Flow Resistance (IL)
Hydraulic resistance.
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Description
The Flow Resistance (IL) block represents the pressure drop in an isothermal liquid line. The pressure drop is proportional to the square of the mass flow rate.
Use this block when only the flow rate and pressure drop are known for a component. This block is useful for representing complex components where it is difficult to determine the theoretical pressure drop from geometric constructions.
Assume that the volume of fluid inside the resistance is negligibly small. Then the mass flow rate at the inlet through one port must exactly equal the mass flow rate at the outlet through the other port:
where and are defined as the mass flow rates through ports A and B, respectively.
The pressure drop is assumed to be proportional to the square of the mass flow rate. The square of the mass flow rate is linearised in a small laminar flow region near zero flow, resulting in the following
,
where:
-
and are pressures at ports A and B, respectively.
-
- threshold value of mass flow rate for laminar-turbulent transition.
- proportionality coefficient:
,
where is the value of parameter Nominal pressure drop and is the value of parameter Nominal mass flow rate.
Ports
Non-directional
A - inlet or outlet port
isothermal liquid
The isothermal liquid port represents the inlet or outlet of the hydraulic resistance. This unit has no internal directionality.
B - inlet or outlet port
isothermal liquid
The isothermal liquid port represents the inlet or outlet of the hydraulic resistance. This unit has no internal directionality.
Parameters
Nominal pressure drop, Pa - pressure drop at known operating mode
1000.0 Pa (by default)
Pressure drop from inlet to outlet at known operating mode. The unit uses the nominal parameters to calculate the coefficient of proportionality between differential pressure and mass flow rate.
Nominal mass flow rate, kg/s - mass flow rate at known operating mode
0.1 kg/s (By default).
Mass flow rate at known operating mode. The unit uses nominal parameters to calculate the proportionality factor between pressure drop and mass flow rate.
Fraction of nominal mass flow rate for laminar flow - ratio of threshold flow rate to nominal mass flow rate
1e-3 (by default)
Ratio of threshold mass flow rate to nominal mass flow rate. The unit uses this parameter to calculate the threshold mass flow rate - and ultimately to set the linearisation limits for the differential pressure.