EXPERIMENT :- CIRCULAR ORIFICE (constant head method )
AIM :- To determine the co-efficient of discharge (Cd) by constant head method
APPARATUS :- 01) Orifice Apparatus
02) Measuring Cylinder
03) Stop watch
co-efficient of discharge though an orifice is given by
Q = Cd. a. √2g . H1/2
Q = Discharge though the orifice
g = Acceleration due to gravity
Cd = Actual Discharge / Theoretical Discharge
Theoretical Discharge QT = a. √2g . H1/2
H = Water head
Writing the same equation in lo from to linearise
Log Q = ½ log10 H + log10 [Cd. a(√2g)]
Y = m X + C
By plotting Log10 QA Vs Log10 H , the value of Cd can be obtained for the intercept
01) Close the orifice of the middle wall of the apparatus by a plug. So that only the tank with
orifice plate is ready for experiment
02) Close the orifice with a plug and close the drain pipe with a clip.
03) Admit water in to the tank until a considerable head is built up.
04) Now open the orifice and obtain a constant head by adjusting the inflow Valve. (such
that, inflow = outflow).
05) obtain the time to collect some water in the cylinder and note the head, volume of water
collected and the time to collect the water.
06) Repeat the experiment 3 times with a certain head and repeat the process for about 6
In this experiment we had to use an orifice meter to determine the co-efficient of discharge by means of constant head method and the principle of Bernoulli’s was based for the experiment. In here we can learn the way how to find the co-efficient of discharge. Correctly using flow measurement apparatus hear we had measure the time (T) which is gone for the water level in to (h) value and was connected three times which followed average of these three values that we taken to calculate because, it can be error if we take the one measurement of the time
There can be the air bubbles with the water, so it can be another matter because the density of the water with the air bubbles is less than the density of the water with out air bubbles. There for at the beginning of this experiment the air bubble are allowed to remove
While we were doing this practical we can see some errors but we can get readings almost correct using above methods.
The equation is taken from beryllium equation for this experiment but the beryllium equation is correct only for the lamina flow of fluids. But the water floe through the orifice isn’t fully lamina flow, so that the value of co-efficient of discharge is not equal to actual co-efficient of discharge value. The height of the water level of the tank is increasing the speed of the flowing water is also increasing then the time which we get is reduced the percentage of error is also increasing.
We have to measure time and volume of the water in the same moment. That can be caused big mistake because we have to get the readings according to our naked eye’s
The errors which are mentioned above are done by us, we can minimize those errors then the accuracy of the experiment can be increased when the constant water volume is measured by using transparent utensil, then we can done the experiment almost correctly.
It is very important in the industrial to find Cd value for the fluids.
Ex:- Oil tank , industrial dryers , irrigation system
We have to find Cd value for the oil tank and irrigation system. Because it must know what is the value of the Cd then we can work easily. In above examples there are orifice meter, consist of flat orifice plate with circular hole drilled
So in industrial application, the Cd value is most important thing in dams the water inlet and outlet holes are also based on this theory.