the interface.

MA — Moist air port

moist air

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

Parameters

Provide input signal for interface humidity — Interface humidity control option

off (default) | on

Option for specifying the interface humidity. If you select this check box, the block enables port W. If you clear this check box, you can specify constant humidity conditions.

Interface humidity specification — Humidity parameterization option

Relative humidity (default) | Specific humidity | Mole fraction | Humidity ratio | Wet-bulb temperature

Whether to calculate humidity using relative humidity, specific humidity, mole fraction, humidity ratio, or wet-bulb temperature.

Interface relative humidity — Relative humidity at interface

0.5 (default) | positive scalar

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

Dependencies

To enable this parameter, clear the Provide input signal for interface humidity check box and set Interface humidity specification to Relative humidity.

Interface specific humidity — Specific humidity at interface

0.01 (default) | positive scalar

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

Dependencies

To enable this parameter, clear the Provide input signal for interface humidity check box and set Interface humidity specification to Specific humidity.

Interface water vapor mole fraction — Water vapor mole fraction at interface

0.01 (default) | positive scalar

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

Dependencies

To enable this parameter, clear the Provide input signal for interface humidity check box and set Interface humidity specification to Mole fraction.

Interface humidity ratio — Humidity ratio at interface

0.01 (default) | positive scalar

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

Dependencies

To enable this parameter, clear the Provide input signal for interface humidity check box and set Interface humidity specification to Humidity ratio.

Interface wet-bulb temperature — Wet-bulb temperature at interface

287 K (default) | positive scalar

Wet bulb temperature at the interface. The block uses this value to calculate humidity.

Dependencies

To enable this parameter, clear the Provide input signal for interface humidity check box and set Interface humidity specification to Wet-bulb temperature.

Provide input signal for interface trace gas — Interface trace gas control option

off (default) | on

Option for specifying the trace gas fraction. If you select this check box, the block enables port TG. If you clear this check box, you can specify constant trace gas conditions.

Interface trace gas specification — Trace gas parameterization

Mass fraction (default) | Mole fraction

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

Interface trace gas mass fraction — Trace gas mass fraction at interface

0.001 (default) | positive scalar

Mass fraction of trace gas at the interface.

Dependencies

To enable this parameter, clear the Provide input signal for interface trace gas check box and set Interface trace gas specification to Mass fraction.

Interface trace gas mole fraction — Trace gas mole fraction at interface

0.001 (default) | positive scalar

Mole fraction of trace gas at the interface.

Dependencies

To enable this parameter, clear the Provide input signal for interface trace gas check box and set Interface trace gas specification to Mole fraction.

Provide input signal for interface water droplets — Interface water droplet control option

off (default) | on

Option for specifying the mass ratio of water droplets to moist air. If you select this check box, the block enables port D. If you clear this check box, you can specify constant water droplet conditions with the Interface mass ratio of water droplets to moist air parameter.

Interface mass ratio of water droplets to moist air — Ratio of water droplets to moist air at interface

0 (default) | positive scalar

Mass ratio of water droplets to moist air at the interface.

Dependencies

To enable this parameter, clear the Provide input signal for interface water droplets check box.

Relative humidity at saturation — Saturation point relative humidity

1 (default) | positive scalar

Relative humidity at the point of saturation.

Cross-sectional area at ports G and MA — Port area

0.01 m^2 (default) | positive scalar

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

Inputs outside valid range — Option to monitor or control invalid inputs

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

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.

Extended Capabilities

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

Version History

Introduced in R2022a

R2024b: Model water droplets suspended in moist air flow

Blocks in the moist air domain can now model water droplets suspended in a moist air flow. To enable droplet tracking, select Enable entrained water droplets in the Moist Air Properties (MA) block connected to your moist air network.

Instead of using the Moisture and trace gas specification parameter to specify whether the interface is constant or controlled, use the new Provide input signal for interface humidity, Provide input signal for interface trace gas, and Provide input signal for interface water droplets parameters to enable the physical signal input ports.

R2023a: New moisture specification option

The block has a new option for the Interface humidity specification parameter. This option, called Wet-bulb temperature, allows you to input data in the form of a wet-bulb temperature.