This model describes the mass flow rate and pressure difference relation
of an orifice in the form
V̇ = C Δp^{m},
where
V̇ is the volume flow rate,
C is a flow coefficient and
m is the flow exponent.
The flow coefficient is
C = C_{D} A (2/ρ_{0})^{0.5},
where
C_{D} is the discharge coefficient,
A is the cross section area and
ρ_{0} is the mass density at the medium default pressure, temperature and humidity.
For turbulent flow, set m=1/2 and
for laminar flow, set m=1.
Large openings are characterized by values close to 0.5,
while values near 0.65 have been found for small
cracklike openings (Dols and Walton, 2002).
References

W. Stuart Dols and George N. Walton, CONTAMW 2.0 User Manual,
Multizone Airflow and Contaminant Transport Analysis Software,
Building and Fire Research Laboratory,
National Institute of Standards and Technology,
Tech. Report NISTIR 6921,
November, 2002.
 Michael Wetter.
Multizone Airflow Model in Modelica.
Proc. of the 5th International Modelica Conference, p. 431440. Vienna, Austria, September 2006.

February 2, 2022, by Michael Wetter:
Revised implementation.
This is for
IBPSA, #1436.

Apr 6, 2021, by Klaas De Jonge:
Changes due to changes in the baseclass, velocity is now a toplevel variable.

June 27, 2018, by Michael Wetter:
Corrected old parameter annotation.

June 24, 2018, by Michael Wetter:
Removed parameter lWet
as it is only used to compute
the Reynolds number, and the Reynolds number is not used by this model.
Also removed the variable Re
for the Reynolds number.
This change is nonbackward compatible.
This is for
IBPSA, #932.

May 30, 2018, by Michael Wetter:
Improved documentation for
IBPSA, #546.

October 8, 2013 by Michael Wetter:
Changed the parameter useConstantDensity
to
useDefaultProperties
to use consistent names within this package.
A conversion script can be used to update this parameter.

December 6, 2011 by Michael Wetter:
Replaced rho
with rho_nominal
because
rho
is computed in an equation
section and not
in the initial equation
section.

July 20, 2010 by Michael Wetter:
Migrated model to Modelica 3.1 and integrated it into the Buildings library.

February 4, 2005 by Michael Wetter:
Released first version.
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