This model describes the mass flow rate and pressure difference
relation of an orifice in the form

V̇ = k
Δp^{m},

where *V̇* is the volume flow rate, *k* is a flow
coefficient and *m* is the flow exponent. The flow coefficient
is

k = 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
crack-like 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.

- 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 non-backward 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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