This pressure drop component defines a
simple, generic orifice, where the loss factor ζ is provided
for one flow direction (e.g., from loss table of a book):
Δp = 0.5*ζ*ρ*v*|v|
= 8*ζ/(π^2*D^4*ρ) * m_flow*|m_flow|
where
- Δp is the pressure drop: Δp = port_a.p - port_b.p
- D is the diameter of the orifice at the position where
ζ is defined (either at port_a or port_b). If the orifice has not a
circular cross section, D = 4*A/P, where A is the cross section
area and P is the wetted perimeter.
- ζ is the loss factor with respect to D
that depends on the geometry of
the orifice. In the turbulent flow regime, it is assumed that
ζ is constant.
For small mass flow rates, the flow is laminar and is approximated
by a polynomial that has a finite derivative for m_flow=0.
- v is the mean velocity.
- ρ is the upstream density.
Since the pressure loss factor zeta is provided only for a mass flow
from port_a to port_b, the pressure loss is not correct when the
flow is reversing. If reversing flow only occurs in a short time interval,
this is most likely uncritical. If significant reversing flow
can appear, this component should not be used.
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