Controlled Mass Flow Rate Source (MA)
A source of mass or volumetric flow.
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Description
The Flow Rate Source (MA) unit represents an ideal source of mechanical energy in a humid air network. The source can maintain a given mass or volume flow rate regardless of pressure drop. There is no flow resistance and no heat exchange with the environment.
A positive flow rate causes moist air to flow from port A to port B. If Controlled source is enabled, the mass or volume flow rate is controlled by the input signal at ports M or V respectively. If Controlled source is disabled, the mass or volumetric flow rate is controlled by Mixture mass flow rate or Mixture volumetric flow rate respectively.
Volumetric flow rate and mass flow rate are related by the expression:
where:
-
- is the mass flow rate from port A to port B.
-
and are the densities at ports A and B respectively.
-
- volumetric flow rate.
Lower indices and indicate the corresponding port.
Mass conservation
,
,
,
Where:
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- mass flow rate.
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Lower indices and are ports A and B respectively.
-
Lower indices and indicate water vapour and gas impurity properties respectively.
Energy balance
,
where and are the energy flow through ports A and B respectively.
If the source does not perform any work (for the Isentropic power added parameter switched off), then .
If the source is isentropic (for the Isentropic power added parameter turned on), then:
where:
The enthalpies of the mixtures, and , are bounded by isoentropic dependence, i.e., there is no entropy change:
If Flow type is set to `Mass' and Controlled source is unchecked, the mass flow rate is determined by Mixture mass flow rate and is equal to
Ports
A - source inlet
`moist air
Moist air port. Positive mass flow rate causes moist air to flow from port A to port B.
B is the source outlet
`humid air
Moist Air Port. Positive mass flow rate causes moist air to flow from port A to port B.
M - mass flow rate control signal, kg/sec
scalar
Input port that determines the mass flow rate of moist air through the source.
Dependencies
Used when the Controlled source checkbox is selected and the Flow type parameter is set to Mass.
V - volumetric flow rate control signal, m³/s
scalar
Input port that determines the volumetric flow rate of moist air through the source.
Dependencies
Used when Controlled source is checked and Flow type is set to `Volumetric'.
Parameters
Controlled source - whether the flow rate is set by the input signal
On (by default) | Off
Defines how the flow rate will be set:
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`On' - mass or volume flow rate is set by input signals on M or V ports, respectively.
-
Disabled - mass or volumetric flow rate is set by Mixture mass flow rate or Mixture volumetric flow rate respectively.
Flow type - mass or volumetric flow rate
Mass (By default) | Volumetric.
Determines which flow type is specified:
-
Mass- mass flow rate is set. -
Volumetric' - sets the volumetric flow rate.
Isentropic power added - whether the source performs isentropic work
On (by default) | Off
Sets whether the source performs isentropic work with moist air flow:
-
`On' - the source performs isoentropic work with moist air to maintain the specified mass or volume flow rate. Use this parameter to represent an ideal pump or compressor and to properly account for energy input and output, especially in closed loop systems.
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`Off' - the source does not perform any work on the flow, either adding or removing power, regardless of the mass or volumetric flow rate generated by the source. Use this option to set the desired flow condition upstream of the system without affecting the flow temperature.
Mixture mass flow rate - constant mass flow rate through the source
0 (By default).
Constant mass flow rate of moist air through the source.
Dependencies
Used when Controlled source is unchecked and Flow type is set to Mass.
Mixture volumetric flow rate - constant volumetric flow rate through the source
0 (By default).
Constant volumetric flow rate of moist air through the source.
Dependencies
Used when Controlled source is unchecked and Flow type is set to `Volumetric'.
Specified flow rate conditions - conditions for calculating the volumetric flow rate
Actual conditions (By default) | Standard conditions.
Specifies whether the source calculates the volumetric flow rate under actual operating conditions or at standard pressure, temperature and relative humidity:
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`Actual conditions' - the source calculates the volumetric flow rate using the density of moist air under actual system conditions.
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`Standard conditions' - the source calculates the volumetric flow rate using the density of moist air under standard conditions.
Dependencies
Used when Flow type is set to Volumetric.
Standard pressure - moist air pressure at standard conditions
`0.101325 MPa (by default).
Humid air pressure at standard conditions.
Dependencies
Used when Flow type is set to Volumetric and Specified flow rate conditions is set to Standard conditions.
Standard Temperature is the wet air temperature under standard conditions
`20 °C (by default).
Humid air temperature under standard conditions.
Dependencies
Used when Flow type is set to `Volumetric' and Specified flow rate conditions is set to `Standard conditions'.
Standard relative humidity - relative humidity under standard conditions
0.65 (By default).
Relative humidity at standard conditions.
Dependencies
Used when Flow type is set to Volumetric and Specified flow rate conditions is set to Standard conditions.
Cross-sectional area at port A - cross-sectional area normal to the flow path at port A
0.01 m² (by default).
Cross-sectional area normal to the flow path at port A.
Cross-sectional area at port B - cross-sectional area normal to the flow path at port B
`0.01 m² (by default).
Cross-sectional area normal to the flow path at port B.