Conversion, Calculations, and Analysis of Fluid Flow

The assignment content discusses the calculation of WC (294 Pa), conversion of % open diameter to % open area, and calculation of % flow rate for various devices such as orifice plate, nozzle, venturi meter, pitot tube, and iris valve. The results show that each device has its own unique characteristics and pressure drop profiles. Additionally, the content includes discussions on the merits and demerits of different flow measuring devices, as well as explanations on how to calculate the flow rate using the density of air.

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Measurement of Flow Characteristics of Meters and Valves
Introduction: Fluid flow is measured and controlled by obstructing the flow with suitable
devices or modification of the internal diameter profile. Five types of devices are studied in
this experiment. Orifice plate, with central hole in a blind flange; Nozzle, like orifice plate
but the hole extended by a short pipe segment; Venturi tube, with converging and diverging
bells; Pitot tube, involving adjustable radial position thin L-shaped tube and Iris valve, like
adjustable diameter orifice plate, are studied using controlled delivery air blower. The air
flow creates a pressure drop across the device. The flow rate and corresponding pressure drop
are measured and plotted for the various devices.
Aim: To study pressure drop characteristics of various air flow measuring and controlling
devices and verify theoretical equations.
Experimental Procedure:
1) The given device is bolted by flanges between two PVC pipe sections of 84.6mm NB.
2) The necessary pressure tapping points are connected to manometer(s) by rubber tubes.
3) The air blower is started and controlled at potentiometer settings of 2 to 8.
4) The air velocity is measured with anemometer.
5) The resulting pressure drop is measured as difference in water columns of manometer.
6) The water column pressure drop is converted to Pascal units and various plots are
made.
Results:
A) Nozzle
Characteristics
Potentiomete
r h (mm)
p
(N/m2)
sqrt(p)
(N0.5/m
)
Velocit
y (m/s)
2 4 39.2 6.3 1.4
3 8 78.5 8.9 2.1
4 15 147.2 12.1 2.8
5 23 225.6 15.0 3.5
6 33 323.7 18.0 4.2
7 46 451.3 21.2 5.0
8 63 618.0 24.9 6.0

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B) Orifice Plate Characteristics:
Potentiomet
er h (mm)
p
(N/m2)
sqrt(p)
(N0.5/
m)
Velocit
y (m/s)
2 4 39.2 6.3 1.2
3 9 88.3 9.4 1.9
4 16 157.0 12.5 2.5
5 23 225.6 15.0 3.1
6 35 343.4 18.5 3.8
7 48 470.9 21.7 4.4
8 64 627.8 25.1 5.1
C) Venturi Tube Characteristics:
Potentiomet
er
Measuri
ng Points h (mm)
p
(N/m2)
sqrt(p)
(N0.5/
m)
Velocit
y (m/s)
4 22 12 117.7 10.8 2.6
4 23 27 264.9 16.3 2.6
4 24 13 127.5 11.3 2.6
4 25 10 98.1 9.9 2.6
4 26 9 88.3 9.4 2.6
5 22 9 88.3 9.4 3.4
5 23 34 333.5 18.3 3.4
5 24 20 196.2 14.0 3.4
5 25 9 88.3 9.4 3.4
5 26 5 49.1 7.0 3.4
6 22 14 137.3 11.7 4.2
6 23 50 490.5 22.1 4.2
6 24 30 294.3 17.2 4.2
6 25 15 147.2 12.1 4.2
6 26 9 88.3 9.4 4.2
7 22 19 186.4 13.7 5.1
7 23 74 725.9 26.9 5.1
7 24 40 392.4 19.8 5.1
7 25 18 176.6 13.3 5.1
7 26 11 107.9 10.4 5.1
8 22 27 264.9 16.3 5.9
8 23 100 981.0 31.3 5.9
8 24 56 549.4 23.4 5.9
8 25 25 245.3 15.7 5.9
8 26 14 137.3 11.7 5.9

