Controlled Pressure Difference Source (MA)
Source of differential pressure.
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Description
The Pressure Difference Source (MA) unit represents an ideal source of mechanical energy in a wet air network. The source can maintain a constant or variable pressure differential at its ports regardless of the mass flow rate through the source. There is no gas resistance and no heat exchange with the environment. A positive value of the differential pressure causes the pressure at port B to be greater than the pressure at port A.
Conservation of mass
,
,
,
Where:
-
- mass flow rate.
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The lower indices and indicate 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:
The value given by the parameter Pressure differential or the input signal P of the source is:
Ports
Non-directional
A - source inlet
`humid air
Moist air port. Positive pressure drop causes the pressure at port B to be greater than the pressure at port A.
B is the source inlet
`humid air
Moist air port. Positive pressure drop causes the pressure at port B to be greater than the pressure at port A.
Inlet
P - differential pressure set point signal, Pa
scalar
Input port that defines the pressure differential of the humid air in the source. A positive signal at port P causes the pressure at port B to be greater than the pressure at port A.
Dependencies
To use this port, select the Controlled source checkbox.
Parameters
Controlled source - whether differential pressure is set by the input signal
On (by default) | Off
Defines how the differential pressure will be set:
-
`On' - differential pressure is set by input signal P.
-
Disabled - constant differential pressure is set by the Pressure differential parameter.
Isentropic power added - whether the source performs isentropic work
On (by default) | Disabled
Sets whether the source performs isentropic work with moist air flow:
-
`On' - the source performs isoentropic work with moist air to maintain the specified pressure drop. 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 pressure drop generated by the source. Use this option to set the desired flow condition upstream of the system without affecting the flow temperature.
Pressure differential - constant pressure differential
0 (By default).
Pressure differential of the humid air mixture at the source ports.
Dependencies
Used if the Controlled source checkbox is not selected.
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.