EXPERIMENTAL MANUAL
MODEL: FM 101
SOLUTION ENGINEERING SDN. BHD.
NO.3, JALAN TPK 2/4, TAMAN PERINDUSTRIAN KINRARA, 47100 PUCHONG, SELANGOR DARUL EHSAN, MALAYSIA. TEL: 603-80758000 FAX: 603-80755784 E-MAIL: [email protected]
FLOWMETER
MEASUREMENT
APPARATUS
FLOWMETER
MEASUREMENT
APPARATUS
Page
List of Figures... i
1.0 INTRODUCTION……….. .... 1
2.0 GENERAL DESCRIPTION 2.1 Sketch of apparatus and devices ... 2
2.2 Parts Identification ... 3 2.3 Specification of dimensions ... 4 2.4 General Requirements ... 4 3.0 SUMMARY OF THEORY 3.1 Rotameter ... 5 3.2 Venturi Meter ………...…... 5 3.3 Orifice Meter ... 7 3.4 90o elbow … ... 8 4.0 EXPERIMENTAL PROCEDURE 4.1 General Start-up Procedures ... 11
4.2 Demonstration of the operation and characteristic of three different basic types of flowmeter ... 13
4.3 Determination of the loss coefficient when fluid flows through a 90 degree elbow .... 14
4.4 General Shut-down Procedures ... 15
5.0 MAINTENANCE AND SAFETY PRECAUTIONS ... 16
6.0 REFERENCES... 17
APPENDIX A Experimental Data Sheet APPENDIX B Typical Experimental Results
Page
Figure 1 Sketch of apparatus and devices 2
Figure 2 Parts identification diagram 3
Figure 3 Specification of the venturi meter 4
Figure 4 Specification of the orifice plate 4
Figure 5 The rotameter 5
Figure 6 Venturi Meter 5
Figure 7 Orifice Meter 7
Figure 8 Piezometric head along a pipeline 8
1.0 INTRODUCTION
SOLTEQ® Flowmeter Measurement Apparatus (Model: FM101) apparatus is designed to operate together with a basic hydraulic bench or any water supply. It is to familiarize the students with typical methods of flow measurement of an incompressible fluid.
The apparatus is able to demonstrate the flow measurement comparison by using a venturi device, orifice device and rotameter. The flow comparison can be further be used to compare against the flow measurement of the hydraulics bench which can be either by Gravimeteric or Volumetric Method, depending on the type of hydraulics bench in use. Other features of the flow apparatus include a 90 degree elbow with pressure tappings before and after this elbow. The purpose of these features is to provide an added function to this apparatus to allow students to calculate the total head loss and loss coefficient when fluid flows through these devices.
In short, the apparatus allows following range of experiment to be carried out:
a) Direct comparison of flow measurement using venturi, orifice, rotameter and bench. b) Determination of total head loss and loss coefficient of fluid flow through a 90 degree
elbow.
2.0 GENERAL DESCRIPTION
2.1 Sketch of apparatus and devices
2.2 Part Identification
Figure 2: Part Identification Diagram
1. Manometer Tubes 6. Rotameter
2. Discharge Valve 7. 90° Elbow
3. Water Outlet 8. Orifice
4. Water Supply 9. Venturi
5. Staddle Valve 4 3 2 1 5 6 7 8 9
2.3 Specification of dimensions i) Venturi meter
Figure 3: Specification of the Venturi Meter
Tapping A = 26 mm Tapping B = 21.6 mm Tapping C = 16 mm Tapping D = 20 mm Tapping E = 22 mm Tapping F = 26 mm ii) Orifice
Figure 4: Specification of the Orifice Plate
Orifice upstream diameter (G) = φ26 mm Orifice diameter (H) = φ16 mm
2.4 General Requirements
SOLTEQ ® Hydraulic Bench (Model: FM110) C
A B D E F
3.0 SUMMARY OF THEORY 3.1 Rotameter
The rotameter is a flow meter in which a rotating free float is the indicating element. Basically, a rotameter consists of a transparent tapered vertical tube through which fluid flow upward. Within the tube is placed a freely suspended “float” of pump-bob shape. When there is no flow, the float rests on a stop at the bottom end. As flow commences, the float rises until upward and buoyancy forces on it are balanced by its weight. The float rises only a short distance if the rate of flow is small, and vice versa. The points of equilibrium can be noted as a function of flow rate. With a well-calibrated marked glass tube, the level of the float becomes a direct measure of flow rate.
