Calibration Of Rectangular Notch

Apparatus:

• Hydraulic bench
• Stopwatch
• Rectangular notch

Concepts:

NOTCH:

A Notch is regarded as an orifice with water level below its upper edge. Notch is made of a metallic plate and its use is to measure the discharge of liquids. These are used for measuring the flow of water from a vessel or tank with no pressure flow. Since the top edge of the notch above the liquid level serves no purpose therefore a notch may have only bottom edge and sides.

SILL “OR” CREST OF A NOTCH:

The bottom edge over which liquid flows is known as Sill or Crest of the notch.

RECTANGULAR NOTCH:

The notch which is Rectangular in shape is called as the rectangular notch. Coefficient of discharge (Cd): It is the ratio between the actual discharge and the theoretical discharge. Mathematically:

Procedure:

The stepwise procedure is given below:

1. Fix the plate having rectangular notch in the water passage of Hydraulic bench.
2. Turn the hydraulic bench on; water will accumulate in the channel.
3. When the water level reaches the Crest or sill of notch stop the inflow and note the reading, and design it as H1.
4. Restart the bench and note the volume and time of water that accumulates in the volumetric tank of bench, from this find the discharge, and also note the height of water at this point.
5. Find H = H2 – H1 This will give you the head over the notch.
6. Find the width of the notch.
7. Take different readings by changing the discharge head over the notch, using the above procedure.
8. Plot a graph between Log10H and Log10Q and find K from graph equation.

Find Cd from the following formula. Cd = 2 / 3 x k / √2g x b

b = 3 cm