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BACKGROUND
An orifice is a small aperture which is the small opening in a wall tank through which the fluid passes. If the length of the tank is less than two to three times of the diameter of orifice, then mouthpiece is also used in the set-up. The jet passing through the orifice converges parallel to the streamline at a section of the minimum area, which is known as vena contracta.1
Coefficient of velocity is the ratio actual jet velocity at vena-contracta to its theoretical velocity.
i.e, Cv = {(Actual jet velocity at vena contracta / Theoretical velocity)},
or, Cv = {X / 2(Y.h)1/2}
where, h = constant head
X, Y = coordinates of the jet with respect to centre of the opening.2
Whereas the discharge coefficient is the ratio of actual discharge to the theoretical discharge.
Hence, Cd = (Qactual / Qtheoretical),
Or, Cd = {Qactual / a.(2gh)1/2}
Here, a = Area of the cross-section of the orifice,
g = acceleration due to gravity.
The experimental set-up consists of a supply tank with orifice and mouthpiece connected to it, and this also contains an overflow arrangement as well as gauge glass tube. The water will pass only through the attached opening in this set-up, and it comes out through the orifice in a streamlined jet form.3
The main purpose of this experiment is to determine the coefficient of velocity (Cv), and discharge coefficient (Cd) of an orifice.
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REQUIREMENTS
Materials: Supply tank with overflow arrangement
Orifice (10 mm dia.)
Scale
Sliding apparatus with hook gauge
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PROCEDURE
First of all, set the mouthpiece of the orifice on the tank to which the coefficient values are to be determined. Now, note the initial height of water in a steady state from the datum point and the bottom of an orifice. These values will remain constant for a particular orifice or mouthpiece in an experiment. After this, set a specific flow in the tank by using a stop valve, and note down the discharge reading on a particular stream. Note down the X and Y coordinate values by using a hook gauge. Alas, calculate the value of Cv and Cd by using formula.
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CONCLUSION
The procedure of determining the coefficient of velocity and discharge coefficient has been discussed. Both of these values depend on the constant head (h).
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REFERENCES
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R. B. G. S. Duqiang Wu, “An Empirical Discharge Coefficient Model for Orifice Flow,” International Journal of Fluid Power , vol. 3, no. 3, pp. 13-19, 2002.
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M. Annoni, L. Cristaldi, M. Norgia and C. Svelto, “Efficiency Measurement of Water Jet Orifices by a Novel Electrooptical Technique,” Journal of fluid mechanics, vol. 57, no. 1, pp. 48-54, 2007.
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R. D. C. D. T. C. R. A. R. M. C. H. A. W. L. W. S. C J Tegtmeyer, “Percutaneous transluminal dilatation of the renal arteries: techniques and results.,” Journal of Radiology, vol. 135, no. 3, 1980.