Figure 5: The Rotameter
3.2 Venturi Meter
The venturi meter consists of a venturi tube and a suitable differential pressure gauge. The venturi tube has a converging portion, a throat and a diverging portion as shown in the figure below. The function of the converging portion is to increase the velocity of the fluid and lower its static pressure. A pressure difference between inlet and throat is thus developed, which pressure difference is correlated with the rate of discharge. The diverging cone serves to change the area of the stream back to the entrance area and convert velocity head into pressure head.
Figure 6: Venturi Meter
Tapered tube Flow Scale 1 2 Inlet Throat
Assume incompressible flow and no frictional losses, from Bernoulli’s Equation 2 2 2 2 1 2 1 1 2 2 g Z v p Z g v p + + = + +
γ
γ
……….………...(1)Use of the continuity Equation Q = A1V1 = A2V2, equation (1) becomes
− = − + − 2 1 2 2 2 2 1 1 2 2 1 A A g V Z Z p p
γ
……….………...(2) Ideal 2 1 2 1 2 1 2 1 2 2 2 2 2 1 2 1 / / − + − − = = − Z Z p p g A A A V A Qγ
…………...…(3)However, in the case of real fluid flow, the flow rate will be expected to be less than that given by equation (2) because of frictional effects and consequent head loss between inlet and throat. In metering practice, this non-ideality is accounted by insertion of an experimentally determined coefficient, Cd that is termed as the coefficient of discharge. With Z1 = Z2 in this apparatus, equation (3) becomes
Actual 2 1 2 1 2 1 2 2 2 1 2 1 − − × × = −
γ
p p g A A A Cd Q ………..…. (4) Hence,(
)
[
]
12 2 1 2 1 2 / 2 1 g P Pρ
A At At Cd q − − × × = − ………....…. (5) Where, Cd = Coefficient of discharge (0.98) D2 = Throat diameter = 16 mm D1 = Inlet diameter = 26 mm At = Throat area = 2.011 x 10-4 m2 A = Inlet area = 5.309 x 10-4 m2 g = 9.81 m/s2 ρ = Density of water = 1000 kg/m3 P1 = Inlet pressure (Pa)3.3 Orifice Meter
The orifice for use as a metering device in a pipeline consists of a concentric square-edged circular hole in a thin plate, which is clamped between the flanges of the pipe as shown in the figure below.
Figure 7: Orifice Meter
Pressure connections for attaching separate pressure gauges are made at holes in the pipe walls on both side of the orifice plate. The downstream pressure tap is placed at the minimum pressure position, which is assumed to be at the vena contracta. The centre of the inlet pressure tap is located between one-half and two pipe diameters from the upstream side of the orifice plate, usually a distance of one pipe diameter is employed. Equation (4) for the venturi meter can also be applied to the orifice meter where
Actual 2 1 2 1 2 1 2 1 2 2 1 2 − − × × = −
γ
p p g A A A Cd Q ………. (6)The coefficient of discharge, Cd in the case of the orifice meter will be different from that for the case of a venturi meter.
(
)
[
]
12 8 7 2 1 2 2 1 g h h A At At Cd Q − − × × = − ……….(7) Where, Cd = Coefficient of discharge (0.63) D7 = Orifice diameter = 16 mmD8 = Orifice upstream diameter = 26 mm At = Orifice area = 2.011 x 10-4 m2
A = Orifice upstream area = 5.309 x 10-4 m2 (h7 – h8) = Pressure difference across orifice (m)
A1
3.4 90o elbow
Figure below shows fluid flowing in a pipeline where there is some pipe fitting such as bend or valve, and change in pipe diameter. Included in the figure is the variation of piezometric head along the pipe run, as would be shown by numerous pressure tappings at the pipe wall.
Figure 8: Piezometric head along a pipeline
If the upstream and downstream lines of linear friction gradient are extrapolated to the plane of fitting, a loss of piezometric head, ∆ h, due to the fitting is found. By introducing the velocity heads in the upstream and downstream runs of pipe, total head loss, ∆H can be determined in which
g V g V h H 2 2 2 2 2 1 − + ∆ = ∆ ………(8)
Energy losses are proportional to the velocity head of the fluid as it flows around an elbow, through an enlargement or contraction of the flow section, or through a valve. Experimental values for energy losses are usually expressed in terms of a dimensionless loss coefficient K, where
g V H or g V H K 2 2 22 2 1 / / ∆ ∆ = ………..………(9)
depending on the context.
V22 / 2g V12 / 2g H h V 2 V 1
For results of better accuracy, long sections of straight pipe are required to establish with certainty the relative positions of the linear sections of the piezometric lines. However, in a compact apparatus as described in this manual, only two piezometers are used, one placed upstream and the other downstream of the fitting, at sufficient distances as to avoid severe disturbances. These piezometers measure the piezometric head loss, ∆ h’ between the tapping. Thus
f h h h=∆ −∆ ∆ ' ………..………(10) Where = ∆ g V D L f hf 2 4 2
Δhf = friction head loss which would be incurred in fully developed flow along the run of pipe between the piezometer tappings
f = friction factor
L = distance between the piezometer, measured along the pipe center line D = pipe diameter
V = average velocity of fluid flow in pipe
The friction head loss is estimated by choosing a suitable value of friction factor, f for fully developed flow along a smooth pipe. The method used in this manual to determine the friction factor is the prandtl equation
(
)
044
1 = logRe f − .
f ………(11)
Typical values derived from this equation are tabulated in the table below:
Re, x 104 0.5 1.0 1.5 2.0 2.5 3.0 3.5
F, x 10-3 9.27 7.73 6.96 6.48 6.14 5.88 5.67
In determination of the fraction factor, f, it is sufficient to establish the value of f at just one typical flow rate, as about the middle of the range of measurement due to the fact that f varies only slowly with Re, and the friction loss is generally fairly small in relation to the measured value of ∆h’.
Characteristic of flow through elbow and at changes in diameter 90o Elbow
Figure below shows flow round a 90o elbow which has a constant circular cross section.
Figure 9: 90o Elbow
The value of loss coefficient K is dependent on the ratio of the bend radius, R to the pipe inside diameter D. As this ratio increase, the value of K will fall and vice versa. g V K H = × 2/2 ………..………(12) Where, K = Coefficient of losses V = Velocity of flow g = 9.81 m/s2 D V R
4.0 EXPERIMENTAL PROCEDURES 4.1 General Start-up Procedures
The Flowmeter Measurement Apparatus (Model: FM 101) is supplied ready for use and only requires connection to the Hydraulic Bench (Model: FM 110) as follows: a) Place the apparatus on top of a suitable hydraulic bench.
b) Level the apparatus on the bench top.
c) Connect the hydraulic coupling to the outlet supply of the hydraulic bench. d) Connect the discharge connect of the flow apparatus hose to the collection
tank of the hydraulic bench.
e) You are now ready to start the apparatus.
Starting up the Apparatus:
1. Fully close the flow control valve of hydraulic bench and fully open the discharge valve.
2. Ensure that discharge hose is properly directed to volumetric tank of fibreglass before starting up system. Also ensure that volumetric tank drain valve is left OPEN to allow flow discharge back into sump tank. 3. Once step (b) is confirmed start up the pump supply from hydraulic bench.
Open the bench valve slowly. At this point, you will see water flowing from hydraulic bench through to the flow apparatus and discharge through into the volumetric tank of hydraulic bench and then drained back into sump tank of hydraulic bench.
4. Proceed to fully open the flow control valve. When the flow in the pipe is steady and there is no trapped bubble, start to close the bench valve to reduce the flow to the maximum measurable flow rate.
