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

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

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Hydraulics and Fluid Mechanics in ME
Froude number is significant in

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
Simultaneous motion through two fluids where there is a surface of discontinuity, gravity forces, and wave making effect, as with ship's hulls

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Hydraulics and Fluid Mechanics in ME
Coefficient of contraction is the ratio of

Actual velocity of jet at vena contracta to the theoretical velocity
Loss of head in the orifice to the head of water available at the exit of the orifice
Loss of head in the orifice to the head of water available at the exit of the orifice
Area of jet at vena-contracta to the area of orifice

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