FLUID MECHANICS , EXPERIMENT # 5

To determine the discharge and co-efficient of discharge over a triangular notch

APPARATUS:

• Triangular Notch
• Hook and point gauge
• Hydraulic bench
• Stop watch

THEORY:

1. Notch:

An opening provided in the tank / vessel in which the top edge of the opening lies below the water surface.

2. Orifice:

An opening in the tank / vessel in which the top edge lies below the water surface level, both the orifice and notch are used directly for discharge.

3. Weir:

A structure, used to dam up a stream or river, over which the water flows, is called a weir.

Difference b/w Notch & Weir:

• Notch is of small size and weir is of a bigger one.
• Notch is usually made in plate, whereas a weir is usually made of masonry or concrete.

4. Jet:

The water issuing from an orifice is called jet.

5. Sill or Crest:

The top of the weir or notch over which the water flows, is known as Sill.

6. Nape or vein:

The sheet of water flowing through a notch/weir is called Nape/ vein.

7. Triangular Notch:

Let,

• H = Height of the liquid above the apex of the notch
• θ = Angle of the notch
• C_d = Coefficient of discharge

From the geometry of the figure, we find that the width of the notch at the water surface,

Area of the strip:

We know that the theoretical velocity of water through the strip

and discharge over the notch,

The total discharge over the whole notch may be found out only by integrating the above equation within the limits 0 and H.

•       A triangular notch gives more accurate results for low discharges than rectangular notch And the same triangular notch can measure a wide range of flows accurately.

   PROCEDURE:

    1. I fixed the plate having a      triangular notch in the water passage of hydraulic bench.

    2. .Then I turned the hydraulic bench “ON” and the water started accumulating in it & when the         water level reached the crest of the notch, stopped the inflow & noted the height, let it be H_1.

   3. Then started the inflow, Noted the value and time for its accumulation, this gave the               discharge. Also noted the height of water level for discharge, Let it be H₂.

   4. Then H₂-H₁ gives the head over the notch.

   5. Also noted the angle of notch

   6. I took different readings by changing the discharge, head over the notch and tabulated flow.

   PRECAUTION:

       1.The amount of water should be added very carefully.

       2. The stopwatch reading must come in zero after each reading.

      3. Different readings should be taken for different discharge.

S /no	Vol(lit)	Time       (sec)	Q act		H1         (cm)	H2        (cm)	H        (m)	Qth          =8/15√2g tan(Ф/2)H5/2	Cd       =Qact/Qth
			Q        (lit/s)	Q      (m3/s)
1.
2.
3.

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