5. You will see that water level in the manometer board will begin to display different level of water heights. (If the water level in the manometer board is too high where it is out of visible point, adjust the water level by using the staddle valve. With the maximum measurable flow rate, retain maximum readings on manometer).
6. At this point, slowly reduce the flow by controlling the flow discharge valve of apparatus; you may close this discharge valve totally.
7. You will begin to see that the water level in the manometer board will begin to level into a straight level. This level maybe at the lower or maybe at the higher end of the manometer board range. (Take note that the pump from the hydraulic bench is at this time, still supplying water at a certain pressure in the system).
8. Also be on the lookout for “Trapped Bubbles” in the glass tube or plastic transfer tube. You would want to remove them from the system for better accuracy. To do this, you can either slowly “press the plastic tube to push the bubbles up or lightly “tab” the glass tube to release the bubbles upwards.
Note:
If above methods fail, then you will now have to “flush” the system by “bleeding” to air out.
All that is required is the use of a small object such as pen or screw driver, to depress the staddle valve, found at the top right side of manometer board.
Depress staddle valve lightly to allow fluid and trapped air to escape out. (Take care or you will wet yourself or the premise).
Allow sufficient time for bleeding until all bubbles escape.
Once all bubbles have been “bleed”, start to reduce the water supply now by manipulating BOTH control valves, reducing first the flow apparatus discharge valve and then the hydraulic bench valve in alternate motion, bringing down the DATUM level of the water in the manometer board.
(i) At this point you may start the experiment proper.
(j) You are ONLY interested in the data obtained from tubes: Probe A and C for venturi calculation
Probe G and H for orifice calculation
Probe I and J for 90 degree elbow calculation
All other probe readings are for viewing of pressure curve ONLY.
(k) With above guide, record water level of each probe at a certain flow. With the height difference (∆h), use formula provided to calculate. Verify the results obtained against rotameter and hydraulic bench for experiment of flow measurement comparison.
4.2 Demonstration of the operation and characteristic of three different basic types of flowmeter
Objective:
To obtain the flow rate measurement by utilizing three basic types of flow measuring techniques; rotameter, venturi meter and orifice meter. Procedures:
1. Place apparatus on bench, connect inlet pipe to bench supply and outlet pipe into volumetric tank.
2. With the bench valve fully closed and the discharge valve fully opened, start up the pump supply from hydraulic bench.
3. Slowly open the bench valve until it is fully opened.
4. When the flow in the pipe is steady and there is no trapped bubble, start to close the bench valve to reduce the flow to the maximum measurable flow rate. 5. By using the air bleed screw, adjust water level in the manometer board.
Retain maximum readings on manometers with the maximum measurable flow rate.
6. Note readings on manometers (A - J), rotameter and measured flow rate. 7. Step 6 is repeated for different flow rates. The flow rates can be adjusted by
utilizing both bench valve and discharge valve.
8. To demonstrate similar flow rates at different system static pressures, adjust bench and flow control valve together. Adjusting manometer levels as required.
4.3 Determination of the loss coefficient when fluid flows through a 90 degree elbow
Objective:
To investigate the loss coefficient of fluid through 90 degree elbow. Procedures:
1. Place apparatus on bench, connect inlet pipe to bench supply and outlet pipe into volumetric tank.
2. With the bench valve fully closed and the discharge valve fully opened, start up the pump supply from hydraulic bench.
3. Slowly open the bench valve until it is fully opened.
4. When the flow in the pipe is steady and there is no trapped bubble, start to close the bench valve to reduce the flow to the maximum measurable flow rate. 5. By using the air bleed screw, adjust the water level in the manometer board.
Retain maximum readings on manometers with the maximum measurable flow rate.
6. Note readings on manometers (I and J) and measured flow rate.
7. Step 6 is repeated for different flow rates. The flow rates can be adjusted by utilizing both bench valve and discharge valve.
8. Complete the tables below. 9. Plot graph ∆H against
g Vs
2 2
for 90 degree elbow to determine the coefficient of losses.
