FAKULTI TEKNOLOGI KEJURUTERAAN KEJURUTERAAN UNIVERSITI TEKNIKAL MALAYSIA MELAKA
FLUID MECHANICS
BETH 2313
SEMESTER 2
SESI 2017/2018
LAB 1: FLOW MEASUREMENT
NAME OF GROUP MEMBERS& MATRIX NUMBER
1. DEN ROKO BIN KASDI
B071610708
2. MUHD FIKRI BIN HASAN
B071610848 B071610848
3. NUN HAZIRAH BINTI BENJAMIN
B071610350
4. NUR INSYIRAH HANANI BINTI BI NTI MOHD LOK PI
B071610424
COURSE
2 BETR S2/1
DATE
14/2/2018
NAME OF INSTRUCTOR
1. SIR KHAIRIL AMRI BIN KAMARUZZAMAN 2.
EXAMINER’S COMMENT
VERIFICATION STAMP
TOTAL MARKS:
/ 100
LAB 1: FLOW MEASUREMENT
OBJECTIVES 1. To familiarize with the typical methods of measuring the discharge of an essentially incompressible fluid. The discharge is determined using a venturi meter, an orifice and a rotameter. 2. To investigate the relationship between the pressure head and velocity head along a venture, orifice and rotameter.
SCOPE The main purpose of this experiment is to understand and able to relate between all of the flow sensor which is orifice, venturi and rotameter. This experiment focuses on determine the flow rate of fluid down a pipe at different sections of the pipeline
INTRODUCTION The flow measuring apparatus was used to familiarize the students with typical methods of flow measurement of an incompressible fluid and, at the same time demonstrate applications of the Bernoulli’s equation. The flow is determined using a sudden enlargement, venturi meter, orific plate
and a Rotameter. The pressure drop associated with each meter is measured directly from the manometers. Water flow measuring apparatus is designed as a free-standing apparatus for use on the hydraulics bench, although it could be used in conjunction with a low pressure water supply controlled by a valve and a discharge to drain. Water enters the apparatus through the lower lefthand end and flows horizontally through a sudden enlargement into a transparent venturi meter, and into an orifice plate, a 90° elbow changes the flow direction to vertical and connects to a Rotameter, a second bend passes the flow into a discharge pipe which incorporates an atmospheric break.
Figure 1: Manometer basic flow
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The dark blue rectangle on the left is called as an element. It is like the rest of the flow in the bigger section, it flows with velocity v1. It is delimited left and right by faces with area A1. Note that, since the liquid left and right of it has pressure p1, this element is compressed by forces F1=p1A1 on each side. Now to the element on the smaller section, which flows faster. Its cross-sectional area is smaller. The pressure left and right of it is also smaller. As a result, the forces compressing it, F2=p2A2, are also smaller. So, p=F/A still holds. Yes, when the situation changes, A is smaller, which by itself would make p bigger. However, the new F is smaller than the old one too, which by itself would make p smaller. The net effect of p2
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PROCEDURES 1. The apparatus valve was opened until the rotameter showed a reading of approximately 10mm. When a steady flow maintained, the flow was measured with the Hydraulic Bench. The readings of the manometer were recorded in Table 1 during this period. 2. These procedures were repeated for number of equidistant values of rotameter readings.
RESULT Table 1 Test Number 1
2
3
4
A
340
330
320
304
282
B
330
316
298
262
222
C
334
328
316
310
274
D
338
330
318
300
272
E
338
328
318
288
274
F
330
314
290
250
200
G
330
316
296
258
212
H
330
316
294
258
210
I
230
212
190
154
108
Rotameter (cm)
0.1
0.3
0.5
0.7
0.9
Water (kg)
5
5
5
5
Time, T (second)
88
48
35.4
26.69
21.13
Venturi
3.042
3.599
4.152
6.234
7.452
Orifice
2.393
3.165
4.477
5.215
7.278
Venturi
3.593
0.855
1.088
0.570
0.798
Orifice
63.617
79.521
101.208
34.08
98.076
Diffuser
3.332
6.070
5.837
6.480
6.127
Elbow
7.815
5.049
6.934
0.483
1.395
Manometer Levels (mm)
Mass Flow Rate, m (kg/s)
5
5
Rotameter Weight Tank
AH/ Inlet Kinetic Head
Rotameter
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Figure 2: The movement of molecules
Figure 3: Area of Tube Affecting the Particles
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Calculation Formulas Mass Flow Rate, ṁ (kg/s)
Venturi Meter
(1)
ṁ= 0.962 x (hA – hB )1/2 kg/s
Orifice Meter
(2)
ṁ = 0.846 x (hE – hF) 1/2 kg/s
=
Head Loss
H Inlet Kinetic Head
Venturi Meter
Hac 2g
=
ha − hc
(3)
0.167 (ha − hb)
Orifice meter Head Loss =
0.0167(ℎ − hB ) 16
(4)
Orifice plate diameter approximately take the venturi inlet diameter, therefore the orifice inlet kinetic head is approximately 1/16 that of the venture. Thus, it i s divided by 16.