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D) Pitot Tube Study of Velocity Profile:
Potentiomet
er h (mm)
p
(N/m2)
sqrt(p)
(N0.5/
m)
Vertica
l
Distanc
e (mm)
Velocit
y x
Consta
nt
2 0 0.0 0.0 -40 0.0
2 1 9.8 3.1 -20 3.1
2 1 9.8 3.1 0 3.1
2 1 9.8 3.1 20 3.1
2 0 0.0 0.0 40 0.0
3 1 9.8 3.1 -40 3.1
3 3 29.4 5.4 -20 5.4
3 3 29.4 5.4 0 5.4
3 3 29.4 5.4 20 5.4
3 1 9.8 3.1 40 3.1
4 3 29.4 5.4 -40 5.4
4 7 68.7 8.3 -20 8.3
4 8 78.5 8.9 0 8.9
4 8 78.5 8.9 20 8.9
4 4 39.2 6.3 40 6.3
5 4 39.2 6.3 -40 6.3
5 10 98.1 9.9 -20 9.9
5 12 117.7 10.8 0 10.8
5 13 127.5 11.3 20 11.3
5 6 58.9 7.7 40 7.7
6 8 78.5 8.9 -40 8.9
6 19 186.4 13.7 -20 13.7
6 20 196.2 14.0 0 14.0
6 20 196.2 14.0 20 14.0
6 7 68.7 8.3 40 8.3
7 13 127.5 11.3 -40 11.3
7 28 274.7 16.6 -20 16.6
7 33 323.7 18.0 0 18.0
7 34 333.5 18.3 20 18.3
7 15 147.2 12.1 40 12.1

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E) Iris Diaphragm Valve Characteristics:
Potentiomet
er h (mm)
DP
(N/m2
)
sqrt(DP)
(N^0.5/m
)
Max
Velocit
y (m/s)
% Air
Flow
%Valve
Opening
Diamete
r
%
Valve
Openin
g Area
2 3 29.4 5.4 1.4 78.143 50.8 25.8
2 7 68.6 8.3 1.4
145.65
7 56.1 31.5
2 8 78.4 8.9 1.4
208.76
9 65.0 42.3
2 4 39.2 6.3 1.4
181.58
7 72.1 52.0
2 4 39.2 6.3 1.4
225.65
4 80.4 64.6
2 4 39.2 6.3 1.4
267.23
2 87.5 76.5
3 7 68.6 8.3 2.1 79.577 50.8 25.8
3 8 78.4 8.9 2.1
103.80
9 56.1 31.5
3 7 68.6 8.3 2.1
130.19
0 65.0 42.3
3 9 88.2 9.4 2.1
181.58
7 72.1 52.0
3 8 78.4 8.9 2.1
212.74
9 80.4 64.6
3 7 68.6 8.3 2.1
235.67
7 87.5 76.5
4 14 137.2 11.7 2.8 84.405 50.8 25.8
4 15 147.0 12.1 2.8
106.61
0 56.1 31.5
4 15 147.0 12.1 2.8
142.93
4 65.0 42.3
4 15 147.0 12.1 2.8
175.82
1 72.1 52.0
4 20 196.0 14.0 2.8
252.28
9 80.4 64.6
4 13 127.4 11.3 2.8
240.88
0 87.5 76.5
5 22 215.6 14.7 3.5 84.645 50.8 25.8
5 23 225.4 15.0 3.5
105.61
0 56.1 31.5
5 24 235.2 15.3 3.5
144.63
9 65.0 42.3
5 25 245.0 15.7 3.5
181.58
7 72.1 52.0
5 24 235.2 15.3 3.5
221.09
5 80.4 64.6

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5 20 196.0 14.0 3.5
239.02
0 87.5 76.5
6 33 323.4 18.0 4.2 86.391 50.8 25.8
6 34 333.2 18.3 4.2
107.00
4 56.1 31.5
6 35 343.0 18.5 4.2
145.55
7 65.0 42.3
6 38 372.4 19.3 4.2
186.56
3 72.1 52.0
6 36 352.8 18.8 4.2
225.65
4 80.4 64.6
6 30 294.0 17.1 4.2
243.94
8 87.5 76.5

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Sample Calculations:
1) Conversion of Water Column height to Pascal units:
30 mm WC = (30 m/1000) * (1000 kg/m3) * (9.8 m/s2) = 294 Pa
2) Conversion of % Open Diameter to % Open Area:
Let d be open diameter and D be the total diameter. Similarly, let a be open area and
A be the total area.
Now, a is proportional to d, giving
a/A = (d/D)2
This results in a/A*100 = (d/D*100)2/100
Therefore, %(open area) = (% open dia)2/100
3) Calculation of % Flow:
One can take iris valve open area as an orifice meter. The flow through the orifice is
given by the following equation (8.37 of McCabe and Smith, p. 219),
u0 = CD
√1−β4 ∗
√ 2∗gc∗( pa− pb )
ρ
Where, CD = 0.6 for orifice
β = d/D <= (.06)4 is nearly zero, as maximum open diameter is 0.06.
gc = 1 for SI units.
(pa – pb) = DP the manometer reading in Pascals.
ρ = 1.18 for air at 25C and 1 atmosphere pressure.
The actual flow is given by,
q= π
4 ∗d2∗u0
The maximum flow rate is given by,
Q= π
4 ∗D2∗V 0
The % flow rate is therefore,
q
Q∗100= ( % open area )∗u0
V 0
¿ ( % open area )∗(.6∗
√ 2∗DP
1.18 )/V 0
¿ ( %open area )∗( 0.781 )∗√ DP
V 0
For potentiometer setting of 6 and % open diameter = 6;
% (open area) = 0.36, √DP = 17.1 and V0 = 4.2 m/s.
Substituting in the above equation, % flow rate = 0.36*0.781*17.1/4.2 = 1.148.