4.4 General Shut-down Procedures
1. Close water supply valve and venturi discharge valve. 2. Turn off the water supply pump.
5.0 MAINTENANCE AND SAFETY PRECAUTIONS
1. It is important to drain all water from the apparatus when not in use. The apparatus should be stored properly to prevent damage.
2. Any manometer tube, which does not fill with water or slow fill, indicates that tapping or connection of the manometer is blocked. To remove the obstacle, disconnect the flexible connection tube and blow through.
3. The apparatus should not be exposed to any shock and stresses.
4. Always wear protective clothing, shoes, helmet and goggles throughout the laboratory session.
6.0 REFERENCES
Applied Fluid Mechanics 5th Edition, Robert L. Mott, Prentice-Hall
Elementary Fluid Mechanics 7th Edition, Robert L. Street, Gary Z. Watters, John K. Vennard, John Wiley & Sons Inc.
Fluid Mechanics 4th Edition, Reynold C. Binder
Appendix A Experimental Data Sheets
Manometer reading (mm) Rotameter (l/min) Vol (l) Time (min) Flowrate, Q (l/min)
Flowrate calculated using the Bernoulli's Equation
(l/min)
Volume (L) Time (sec) Flowrate,Q (l/min)
Differential Piezometer Head, ∆h' (mm)
V V2/2g (m/s) (mm) Elbow (hI-hJ)
Appendix B
Manometer reading (mm) Rotameter (l/min) Vol (l) Time (min) Flowrate, Q (l/min)
Flowrate calculated using the Bernoulli's Equation
(l/min) A B C D E F G H I J Venturi Orifice 324 309 305 304 306 309 317 279 290 289 7 3 0.41 7.35 7.80 7.09 334 329 303 319 323 325 329 265 290 288 10 3 0.28 10.86 9.96 9.20 358 347 295 326 336 380 345 190 250 243 15 3 0.19 15.72 14.20 14.32 418 394 294 356 374 400 390 110 219 210 20 3 0.15 20.13 19.93 19.25 436 415 288 370 390 410 410 65 198 186 22 3 0.13 22.73 21.77 21.37
For rotameter flow rate = 22 l/min Venturi flow rate,
(
)
[
]
12 2 1 2 1 2 1 g hA hC A At At Cd q − − × × = −(
)
(
)
[
(
)(
)
]
m s q 29.81 0.436 0.288 / 10 309 . 5 10 011 . 2 1 10 011 . 2 98 . 0 12 3 2 1 2 4 4 4 − × × − × = − − − −(
)
(
)
[
(
)(
)
]
min 60 1 1000 288 . 0 436 . 0 81 . 9 2 10 309 . 5 10 011 . 2 1 10 011 . 2 98 . 0 12 2 1 2 4 4 4 l q − × × × − × = − − − − min / 77 . 21 l q=Orifice flow rate,
(
)
[
]
12 2 1 2 7 2 1 g hG hH A At At Cd Q − − × × = −(
)
(
)
[
(
)(
)
]
m s Q 29.81 0.410 0.065 / 10 309 . 5 10 011 . 2 1 10 011 . 2 63 . 0 12 3 2 1 2 4 4 4 − × × − × = − − − −(
)
(
)
[
(
)(
)
]
min 60 1 1000 065 . 0 410 . 0 81 . 9 2 10 309 . 5 10 011 . 2 1 10 011 . 2 63 . 0 12 2 1 2 4 4 4 l Q − × × × − × = − − − − min / 37 . 21 l Q=g v H K 2 / 2 ∆ = Slope = K=0.370 Volume (L) Time (min) Flowrate,Q (l/min)
Differential Piezometer Head, ∆h' (mm) V V2/2g (m/s) (mm) Elbow (hI-hJ) 3 0.55 5.43 1 0.17 1.48 3 0.30 10.07 2 0.32 5.09 3 0.23 13.29 3 0.42 8.88 3 0.16 18.42 6 0.58 17.05 3 0.13 22.87 10 0.72 26.27
Choose the min flow rate, Q = 5.43l/min = 9.05 X 10 m3/s
Velocity of flow in the pipe (Diameter = 26 mm)
