UNIVERSITI TENAGA NASIONALCOLLEGE OF ENGINEERINGDEPARTMENT OF MECHANICAL ENGINEERING

MESB333ENGINEERING MEASUREMENT LABSEMESTER 1, 2014/2015

TITLE: DETERMINING FLUID VELOCITY AND DISCHARGE COEFFICIENT

AUTHOR: TUNKU ATIQAH BINTI TENGKU HAMNETSECTION: 3AGROUP: B

GROUP MEMBERS: FAIQAH BINTI MOHD FADZILME089856SOFEA BALQIS BINTI JUB,LIME090241RUCGNES A/L APPARAOME090233MOHAMAD AIMAN B. TALITME088598INSTRUCTOR:

DATE PERFORMED: 23 JUNE 2014DATE SUBMITTED: 30 JUNE 2014

TABLE OF CONTENT

EXPERIMENT I: DETERMINING FLUID VELOCITYSummary / Abstract3

Objective3

Theory3-5

Equipment6

Procedure6-7

Data, Observation and Results8-10

Analysis and Discussion10

Conclusion11

EXPERIMENT II: DETERMINATION OF DISCHARGE COEFFICIENTSummary / Abstract12

Objective12

Theory12-13

Equipment14

Procedure14

Data, Observation and Results15-18

Analysis and Discussion19

Conclusion20

SUMMARY/ABSTRACTSUMMARY/ABSTRACTIt is extensively used to verify the airspeed of an airplane, water speed of a boat, and to measure liquid, air and gas velocities in industrial applications. The pitot tube is used to evaluate the local velocity at a given position in the flow stream and not the average velocity in the pipe or conduit. The Bernoulli equation is then practical to calculate the velocity from the pressure difference. or (1)

When fluid flows through a immobile solid wall, the shear stress set up near to this boundary due to the relative motion between the fluid and the wall directs to the growth of a flow boundary layer. The boundary layer may be either laminar or turbulent in nature depending on the flow Reynolds number. The growth of this boundary layer can be discovered by examining the velocity profiles at selected cross-sections, the core region still outside the border layer showing up as an area of more or less consistent velocity. If velocity profiles for cross-sections different remoteness from the pipe opening are compared, the pace of growth of the boundary layer along the pipe length can be determined. Once the boundary layer has mature to the point where it fills the whole pipe cross-section this is termed "fully developed pipe flow".

OBJECTIVE1) To learn the method of measuring airflow velocity using pitot tube.2) To understand the working principle of pitot tube as well as the importance of Bernoulli equation in deriving and calculating the velocity.

THEORYA pitot tube is used to explore the developing boundary layer in the entry length of a pipe which has air drawn through it. With pitot tube, the velocity distribution profiles can be determined at a number of cross-sections at different locations along a pipe. With pitot tube, air flow velocities in the pipe can be obtained by first measuring the pressure difference of the moving air in the pipe at two points, where one of the points is at static velocity. The Bernoulli equation is then applied to calculate the velocity from the pressure difference. or (1)

p The pressure difference between the pitot tube and the wall pressure tapping measured using manometer bank provided (gx where x is the level of fluid used in the manometer). h the pressure difference expressed as a 'head' of the fluid being measured (air) The air density at the atmospheric pressure and temperture of that day.(kg/m3) g gravitational acceleration constant (9.81 m/s2) When fluid flows past a stationary solid wall, the shear stress set up close to this boundary due to the relative motion between the fluid and the wall leads to the development of a flow boundary layer. The boundary layer may be either laminar or turbulent in nature depending on the flow Reynolds number. The growth of this boundary layer can be revealed by studying the velocity profiles at selected cross-sections, the core region still outside the boundary layer showing up as an area of more or less uniform velocity. If velocity profiles for cross-sections different distances from the pipe entrance are compared, the rate of growth of the boundary layer along the pipe length can be determined. Once the boundary layer has grown to the point where it fills the whole pipe cross-section this is termed "fully developed pipe flow".

Reynolds NumberThe Reynolds number is a measure of the way in which a moving fluid encounters an obstacle. It's proportional to the fluid's density, the size of the obstacle, and the fluid's speed, and inversely proportional to the fluid's viscosity (viscosity is the measure of a fluid's "thickness"--for example, honey has a much larger viscosity than water does).

: fluid density v : fluid velocity d : obstacle size : coefficient of fluid dynamic viscosity

A small Reynolds number refers to a flow in which the fluid has a low density so that it responds easily to forces, encounters a small obstacle, moves slowly, or has a large viscosity to keep it organized. In such a situation, the fluid is able to get around the obstacle smoothly in what is known as "laminar flow." You can describe such laminar flow as dominated by the fluid's viscosity--it's tendency to move smoothly together as a cohesive material. A large Reynolds number refers to a flow in which the fluid has a large density so that it doesn't respond easily to forces, encounters a large obstacle, moves rapidly, or has too small a viscosity to keep it organized. In such a situation, the fluid can't get around the obstacle without breaking up into turbulent swirls and eddies. You can describe such turbulent flow as dominated by the fluid's inertia--the tendency of each portion of fluid to follow a path determined by its own momentum. The transition from laminar to turbulent flow, critcal flow, occurs at a particular range of Reynolds number (usually around 2500). Below this range, the flow is normally laminar; above it, the flow is normally turbulent.

Calculation of Airflow Velocity The manometer tube liquid levels must be used to calculate pressure differences, Dh and pressure heads in all these experiments. Starting with the basic equation of hydrostatics: p = gh (2) we can follow this procedure through using the following definitions: Example:

Manometer tubes1(static pressure*)2(stagnation pressure)

Liquid surface readings(mm)X1X2

Angle of inclination, =0

equivalent vertical separation of liquid levels in manometer tubes,h = (x1 - x2)cos(3)

If rk is the density of the kerosene in the manometer, the equivalent pressure difference p is:p = k gh = k g(x1 - x2) cos(4)

The value for kerosene is rk = 787 kg/m3 and g = 9.81 m/s2. If x1 and x2 are read in mm, then:p = 7.72(x1 - x2)cos [N/m2](5)

The p obtained is then used in second equation (1) to obtain the velocity.To use the first equation (1), convert this into a 'head' of air, h. Assuming a value of 1.2 kg/m3 for this gives: [N/m2](6)

APPARATUS

Figure 1: Experiment Apparatus

PROCEDUREa) Five mounting positions are provided for the pitot tube assembly. These are: 54 mm, 294 mm, 774 mm, 1574 mm and 2534 mm from the pipe inlet b) Ensure that the standard inlet nozzle is fitted for this experiment and that the orifice plate is removed from the pipe break line. c) Set the manometer such that the inclined position is at 00. d) Mount the pitot tube assembly at position 1 (at 54mm, nearest to the pipe inlet). Note that the connecting tube, the pressure tapping at the outer end of the assembly, is connected to a convenient manometer tube. Make sure that the tip, the L-shape metal tube of the pitot tube is facing the incoming flow. e) Note that there is a pipe wall static pressure tapping near to the position where the pitot tube assembly is placed. The static pressure tapping is connected to a manometer tube. f) Position the pitot tube with the traverse poisition of 0mm. Start the fan with the outlet throttle opened. g) Starting with the traverse position at 0mm, where the tip is touching the bottom of the pipe, read and record both manometer tube levels of the wall static and the pitot tube until the traveverse position touching the top of the pipe. h) Repeat the velocity traverse for the same air flow value at the next positon with the pitot tube assembly. Make sure that the blanking plugs is placed at the holes that are not in use.

DATA, OBSERVATION AND RESULTSData Sheet for Velocity Measurement Using Pitot TubeTraversePosition(mm)Pitot Tube at 54 mmStatic Pressure Reading117 mmPitot Tube at 294 mmStatic Pressure Reading120 mm

StagnationPressureReading(mm)x(mm)p(N/m2)Velocity(m/s)StagnationPressureReading(mm)x(mm)p(N/m2)Velocity(m/s)

010017131.2414.7910020154.416.05

109819146.6815.649921162.1216.45

209720154.416.059822169.8416.83

309621162.1216.459723177.5617.21

409522169.8416.839624185.2817.58

509522169.8416.839624185.2817.58

609522169.8416.8397.522.5173.717.02

709522169.8416.8310218138.9615.23

TraversePosition(mm)Pitot Tube at 774 mmStatic Pressure Reading126 mmPitot Tube at 1574 mmStatic Pressure Reading130 mm

StagnationPressureReading(mm)x(mm)p(N/m2)Velocity(m/s)StagnationPressureReading(mm)x(mm)p(N/m2)Velocity(m/s)

010224185.2817.5811614108.0813.43

1010422169.8416.8311416123.5214.36

209828216.1618.9911218138.9615.23

309729223.8819.3311020154.416.05

409630231.619.6610030231.619.66

509828216.1618.999931239.3219.98

6010026200.7218.299832247.6420.30

7010620154.416.0511020154.416.05

Pitot Tube at 2534 mm

Static Pressure Reading 136 mm

TraversePosition(mm)StagnationPressureReading(mm)x(mm)p(N/m2)Velocity(m/s)

012115115.813.89

1011224185.2817.58

2011026200.7218.29

3010828216.1618.99

4011026200.7218.29

5010630231.619.66

6010828216.1618.99

7011620154.416.05

Sample CalculationTaking :- Pitot tube = 54mmStatic pressure reading = 117mmAt transverse position = 0mStagnation pressure reading is 100mmx = static pressure, x1 - stagnation pressure, x2 = 117mm - 100mm = 17mmp = 7.72 (x) cos where = 0o, cos 0o = 1 = 7.72 (17mm) = 131.24 N/m2Velocity, V = = = 14.79 m/s

Graph 1: Velocity against Traverse Position

ANALYSIS AND DISCUSSION1. From the data collected, we have plotted the graph of velocity against transverse position. The velocity of the Pitot Tube can be expressed as sinusoidal position or look like the Simple Harmonic Motion (SHM) of its corresponding transverse position. Pitot tube of 2534 mm have the best symmetrical sinusoidal shape where as pitot tube of 54 mm have unsymmetrical sinusoidal shape.2. While conduction this experiment, there are lots of possible errors that has resulted in the inaccuracy of the results obtained. Among the sources of error is parallax error during the process of taking the value of manometer. The manometer level fluctuates at a very high and inconsistent rate making it hard to collect the accurate reading. This error can be said as the main source of error as the value of manometer that taken influences the results of the experiment.

CONCLUSIONThe objective of the experiment is achieved. The principle fluid (air) velocity measurement is explored and understood. The understanding on how to compute parameters such as x, p and the velocity with the help from the data obtained from the experiment is enhanced.

SUMMARY/ABSTRACTAn orifice plate meter shapes a precise and economical device for measuring the discharge for the flow of liquids or gases through a pipe. The orifice presented can be put into the suction pipe at the flanged joint about half way along its length. The multi-tube manometer given is used to determine the pressure fall across the orifice and this is associated to the discharge determined independently.

In this experiment, we are going to find out the discharge coefficient by conducting an experiment for an orifice plate in an airflow pipe. Also using the static pressure tapings given, we are determining the pressure distribution along the pipe downstream of the orifice plate. From the obtained CD of the orifice plate, we will determine the CD of a small nozzle.

OBJECTIVEThis experiment will ask student to determine the discharge coefficients, CD for orifice plate and the small nozzle.

THEORYThe orifice plate meter forms a jet, which expands to fill the whole pipe, some diameter distance downstream. The pressure difference between the two sides of the plate is related to the jet velocity, and therefore the discharge, by the energy equation: Q = Ajvj = AoCcvj = AoCcCvwhere,Q discharge (volume/time) _Aj jet cross-section area at minimun contraction (vena contracta) Ao orifice cross-2/4: d = orifice size) vj jet velocity at minimum contraction (vena contracta) Cc coefficient of contraction of jet Cv coefficient of velocity of jet g gravitational acceleration (9.81 ms -2) h pressure difference 'head' of air across orifice (refer to equation (6) of Exp. I)

These two coefficients are normally combined to give a single coefficient of discharge: CD = Cc.Cv Equation (1) now becomes Q = CDAO (2)

If Q can be determined independently, then the discharge coefficient can be determined as follows:- CD = (3)

Values of Qi can be determined if the standard nozzle is fitted at the pipe inlet. Qi = CDAii (4)

If hi = the drop in pressure head across the inlet, the discharge = (k/air )* (xbefore nozzle xafter nozzle): in which Ai = standard nozzle cross-section area (= pi*d2 /4) and CD assumed to be 0.97. Values of hI are obtained from the manometer tube levels connected to the pipe inlet pressure tapping and open to the atmosphere.

Calculating the CD of orifice plate: From equation (4), with the Qi obtained from standard nozzle where CD of standard nozzle is assumed to be 0.97, we can calculate the CD of orifice plate. Assuming that Qi across standard nozzle and Qo across orifice plate is the same, apply equation (3) CD = (5)where ho (k/air)*(x across orifice) Ao cross section area of orifice plate hole

APPARATUS

PROCEDURE(a) Insert the orifice plate in position (taking care to observe the instructions as to) in which the surface should face the approaching airflow. (b) Connect all the static pressure tapping points to the manometer tubes ensuring that one manometer tube remains unconnected to record room air pressure and that one is attached to the first tapping point adjacent to the standard inlet nozzle which should be fitted. (c) Turn on fan with low airflow (damper plate closed) and read all manometer tubes, including any open to the air (reading should be taken after the fan is on). (d) Gradually increase air flow by increasing the damper opening to 100%, and take read at all opening. Measure the diameter of the orifice plate, and the pipe for computing the cross sectional area and Reynolds number.