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Graphs:
5.0 10.0 15.0 20.0 25.0 30.0
0
1
2
3
4
5
6
f(x) = 0.20332915291029 x
Orifice Plate Flow Characteristics
SQRT(DP in Pa)
Velocity in m/s
5.0 10.0 15.0 20.0 25.0 30.0
0
1
2
3
4
5
6
7
f(x) = 0.236183661084411 x
Nozzle Flow Characteristics
SQRT(DP in Pa)
Velocity in m/s

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2 2.5 3 3.5 4 4.5 5 5.5 6 6.5
0
5
10
15
20
25
30
35
Venturi Tube Flow Characteristics
22 23 24 25 26
Velocity in m/s
SQRT(DP in Pa)
Legends 22, 23, …, 26 are positions along the venture meter length.
Legends 2, 3, …, 7 are the potentiometer settings for the blower.
0 5 10 15 20
-50
-40
-30
-20
-10
0
10
20
30
40
50
Velocity
Radial
Distance in
mm
2
3
4
5
6
7

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20.00 30.00 40.00 50.00 60.00 70.00 80.00
0
50
100
150
200
250
300
Iris Valve Characteristics I
2 3 4 5 6
% Open Area
% Air Flow
Legends 2, 3, …, 6 are potentiometer settings for the blower.
20.0 30.0 40.0 50.0 60.0 70.0 80.0
0
50
100
150
200
250
300
f(x) = 3.40877128800865 x
Iris Valve Characteristics II
% Open Area
% Air Flow
The proportional constant of the valve is 3.34.
Discussion:
1) Orifice meter: The points lie in straight line and the constant correlating the Square
root of DP to Pipe Velocity is 0.2
2) Nozzle: The points lie in straight line and the constant of proportionality between Pipe
Velocity to Square root of DP is 0.24. The constant is higher than the one for orifice
plate as pressure drop is lower for the nozzle.
3) Venturi meter: The highest pressure drop occurs between the inlet pipe pressure and
the narrowest diameter of the venturi tube. The points for this legend number 23 and
the next one number 24 are almost in a straight line. Other points are almost in a
horizontal line.

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4) Pitot Tube: The velocity profile is almost flat in the central region, tapering to zero at
the pipe wall (+/- 42.3 mm). The velocity in the upper region of the centre appears to
be higher than the corresponding velocity in the lower region. This may be due to
position of the blower impeller with respect to the centre line of the discharge pipe.
5) Iris Valve: The % flow-rate is generally falling in a straight line with respect to %
open area. The constant of proportionality is on average 3.34 as shown in the diagram
without legends.
Conclusion: The theoretical equations are confirmed well for the devices studied in the
experiment. The deviations may be due to the error in measuring pressure drop and geometry
of blower.
Questions:
1) Merits of Orifice Plate, Nozzle, Venturi:
Orifice plate is least expensive, most compact but causes more irreversible and
reversible pressure drop.
Nozzle is more expensive, requires slightly more space and gives less pressure drops.
Venturi is the most expensive item, requires much larger space, gives high reversible
pressure drop and lower irreversible pressure drop.
2) Assuming density of air to be 1.18 kg/m3,
For nozzle, flow-rate = 1.1377*0.937*0.7854*0.25*sqrt(2*710/1.2) = 7.20 dm3/s
For orifice plate, flow-rate = 0.7588*0.9705*0.7854*0.25*sqrt(2*710/1.2)
= 4.97 dm3/s
3) Pitot tube has small diameter. To cause deflection of manometer sufficiently fast, the
manometer diameter should also be small.
4) Anemometer measures velocity of the air. (Wind and Weather tools, 2017).
5) Different pipe bends have different lengths and the angle of change in velocity
direction. The three-piece metre bend has gradual change in velocity direction, so it
gives the lowest pressure drop. The round elbow has shorter length but more sudden
turning of the direction giving more pressure drop. The two-piece metre bend has the
sharpest turn of air direction, so it gives the highest pressure drop.

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References
1) McCabe, W., J. Smith and P. Harriot (1993). Unit Operations of Chemical
Engineering, 5th edition, London: McGraw-Hill.
2) Wind and Weather Tools (2017). What is an Anemometer and What It is Used for,
https://windandweathertools.com/what-is-an-anemometer-and-what-is-it-used-for/
Accessed on 30th December 2017.