Calibration of V-Notch Experiment

Hello Friends. This is Mukesh from Learning Technology. I will tell you in today’s post How To perform Calibration of V-Notch Weir Experiment in a lab and How to find Co-efficient of Discharge in a very easy way.

Object of the Experiment

 a. To Calibration a V – Notch weir.

b. To determine the co-efficient of discharge (C_d).

Apparatus Required

 (a) Open channel tank fitted with V – Notch weir set up

(b) Volumetric measuring tank (30 cm x 30 cm)

(c) Stopwatch

Theory

 Weirs are a secondary instrument to measure the rate of discharge in an open channel flow. Triangular weir which is often called V – Notch is used when the discharge is relatively small. The basic formula for the rate of discharge is

Q_th = (8/15) √2g tanθ/2 x H^5/2

where, C_d = Co-efficient of discharge

θ = angle of V – Notch (45 degrees)

H = head of water over the V – Notch weir

The calibration of a triangular weir means establishing the relationship between C_d – H. The relationship is shown in a graphical form.

For a particular weir, θ is constant and C_d is taken constant. The ratio of discharge through the weir can be approximated by Q = KH^5/2 and K is usually called the meter constant.

Procedure

 Water is allowed to flow through the set-up by opening the flow control valve. Note the height of the water level in the volumetric tank. Divert the discharge from the weir into the volumetric tank and start the Stopwatch simultaneously. Note the glass gauge reading in the volumetric tank. Collect the water for some time and divert the discharge to the drain from the volumetric tank and at the same time stop the stopwatch.

Note the final water in the volumetric tank. We record time from the Stopwatch. Repeat the procedure three times at different discharges by opening the control valve.

Now, plot C_d – H ordinary graph paper (This curve is shown as calibration curve of the triangular weir)

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Practical Application

A triangular weir is used for the measurement of small discharges passing through an open channel. If over the weir is measured the discharge can directly obtainable from the calibration curve.

Observation

Area of the volumetric tank (A) in meter square = ……….

The angle of V – Notch (θ) = ……….

Results