Flow Through Orifice
PULKIT SHUKLA -2012UCE1291
To calibrate the given Orifice meter.
To draw graph between Q vs H, logQ vs logH, Q vs √H.
What‟s Orifice Meter?
ORIFICE METER is another simple device used for the measuring the
discharge through pipes, orifice meter also works on the same principle
as that of Venturi meter i.e., by reducing the cross-sectional area of
flow passage ,a pressure difference between the two sections before
and after Orifice is developed and the measurement of the pressure
difference enables the determination of the discharge through the
pipe . However , an orifice meter is a cheaper arrangement for
discharge measurement through pipes and its installation requires a
smaller length as compared with Venturi meter. As such where the
space is limited, the orifice meter may be used for the measurement of
discharge through pipes .
Discharge can be determined as follows:
K=(a1*a2* √2g)/ √((a1^2)-(a2^2)) m^3/sec
Qth= Theoretical dischargea
a1= c/s area of the inlet = c/s area of pipea
a2= c/s area of the throat
H = head (in meters of fluid flowing through the pipe)
h = differential manometer reading(difference in limb 1 and limb 2)
S1= Specific gravity of manometric liquid
S2= Specific gravity of fluid in the pipe.(i.e; water & S2= 1)
The actual flow rate is expected to be less than that given by the equation above
because of frictional effects and consequent head loss between section at inlet and
throat . In practice it is customery to account for this loss by insertion of an
experimentally determined co-efficient known as “Coefficient of Discharge”
The set up consists of a long horizontal pipe line. A thin plate having
a concentric sharp edged circular of diameter „d‟ is fitted in the
pipe line. Sufficient straight length is provided on the upstream of
the orifice plate.
A valve is fitted at the end of pipe to regulate the discharge Q. the
pressure tapings, one on the upstream side at (D-d) to 2 (D-d) and
the other on the downstream side at 0.5 area provided on the
horizontal pipe line. A u-tube mercury manometer is used to
measure the pressure difference between sections 1 and 2 . A stop
watch is also required to measure time.
Close the valves of inlet pipe, Orifice meter pipe line and
The gate valve of the pipeline selected for the experimentation is
The needle valves of the corresponding manometer & Orifice meter
Adjust the control valve kept at the exit side of the Orifice to a
desired flow rateand maintain the flow.
Note down the readings of manometer and final reading of
discharge tank for interval of 30 seconds.
Adjust the gate valve and repeat the experiment.
For 1st Pipe
By using Q(theoretical)=(a1*a2* Cd)/ √((a1^2)-(a2^2))
For 2nd PIPE
The largest contribution to the uncertainty in the measured
coefficient is due to the time measurement.
The main disadvantage of this meter is the greater frictional loss it
causes as compared with the other devices and hence causes
large power consumption.
Within the limits of the experimental uncertainty and the Reynolds
number range investigated, the results obtained for the discharge
coefficient through an orifice plate agree with the empirical
Drive out all entrapped air from differential mercury manometer.
Maintain a constant discharge before taking any reading.
Take a number of readings at lower value of Reynolds number, i.e.
at lower discharges.
What is the use of an orifice meter ? Compare the advantages and
disadvantages of and orifice meter and a venturimetre ?
How will you ascertain the direction of flow in an installed orifice meter
with its pressure connections projecting out. ?
Is there any factor to limit the minimum value of d/D that is workable ?
Why is the coefficient of discharge for orifice meter much less than that
of a venturimeter ?, Though both work on the same principle ?
It is required to keep a fairly long length of pipe free from
bends, valves, or any other obstruction inside before the orifice section
what is the idea ?
what is the influence of factor d/D on the value of Cd
Conclude the effects of viscosity on the value of Cd ?
1) Venacontracta is at a distance of half the diameter of the orifice
2) The orifice diameter is 0.5 times the diameter of the pipe
3) The principle of orifice meter is different from that of the