Engee documentation

Reservoir (MA)

Boundary conditions for a network of moist air at constant pressure, temperature, humidity and amount of impurity gases.

blockType: AcausalFoundation.MoistAir.Elements.Reservoir

reservoir (ma)

Path in the library:

/Physical Modeling/Fundamental/Moist Air/Elements/Reservoir (MA)

Description

The Reservoir (MA) unit represents an infinite reservoir at fixed pressure, temperature, humidity and amount of impurity gases. The reservoir and its inlet can be at atmospheric or set pressure. Port A corresponds to the inlet of the tank. The volume of moist air inside the tank is assumed to be infinite, so the flow is assumed to be quasi-stationary.

Humid air enters and leaves the tank at the pressure specified for the tank, the other characteristics of the humid air (temperature, specific humidity and mass fraction of impurity gases) are determined by the direction of the humid air flow:

  • If the moist air leaves the tank, its temperature, specific humidity and mass fraction of impurity gases are equal to the corresponding tank parameters.

  • If humid air enters the tank, its temperature, specific humidity and mass fraction of impurity gases are determined by the previous network of humid air.

Humidity can be measured as one of the values:

  • Relative humidity, - relative humidity, parameter Reservoir relative humidity.

  • Specific humidity, - specific humidity, parameter Reservoir specific humidity.

  • `Water vapor mole fraction', - water vapour molar fraction, parameter Reservoir water vapor mole fraction.

  • Humidity ratio, - humidity ratio, parameter Reservoir humidity ratio.

  • Wet-bulb temperature, - wet-bulb temperature, parameter Reservoir wet-bulb temperature.

You can specify the impurity gas as one of the following parameters:

  • Mass fraction , - impurity gas mass fraction, parameter Reservoir trace gas mass fraction.

  • `Mole fraction', - molar fraction of impurity gas, parameter Reservoir trace gas mole fraction.

The amount of moisture and impurity gas are related to each other as follows:

Where:

  • - pressure.

  • - is the universal gas constant.

The subscripts , and denote the properties of dry air, water vapour and impurity gas, respectively. The subscript denotes water vapour at saturation.

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

Where:

  • - temperature.

  • - is the wet-bulb temperature.

  • - specific humidity.

  • - mass fraction of impurity gas.

  • - saturation specific humidity at wet-bulb temperature.

  • - specific enthalpy of dry air.

  • - specific enthalpy of dry air at wet-bulb temperature.

  • - specific enthalpy of impurity gas.

  • - specific enthalpy of impurity gas at wet-bulb temperature.

  • - specific enthalpy of water vapour.

  • - specific enthalpy of water vapour at wet thermometer temperature.

  • - specific enthalpy of vaporisation of water vapour at wet-bulb temperature.

Ports

Non-directional

A - humid air port
`humid air

Humid air port, corresponds to the tank inlet.

Parameters

Reservoir pressure specification - pressure specification method
Atmospheric pressure (by default) | Specified pressure

Select the pressure specification method:

  • Atmospheric pressure - atmospheric pressure is used.

  • Specified pressure - the value of the Reservoir pressure parameter is used.

Reservoir pressure - pressure in the reservoir
0.101325 MPa (by default)

Sets the pressure in the reservoir. This pressure remains constant throughout the simulation.

Dependencies

Used when Reservoir pressure specification is set to Specified temperature.

Reservoir temperature specification - temperature specification method
Atmospheric temperature (by default) | Specified pressure.

Select the temperature reference method:

  • Atmospheric temperature - atmospheric temperature is used.

  • Specified temperature - the value of the Reservoir temperature parameter is used.

*Reservoir temperature - the temperature in the reservoir
`293.15 K (by default).

Sets the temperature in the reservoir. This temperature remains constant for the duration of the simulation.

Dependencies

Used when Reservoir temperature specification is set to Specified temperature.

Reservoir moisture specification - how moisture is measured
Relative humidity (By default) | Specific humidity | Water vapor mole fraction | Humidity ratio | Wet-bulb temperature.

Sets the method of measurement:

  • Relative humidity - moisture composition is specified via relative humidity by the Reservoir relative humidity parameter.

  • Specific humidity - the moisture content is specified through specific humidity by Reservoir specific humidity.

  • Water vapor mole fraction - moisture composition is specified through molar fraction of moisture by Reservoir water vapor mole fraction.

  • Humidity ratio - the moisture composition is specified through the humidity ratio by the Reservoir humidity ratio parameter.

  • Wet-bulb temperature - the moisture content is specified through the wet-bulb temperature by Reservoir wet-bulb temperature.

Reservoir relative humidity - relative humidity in the reservoir
0.5 (by default)

Sets the relative humidity value in the reservoir. This value remains constant during the simulation.

Dependencies

Used when Reservoir moisture specification is set to Relative humidity.

Reservoir specific humidity - specific humidity in the reservoir
0.01 (By default).

Sets the value of specific humidity in the reservoir. This value remains constant during the simulation.

Dependencies

Used when Reservoir moisture specification is set to Specific humidity.

Reservoir water vapour mole fraction - molar fraction of water vapour in the reservoir.
0.01 (By default).

Enter the desired reservoir water vapour mole fraction. This value remains constant during the simulation.

Dependencies

Used when Reservoir moisture specification is set to `Mole fraction'.

Reservoir humidity ratio - reservoir humidity ratio
`0.01 (By default).

Sets the value of relative humidity in the reservoir. This value remains constant during the simulation.

Dependencies

It is used when the Reservoir moisture specification is set to `Humidity ratio'.

Reservoir wet-bulb temperature - wet-bulb temperature of the reservoir thermometer
287 K (By default).

Enter the desired reservoir wet-bulb temperature. This value remains constant during the simulation.

Dependencies

Used when the Reservoir moisture specification is set to Wet-bulb temperature.

Reservoir trace gas specification - how to measure the amount of trace gas
Mass fraction (by default) | `Mole fraction'.

Sets the measurement method:

  • Mass fraction - impurity gas mass fraction set by the Reservoir trace gas mass fraction parameter.

  • `Mole fraction' - the molar fraction of impurity gases is set by Reservoir trace gas mole fraction.

Reservoir trace gas mass fraction - mass fraction of impurity gas in the reservoir
0.001 (by default)

Enter the desired reservoir trace gas mass fraction. This value remains constant during the simulation.

Dependencies

Used when the Reservoir trace gas specification is set to `Mass fraction'.

Reservoir trace gas mole fraction - molar fraction of impurity gas
0.001 (By default).

Enter the desired reservoir trace gas mole fraction. This value remains constant during the simulation.

Dependencies

Used when the Reservoir trace gas specification is set to `Mole fraction'.

Relative humidity at saturation - relative humidity above which condensation occurs
1.0 (By default).

Relative humidity above which condensation occurs. The amount of moisture must be less than the saturation level.

Cross-sectional area at port A - area normal to the direction of flow at the tank inlet
`0.01 m² (by default)

The cross-sectional area of the tank inlet in the direction normal to the wet air flow path.

Examples