Flow Through Orifice Meter

BY

PULKIT SHUKLA -2012UCE1291

SIDDHARTH KATIYAR

RAKESH KUMAR

Objective

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 .

Formulas Used

Discharge can be determined as follows:

Q=KH^n

K=(a1*a2* √2g)/ √((a1^2)-(a2^2)) m^3/sec

N=0.5(approximately)

Where, ,

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)

Continued……

H =h*((S1/S2)-1)

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”

Cd=Q(actual)/Q(theoretical)

Experimental Setup

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.

Procedure

Close the valves of inlet pipe, Orifice meter pipe line and manometer.

The gate valve of the pipeline selected for the experimentation is opened.

The needle valves of the corresponding manometer & Orifice meter are opened.

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.

Observation Table 1SNO.

AREA OF COLLECTING TANK(cm^2)

DEPTH OF

INITIAL(cm)

WATER

FINAL(cm)

COLLECTED

DIFFERENCE

VOLUME OF WATER COLLECTED(m3)

TIME(sec)

DISCHARGEQ(m3/sec)

1ST PIPE

1. 97*60 3 5 2 0.01164 30 0.000388

2. 97*60 5.5 7.6 2.1 0.01222 30 0.000407

3. 97*60 8.5 10.9 2.4 0.01396 30 0.000465

4. 97*60 11.5 15 3.5 0.02037 30 0.000679

5. 97*60 15.5 19.7 4.2 0.02444 30 0.000814

2ND PIPE

1. 97*60 23.7 25.3 1.6 0.009312 30 0.000310

2. 97*60 19 21.1 2.1 0.01222 30 0.000407

3. 97*60 21.2 25.4 4.2 0.02444 30 0.000814

4. 97*60 25.8 30.3 4.5 0.02619 30 0.000873

5. 97*60 29.7 34.6 4.9 0.028518 30 0.000950

Table 2S NO.

MANOMETERLIMB 1(cm)

READINGLIMB 2(cm)

READING DIFFERENCE(h) cm

H=h*12.6

DISCHARGE (Q) m3/sec

COEFFICIENT OF DISCHARGE

1ST PIPE

1. 18.5 8.5 10 126 0.000388 0.4075

2. 20 6.9 13.1 165.06 0.000407 0.373

3. 21 5.5 15.5 195.3 0.000465 0.394

4. 23.5 3.4 20.1 253.26 0.000679 0.5033

5. 24.2 2.8 21.4 269.64 0.000814 0.452

2ND PIPE

1. 13.3 12.8 0.5 6.3 0.000310 0.8516

2. 13.5 12.3 1.2 15.12 0.000407 0.722

3. 14.5 11.5 3.0 37.8 0.000814 0.913

4. 14.7 11.4 3.3 41.58 0.000873 0.933

5. 15.0 11.0 4.0 50.4 0.000950 0.842

CALCULATIONS

For 1st Pipe

d1=25mm d1=15 mm

Þ a1=490.873 mm^2 a2=176.82mm^2

By using Q(theoretical)=(a1*a2* Cd)/ √((a1^2)-(a2^2))

1.Q=0.000388,we get

Cd=(0.000388*457.72)/(490.73*176.82*5.0199*10^(-6))

Cd=0.4075

2.Q=0.00407

Cd=0.373

3.Q=0.000467 Cd=0.394

4.Q=0.000679 Cd=0.5033

5.Q=0.000814 Cd=0.584

Average Cd=0.452

For 2nd PIPE

d1=40mm d2=20mm

a1=1256.63mm^2 a2=314mm^2

1.Q=0.000310 Cd=0.8516

2.Q=0.000407 Cd=0.722

3.Q=0.000814 Cd=0.913

4.Q=0.000873 Cd=0.933

5.Q=0.000950 Cd=0.842

Average Cd=0.852

Graphs Q vs H

100 120 140 160 180 200 220 240 260 2800

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0.0009

0.000388 0.0004070.000465

0.000679

0.000814

1ST PIPE

HEAD(H)

Dis

charg

e (

Q)

Q vs H

0 10 20 30 40 50 600

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0.0009

0.001

0.00031

0.000407

0.0008140.000873

0.00095

2nd PIPE

HEAD(H)

DIS

CH

AR

GE(Q

)

Q vs H^(1/2)

10 11 12 13 14 15 16 170

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0.0009

0.000388 0.0004070.000465

0.000679

0.000814

1st PIPE

H^(1/2)

DIS

CH

AR

GE(Q

)

Q vs H^(1/2)

2 3 4 5 6 7 80

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0.0009

0.001

0.00031

0.000407

0.0008140.000873

0.00095

2nd PIPE

H^(1/2)

DIS

CH

AR

GE(Q

)

Log Q vs Log H

2.05 2.1 2.15 2.2 2.25 2.3 2.35 2.4 2.45

-3.5

-3.4

-3.3

-3.2

-3.1

-3

-2.9

-3.411-3.39

-3.332

-3.168

-3.089

1st PIPE

Log h

Log q

Log Q vs Log H

0.6 0.8 1 1.2 1.4 1.6 1.8

-3.6

-3.5

-3.4

-3.3

-3.2

-3.1

-3

-2.9

-2.8

-2.7

-3.508

-3.39

-3.089-3.058

-3.0222

2nd PIPE

LOG H

LO

G Q

Conclusion

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 relation.

Precaution

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.

Viva Voce

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 ?

Quiz

1) Venacontracta is at a distance of half the diameter of the orifice

a) True

b) False

2) The orifice diameter is 0.5 times the diameter of the pipe

a) True

b) False

3) The principle of orifice meter is different from that of the venturimeter

a) True

b) False