Venturi meter and orifice plate effects are two main and very important phenomenas in fuild mechanics sub field of mechanical engineering. In this post the effect of venturi meter and orifice plate on the fluid flow will be disciussed and complete work will be presented in the form of report.
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Aim and Objectives
Aim
The aim of this experiment is to study the overall meter coefficient C of Venture meter and Orifice plate
Objective
The objectives of this experiment are
1. Understand the effect of decrease in area on the velocity and pressure of the flowing fluid
2. Understand the relationship between velocity and pressure of flowing fluid
3. Find the meter coefficient for venture meter and orifice plate
Venture Meter
According to Michael ReaderHarris (n.d) Venture meter is an instrument use to study the flow of fluid when it passes through the converging section. There is an increase in the velocity and decrease in the pressure of the flowing fluid when the area available to flowing fluid decrease, this effect is called the venture effect named after the physicist who first introduces this theory.
Orifice Plate
According to Michael ReaderHarris (n.d) Orifice plate is an instrument use for three different applications one to measure the flow rate, second to restricting the flow and third is to reduce the pressure of the flowing fluid. It depends on the orifice plate associated calculation method that either mass flow rate or the volumetric flow rate is used for calculation. It uses the Bernoulli’s principle which shows the relationship between velocity and pressure of flowing fluid. When one increase then the second one decrease.
According to DANIEL MEASUREMENT and control white papers, following are the different types of orifice plates
The Thin Plate, Concentric Orifice
Eccentric Orifice Plates
Segmental Orifice Plates
Quadrant Edge Plate
Conic Edge Plate
Theory
According to Miller, R.W (1996) principle of continuity state that the decrease in the area of the flowing fluid will increase the velocity of the flowing fluid. With this increase in velocity of fluid, the fluid pressure will decrease to conserve the mechanical energy according to the law of conservation of energy.
Flow rate is the product of the velocity of the flowing fluid with area from which fluid is flowing. In venture meter the area of the tube decrease gradually due to which the velocity increase to keep the flow rate constant. In the orifice plate there is sudden decrease in the area of the flow due to restriction of the orifice plate. Due to this velocity will increase and pressure will decrease.
According to Bernoulli’s equation
P1+ 1/2×ρ×v1^2+ ρgh1=P2+ 1/2×ρ×v2^2+ ρgh2
As change in height is zero so
P1+ 1/2×ρ×v1^2= P2+ 1/2×ρ×v2^2
P2  P1= 1/2×ρ×〖(v〗1^2 v2^2)
As we know
Q=AV
Q=A √((2(P2P1)/ρ)/(〖[A1/A2]〗^21))
As we know
P= ρgh
So
Q= A1 √((2×g × ∆h)/(〖[A1/A2]〗^21))
In above equation
Q is flow rate
A1 is the area before convergence
A2 area of convergence (throat)
∆h is difference in height of heads across the convergence
For real fluid there will be difference in the theoretical and measured values this may be due to the meter coefficient C
Q= C ×A1 √((2×g × ∆h)/(〖[A1/A2]〗^21))
Apparatus
Orifice Tube and Venture Meter
Supply Hoses
Measuring Tank
Procedure
To setup the orifice tube and venture meter apparatus two tubes were connected one on each of the outlet and inlet of the apparatus. Tube which was connected to the venture meter outlet was further connected to the measuring tank. To level the orifice meter and venture tube apparatus, adjustable screws are provided at the apparatus.
Apparatus was connected to the power source to run the motor for water supply. Bench valve and the control valve of the apparatus were open to let the water move into the tube and to remove all the air pockets.
To raise the water level in the manometer tubes the control valve was closed gradually and when the height of water level was enough high then the bench valve was gradually closed. With both valves were closed there was a static water in the meter at a moderate pressure
Flow rate of the water was recorded and height of the water level was also recorded in all the tubes
Difference between the heights of water level and the flow rate will change upon opening any one of the apparatus valves. Flow rate was calculated by the noticing the time required to fill the tank of a known weight and at the same time the level of the water in the manometer tubes was also recorded
Same process are repeated for different flow rates
Sample Calculations
Mass = 6 Kg
Volume = 6/1000 =
0.006 cubic meter
Time = 12.81 sec
Flow Rate =
0.006/12.81 = 0.0004684 cubic meter/sec
For Venture
C = (0.0004684/0.053066)× 1/√((2×g × 0.267)/([26/16]^41))
C = 0.00943
Experimental Results
Table
1 Experimental Results
Results

Venture

Orifice


d1 = 26

d2 = 16

d1 = 51

d2 = 20


Test

Mass Kg

Time sec

Q m^3/sec

h1 mm

h2 mm

h1 mm

h2 mm

1

6

12.81

0.0004684

379

112

367

62

6

12.69

0.0004728

379

112

367

62


2

6

13.38

0.0004484

359

112

351

79

6

13.38

0.0004484

359

112

351

79


3

6

14.72

0.0004076

339

137

332

99

6

14.75

0.0004068

339

137

332

99


4

6

16.31

0.0003679

318

156

312

127

6

16.38

0.0003663

318

156

312

127


5

6

18.37

0.0003266

299

174

294

152

6

18.63

0.0003221

299

174

294

152


6

6

22.65

0.0002649

278

194

273

182

6

22.97

0.0002612

278

194

273

182

Table 2 Calculations
Calculations


Venture

Orifice


∆h m

C

∆h m

C

h1h2

h1h2


0.267

0.00943

0.305

0.006028

0.267

0.009519

0.305

0.006085

0.247

0.009386

0.272

0.006112

0.247

0.009386

0.272

0.006112

0.202

0.009434

0.233

0.006002

0.202

0.009415

0.233

0.00599

0.162

0.009508

0.185

0.006079

0.162

0.009467

0.185

0.006053

0.125

0.00961

0.142

0.006161

0.125

0.009476

0.142

0.006075

0.084

0.009508

0.091

0.006242

0.084

0.009376

0.091

0.006155

Discussion
· 1. Curve shown in the graphs shows the linear
relation between flow rate and difference in height
· 2. Result shows that with decrease in the flow rate
the value of the ∆h is also decreasing. So it can be said from the results that
the difference in the height of water level is directly proportional the flow
rate.
· 3. Change in the height of the water column of the
venture meter is much less than the change in the height of water column in the
orifice plate this is because the difference in diameter of the areas of
orifice is much more than the venture meter. So we can say that the difference
in height of water column is directly proportional to the difference in the
diameter of the area.
Conclusion
An experiment was conducted to
find the overall meter coefficient C in venture meter and orifice tube and
result show that the flow rate and ∆h are directly proportional to each other
and along with this ∆h and the ∆d are also directly proportional to each other.
Both these thing are important as they are used to calculate the overall meter
coefficient C
References
· 1. Michael ReaderHarris (n.d) Chapter 2 Orifice
plate, Orifice Plates and Venture Tubes, Spring
· 2. Miller, R.W (1996) Flow Measurement engineering
Handbook 3^{Rd} ED. McGrawHill Book, New York N.Y
3. USBR (1996) Flow Measurement Manual. Water
Resource Publication LLC Highland Ranch Co
4.Michael ReaderHarris (n.d) Chapter 3 Venture
tube, Orifice Plates and Venture Tubes, Spring
error analysis?
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