DATA, OBSERVATION AND RESULTSDamper Openings (% Openings)

0%25%50%75%100%

Pointsmm of kerosene

Room Pressure9694949494

After nozzle101103104105104

54 mm100104104105104

294 mm100104105106105

774 mm100106107109107

Before Orifice100107108110108

After Orifice113180200205208

1574 mm110160176182184

2534 mm107148160164165

Table 5.1 Static Pressure Readings when using Standard Nozzle (80 mm)

Damper Openings (% Openings)

0%25%50%75%100%

Pointsmm of kerosene

Room Pressure9592909089

After nozzle104130136138140

54 mm105132138140141

294 mm101116120121122

774 mm101118121122123

Before Orifice102119122124124

After Orifice114178193199202

1574 mm110164177181182

2534 mm108152163167168

Table 5.2 Static Pressure when using Small Nozzle (50 mm)

Damper Openings (% Opening)

Points0%25%50%75%100%

Qi0.0390.0530.0550.0580.055

Hi3.2795.9036.5587.2146.558

Cd0.5990.3440.3180.3300.305

Ho8.52647.8860.3462.3065.58

Re2659936147375113955737511

Table 2.3: Data of mm (kerosene) for each damper opening (diameter of orifice = 80mm)

Damper Openings (% Opening)

Points0%25%50%75%100%

Qi0.0200.0420.0460.0470.049

Hi5.90324.92230.16831.48033.448

Cd0.8200.7760.7750.7710.788

Ho7.8738.6946.5649.1951.16

Re3492473342803278207385565

Table 2.4: Data of mm (kerosene) for each damper opening (diameter of orifice = 50mm)

Sample CalculationTaking 0% damper openings with diameter 80mm:A0 = (3.142)(0.082) / 4 = 5.027 x 10-3 m2

ho = (Pk/Pair)(xafter orifice - xbefore orifice)/1000 = (787/1.2)(113-100)/1000 = 8.526 m h1 = (Pk/Pair)(xafter nozzle - xbefore nozzle)/1000 = (787/1.2)(101-96)/1000 = 3.279 m

CD = 0.97Qi = (Ai)(Cd)2ghi = (5.027 x 10-3)(0.97)(2)(9.81)(3.279) = 0.039 Reynold's Number, Re = ud/ = (1.2)(0.039/5.027 x 10-3)0.05 /1.75e-5) = 26599Cd = = = 0.5998

ANALYSIS AND DISCUSSION1. Based on the graphs plotted we can witness a sudden change in longitudinal pressure between 1000-1500 mm. This is expected because as the air flows, the orifice plate meter forms a jet that expands to fill up whole pipe, some diameter distance downstream. This will subsequently induce a significant pressure between the two sides of the plate. (Sudden increase in its longitudinal pressure or higher mm of kerosene).2. CD obtained in the orifice has smaller value in comparison with CD obtained for small nozzle. The two main contributors for the drag coefficient are the skin friction and form drag. These values are calculated by using the same mathematical formula and method. However the CD orifice is acquired by considering the difference of pressure before and after the orifice. Whereas, CD for small nozzle is obtained by taking into consideration the pressure difference between before and after the nozzle.3. The broader the damper opened, the higher the value of drag coefficient. The relationship between the opening damper and drag coefficient are directly proportional.4. Based on the graph plotted, as the damper opening increases from 0% to 100% , the longitudinal pressure at each points of the pipe will also generally decrease. The longitudinal pressure achieves maximum value at 208 mm Kerosene for standard nozzle and 202 mm for small nozzle when the damper opening is 100%. The pressure only reaches 113 mm Kerosene and 114 mm Kerosene for standard nozzle and small nozzle respectively when the damper opening is completely closed or at 0%. The data tells us that as the damper opening enlarge, the manometer readings and also increase. The damper opening provide outlet for air inside the pipe. As the opening become larger, more air can pass through it. Therefore, pressure at the finish of the pipe is reduced.5. The pressure in the pipe increases after the small opening of the orifice plate where the flow cross-section returns to its original value. The pressure downstream of the matter is lower that the upstream pressure because of the water resistance. The low pressure at the point of highest velocity creates the likelihood for the liquid to partially vaporize. It might remain partially vaporized after the sensor or return to a liquid state as the pressure increases after the lowest point

CONCLUSION In conclusions, since the objectives to determine the discharge coefficient, CD for orifice plate and the small nozzle is effectively done; this experiment can be considered as successful. Based on the data collected and the graph that we plot, we can wrap up that the pressure in the pipe increases after the small opening of the orifice plate where the flow crosses section return to its original value. Yet, because of the meter resistance, the pressure downstream of the meter is lower than the upstream pressure. The low pressure at the point of highest velocity builds the possibility for the liquid to partially vaporize and it might remain partially vaporized after the sensor or it may return to a liquid as the pressure increase after the lowest pressure point.As the damper opening increases from 0% to 100%, the longitudinal pressure at each points of the pipe will also reduce. In addition, this experiment enlighten the students understanding that as the damper opening enlarge from 0% to 50%, its corresponding CD is decreasing, before it rise up as the damper opening increase from 50% to 100%.

19

v = 2p

2gh'