From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page discussing the coefficients of velocity and contraction for fluid flow through orifices, including Borda's mouthpiece.
| Identifier | ExFiles\Box 36\1\ scan 014 | |
| Date | 15th February 1916 | |
| R.R. 22A A (400 T) (S.C. 536. 15-2-16) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 1646. -2- Contd. Cv is always very nearly unity, generally .97 or .98 with no shock loss for simple orifices, and is very slightly greater for very great heads. Conditions tending to modify the value of Cc :- The least value of Cc i.e. the greatest contraction, occurs in the case of an inwardly projecting orifice called Borda's mouthpiece. The ideal minimum value of Cc is .5 exactly and the measured value for this case is about .534. Sharp edged orifices have coefficients of contraction averaging .63 provided the orifice is not near the side or bottom of the vessel. But (1) The contraction is imperfect and will be suppressed over the lower edge of the orifice if placed at the bottom of the tank, and over the side as well as the bottom if the orifice is in the corner. In fact, contraction is more or less imperfect for any orifice within three diameters of the side or bottom of the tank. Thus the cross section of the contracted vein is increased and experiment shows that the discharge is also increased. (2) Cc is increased or diminished according as the surface surrounding the orifice is convex or concave to the interior of the vessel. | ||