Laboratory Test No. 2Discharge Measurement Using Venturi Meter

Introduction:A Venturi meter is an instrument used for measuring the discharge through pipes. It consists of a

converging tube AB connected to the approach pipe at the inlet end A ending at the throat B. The diverging section BC connected to the pipe at the end C usually buillt as an integral part of the meter.

The pressure heads P1 / γ and P2 / γ are usually solved by attaching a differential manometers orat the inlet and throat.

The Venturi meter coefficient is best determined by measuring the actual flow Q through the meter by volume or by weight method, computing the theoritical flow Qt from the manometer readings and the meter dimensions, and finding the ratio of Q to Qt. The value of Cd is affected by the design of the meter and by the roughness of its inner surface. It has been found that the coefficient of a standard Venturi meter usually has a faitly constant value between 0.96 – 0.98, although for relatively small flowit drops to somewhat lower values.

Objectives:• To determine the coefficient of discharge Cd of a given Venturi meter.• To study the method of measuring the discharge of a flow system by means of Venturi meter.

Apparatus:1. Pipe assembly2. Venturi Meter3. Manometers4. Meter Stick5. Graduated Cylinder6. Stop Watch7. Balance

Theory: The discharge through a venturi meter is given by

Q = Ck √hwhere:

k = A1A2A1−A2

√2g

C is the discharge coefficient in cmsh is the head in meters

Procedure: 1. Measure the diameters of the inlet and the throat of the Venturi meter.2. Counnect the U-tube manometer to the Venturi meter.3. The supply valve is opened. Take the observations when the flow becomes steady.4. Collect a certain amount of water in a graduated cylinder. That time taken is determined with

the help of a stop watch. The volume of liquid is determined from the change in depth of liquid in the cylinder.

5. For that particular discharge, obtain the defection of the manometer attached to the Venturi meter.

6. The procedure is repeated for a different discharge which is obtained by regulating the supply valve. Perform atleast five trials. To get a good set of observations, the discharge is varied uniformly.

Observations:Diameter of inlet (d1), mm = 20.763 mmDiameter of throat (d2), mm = 10.3786 mmVolume of graduated container, mL = 900 mL

Results:

Trial No.ManometerDifference

(mm)

Volume(m³)

Time(s)

Discharge CoefficientOf

Discharge( Cd )

Qtm³/s

Qam³/s

1 23 9x10−4 19.16 4.697x10−5 2.39 0.99

2 21 9x10−4 18.91 4.759x10−5 2.29 0.99

3 17 9x10−4 20.66 4.356x10−5 2.06 0.99

4 18 9x10−4 20.63 4.363x10−5 2.12 0.99

5 19 9x10−4 21.4 4.206x10−5 2.18 0.99

Precautions1. The air bubbles in the manometer tubes cause errors. These bubbles should be removed.2. Fluctuations in the levels of mercury coulumn of the manometer cause difficulty. The readings

should be taken when the levels become stationary.3. Stop watch should be operated instantaneously as soon as the readings of the levels in the

measuring cylinder are taken.4. The readings of the liquid level in the graduated cylinder should be carefully taken.

Observation:The Fluid observed in the columns connected to the Venturi Nozzle flows upward or downward

observing the height being dependent on the increase in volume of fluid. In the series of columns, the one connected to a least area produced a low height of fluid. Also, the fluid attained a stable position when the upward force exerted by the fluid equals the gravitational force due to its weight.

Conclusion:Based on the data that we've gathered, we can say that our experiment is a success because

looking in to the coefficient of discharge, the data showed means that the volume if water that goes in is almost the same volume that comes out. Multiple results of static head and pressure head were obtained due to the columns attached to different cross- sections of the nozzle. The velocity can be calculated by using the Bernoulli Energy Equation, knowing that the velocity of fluid increases while the pressure decreases during the flow from a wider a wider to a narrower nozzle. Thus, the venturi meter is an effective apparatus in showing the principle of Bernoulli of incompressible fluids as it applies Bernoulli’s principle which is, an increase in velocity of a fluid will decrease the its pressure.

Photos of Actual Performance: