Flow Resistance (MA)
Generalized resistance in the humid air network.
blockType: AcausalFoundation.MoistAir.Elements.FlowResistance
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Path in the library: |
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Description
Block Flow Resistance (MA) simulates the total pressure drop in the humid air network. The pressure drop is proportional to the square of the mass flow and inversely proportional to the density of the humid air. The proportionality coefficient is determined based on the nominal operating condition specified in the unit parameters.
This block is used when only the pressure drop depending on the mass flow rate is known about the component and there is no detailed information about the geometry.
Conservation of mass:
where
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— mass consumption;
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Lower indexes and — ports A and B respectively;
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Lower indexes , and They indicate the properties of water vapor, gas impurities, and water droplets, respectively.
Energy balance:
where and — energy flow through ports A and B respectively.
If the parameter value is Nominal density, , is greater than zero, then the block calculates the pressure drop as:
where
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and — pressure at ports A and B, respectively;
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— mass flow rate for laminar-turbulent transition;
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— inlet pressure ( and depending on the direction of the current);
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— inlet temperature ( and depending on the direction of the current);
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— proportionality coefficient calculated on the basis of nominal values:
If the parameter value is Nominal density, , is equal to zero, then the block calculates the pressure drop as:
where — proportionality coefficient:
The flow resistance is considered adiabatic, so the specific total enthalpy of the mixture is equal to:
Ports
Conserving
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B
—
input or output
moist air
Details
Wet air port, corresponds to the input or output of the generalised resistance. This block has no defined directionality.
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A
—
input or output
moist air
Details
Wet air port, corresponds to the input or output of the generalised resistance. This block has no defined directionality.
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Parameters
Main
#
Cross-sectional area at A and B —
flow area at the ports of generalised resistance
m^2 | um^2 | mm^2 | cm^2 | km^2 | in^2 | ft^2 | yd^2 | mi^2 | ha | ac
Details
Flow area at the ports of generalised resistance. It is assumed that the ports are identical in size.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Nominal pressure drop —
pressure drop at known operating conditions
Pa | uPa | hPa | kPa | MPa | GPa | kgf/m^2 | kgf/cm^2 | kgf/mm^2 | mbar | bar | kbar | atm | ksi | psi | mmHg | inHg
Details
Pressure drop from inlet to outlet at known operating mode. The unit uses nominal parameters to calculate the proportionality factor between pressure drop and mass flow rate.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Fraction of nominal mass flow rate for laminar flow transition — the ratio of the threshold flow rate to the nominal mass flow rate
Details
The ratio of the threshold mass flow rate to the nominal mass flow rate. The unit uses this parameter to calculate the mass flow threshold and to set the linearisation limits for the differential pressure.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
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Nominal density —
density at known operating conditions
kg/m^3 | g/m^3 | g/cm^3 | g/mm^3 | lbm/ft^3 | lbm/gal | lbm/in^3
Details
Mass density within the generalised resistance at known operating mode. The unit uses nominal parameters to calculate the coefficient of proportionality between pressure drop and mass flow rate. Set this parameter to zero to ignore the dependence of pressure drop on wet air density.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Nominal mass flow rate —
mass flow rate at known operating mode
kg/s | kg/hr | kg/min | g/hr | g/min | g/s | t/hr | lbm/hr | lbm/min | lbm/s
Details
Mass flow rate from inlet to outlet at known operating mode. The unit uses nominal parameters to calculate the proportionality factor between pressure drop and mass flow rate.
| Units |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |