Hydraulics and Fluid Mechanics in ME
An orifice is said to be large, if

The size of orifice is large
The available head of liquid is more than 5 times the height of orifice
The velocity of flow is large
The available head of liquid is less than 5 times the height of orifice

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Hydraulics and Fluid Mechanics in ME
Froude number is significant in

Simultaneous motion through two fluids where there is a surface of discontinuity, gravity forces, and wave making effect, as with ship's hulls
Full immersion or completely enclosed flow, as with pipes, aircraft wings, nozzles etc.
Supersonics, as with projectile and jet propulsion
All of the listed here

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