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Diffuser Head Loss =
2g
=
ℎ − ℎ + [ (0.167 (ℎ − ℎ ) −
0.167 (ℎ − ℎ ) 16
(5)
0.167(ℎ − ℎ )
Elbow Outlet kinetic head is now 2.8 times the inlet kinetic head. Inlet kinetic head =
0.167 (ℎ − ℎ )
(6)
16
Outlet kinetic head =
Head Loss =
0.167(ℎ − ℎ )
16
=
7
x 2.8
ℎ − ℎ + ( ℎ − ℎ) ℎ
7
(8)
DICSUSSION In this experiment, flow rate was measured by using orifice meter, venturi meter and the rotameter. They are compulsory to determine the pressure drop level that related to the velocity of fluid in the pipe based on Bernoulli principle. The results that have been obtained in table 1 showed the reading of every piezometer for five times with the manipulated value of the rotameter with increment of 20mm for each reading. Fixed variable has been set to be the outgoing stream of water, which is 5kg or 5 litre of it. Precisely, the time taken for the water to reach 5 litres also have been recorded. During the experiment, the relationship between the velocity of water and the cross-sectional area of the water flow has been observed. The velocity of water changed depending on the size of the area where the water flows. Based on Table 1, the reading of the piezometer keeps decreasing as the reading of rotameter increasing.
We observed that the velocity of water in the rotameter is
increasing while its pressure keeps decreasing as manometer I. The rotameter functions as a resistance in the flow of water. Based on venturi meter, the water level is drop at manometer b and f because the pressure in it decreases while velocity increases while flowing from one tube to another tube. The finding is consistent with the working principle of venture meter, which when fluid flows through the venturi meter, an increase in velocity and decrease in pressure occur. The rate of flow was measured at expense of this pressure difference. The speed of water determined by the position of rotameter. When the rotameter is at the lower position, the speed slower and vice versa. Speed of water affects the pressure on manometer at each position of the pipe. The table showed that all the manometer readings decrease as the flow rates of rotameter increases. The pipe has narrow diameter at certain area. As the rotameter position’s changed, the manometer level changed too. If the speed of water in the pipe is high, then the water level of manometer will be lower. This can be explained by referring back to Bernoulli’s
principle. From the data obtained, for the orifice meter high pressure drop unrecovered. This is due to the flow rate increased at the opening of the orifice plate and not much energy is lost but as it flows through and starts slowing down, much of the excess energy is lost.
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Velocity and Pressure were inversely proportional to the Area of cross section of the body through which a fluid flowed. Consider figure 2: An ideal fluid (that does not have viscosity (friction) among its molecules) flowed through the pipe. Consider the part AB of this pipe. The molecules leaving the pipe in 1 second equal to particle entering the pipe in 1 second. Assume 10 molecules can enter at a time through A at once and only 2 mo lecules can leave via B at a time. Let say 10 molecules enter the pipe per second that means 10 molecules must leave the pipe per second, but only 2 molecules can leave the pipe at once so to make this possible the pipe will have to eject 2 molecules in 0.2 seconds i.e. the molecules at A took 1 second to cover “x” distance and molecules at B took 0.2 seconds for the same condition. Thus, can be concluded that speed of particles at B faster than speed of particles at A. The area of cross section at A > area of cross section at B. Now, pressure changed at the moment it felt on the walls of a container due to molecules colliding at its walls per unit area (more collisions in a second per unit area more is the pressure felt). Now refer to figure 3, There is a wall bouncing between two walls at a constant speed and creates some pressure at point of collisions. If now one of the wall start to move towards the other, then the number of collisions of the ball and the wall per unit time increases and the pressure felt by the walls increases although the speed of the ball has not changed. Now back to Figure 2, same happened here as the molecules move towards B, the walls of the pipe gets closer and closer to each other and the particles collide more with the walls per second and the increment in pressure is observed. Errors are impossible to be avoided. This error can occur whenever there was some distance between the measuring scale and the indicator used to obtain a measurement. When taking readings, sometimes the positions of eyes are not parallel to the scale, thus errors occurred. The equipment used are also give factors to these error effect, such as the bubble in the tubes and manometers. Bubbles presence could disrupt the pressure existed in the tube thus gave inaccurate readings from the actual parameters that need to be measured. Bubbles can be eliminated by tapping the tubes over and over again repeatedly, and this should be done before doing the experiment. But after all, bubbles are allowed in certain cases, provided that the bubbles ’ size are not bigger tha t the tube’s diameter as well as their presence are not so abundant.
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CONCLUSION Then as for the rotameter, the energy losses were significantly higher than the venturi and orifice meters. This high energy loss is due to the large drop in pressure due to fr iction. For the venturi meter, the value obtained were closer to the actual flow rate this is due to lower pressure drop that results from its streamlined shape and almost eliminates boundary-layer separation and thus form drag is assumed negligible. It has a converging and a diverging part. Although, there may be some pressure loss in the converging part of the venturi meter but in a properly designed venturi meter. Some percentage of pressure loss is attained back in the diverging part of the meter. This meter is good for high pressure and energy recovery. To be concluded, venturi meter far more accurate compared to orifice meter and rotameter.
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REFERENCES 1. https://www.quora.com/What-is-the-relationship-between-velocity-pressure-and-area-in-fluiddynamics-If-area-increases-will-the-velocity-increase-or-decrease 2. https://physics.stackexchange.com/questions/95620/relation-between-pressure-velocity-and-area 3. http://www.coventry.ac.uk/research/areas-of-research/centre-for-flow-measurement-fluidmechanics/ 4. https://www.docsity.com/en/flow-measuring-devices-fluid-mechanics-lecture-notes/309109/ 5. https://quizlet.com/128164604/the-relationship-between-cross-sectional-area-and-velocity-ofblood-flow-flash-cards/
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