FLUID MECHANICS , EXPERIMENT # 4

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

APPARATUS:

•    Rectangular 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.

4. 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.

5. Jet:

The water issuing from an orifice is called jet.

6. Sill or Crest:

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

7. Nape or vein:

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

8. Rectangular Notch:

Let,

• H = Height of water above sill of notch

• b = Width or length of the notch

• C_d = Coefficient of discharge

Let us consider a horizontal strip of water of thickness dh at a depth of h from the water level as shown in figure.

•  Area of the strip 
• We know know that the theoretical velocity of water through the strip,
• Discharge through the strip,

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

PROCEDURE:

1. I fixed the plate having a rectangular 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 H₁.
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 width of notch. 
6. I took different readings by changing the discharge, head over the notch and tabulated flow.

PRECAUTIONS:

• Care should be taken at once stopped the inflow, when the water level reaches the crest of the notch.
• Different readings should be taken for different discharge.

OBSERVATION & CALCULATION:

S/no	Volume (lit)	Time (sec)	Q act		H1 (cm)	H2 (cm)	H (m)	Qth =2/3b* √2gH3/2	Cd =Qact /Qth
			Q (lit/s)	Q (m3/s)
1.
2.
3.
4.
5.
6.

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Posted in: Fluid Mechanics l