EXPERIMENT 1- HD1

TITLE : FLOW THROUGH V NOTCH

OBJECTIVE : 1. To determine the discharge coefficient, Cd

2. To compare the experimental value of Cd with the value given by the manufacture.

THEORY : A variety of devices and methods are available for measuring fluid flow in the field and in the laboratory. One of these devices that can be used for flow measurement is weir.Essentially, a weir is a simple overflow structure extending across a channel and normal to the direction of flow. Various types of weirs exist, and they are generally classified by shape. In this experiment, a thin plate 90° V notch weir will be used for flow measurement. Before any measurement is made, the weir must be calibrated so that the discharge to be measured represents the actual discharge.

Theoretically, the flow through the V notch is given by

Q theory = 815

tan θ√2g H5/2 (1)

The actual discharge can be calculated by multiplying a coefficient (Cd) to theoretical discharge (eq.1) as follow

Q actual = Cd Q theory (2)

The value of Cd has to be calibrated in order for a notch to be used for flow measurement in open channel. The determination process of Cd is called calibration. Based on manufacture specification, Cd value for the apparatus is given as 0.61.

The theoretical discharge equation (eq.1) can be expressed as follows

Q = k Hn (3)

Or

Log Q = n log H + log k (4)

If experimental results are plotted on a graph having log H abcissae and log Q as ordinate, they will be on a straight line having slope n and intercept log k on the axis of log Q.

Theoretically, n value in equations (1) and (3) is equal 5/2. Therefore, the experimental n value should be about 5/2.

From the equations (1) and (3), the k term can be written as

K = 815

Cd √2g tan θ (5)

Therefore, the value of Cd can be determined from the equation (5) as follow

Cd = 158

k 1

√2 g tan θ (6)

Therefore, the value of k from the graph can be determine.

APPARATUS : V notch plate, hydraulic bench, stopwatch.

PROCEDURES :

1. The distance from the channel bed is measured to the apex of the notch, H0

2. The pump is switched on and the valve opened to give the maximum head over the notch.3. The volume of water collected is measured in the storage tank.4. The time to fill the water in the tank is recorded in step 2.5. The water surface elevation is measured above the channel bottom, H1

6. Step 4 and 5 is repeated for different discharge measurements.