Gwh Feedback on Snortheim, Liu, Dufoe-Guiles, German

8/19/2019 Gwh Feedback on Snortheim, Liu, Dufoe-Guiles, German

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CEE410

Lab Assignment #2

Flow Measurement Testing

NOAH DUFOE‐GUILES

VANNA LIU

CRAIG SNORTHEIM

JACQUI GERMAN

November 26, 2014


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Introduction

Testing and calibration of flow meters is important for understanding the true volumetric flowrates in pipes so that a proper system analysis can be conducted. In this lab, we recordedreservoir tank elevation data and flow meter data at Unit Well 30 within the Madison WaterUtility district. Two types of flow meters were used: an acoustic (ultrasonic) flow meter, and amagnetic flow meter. The pump frequency was set to five different levels, and then turned backto full power while a control valve was progressively shut to three different levels. At each flowlevel, a steady flow rate was established by the pump operator, and flow and tank elevation datawas were recorded. With this data, we were able to compare the ‘true’ flow rate (change in tankvolume over time) to the readings on the flow meters. We averaged the measured flow rates thatfell into each interval, and assumed the ‘true’ flow rate was constant within a given interval. Inreality, the flow would change slightly was as the NPSH was changing over time. Our analysis

of the accuracy of the flow meters and the ensuing recommendations follows.

Literature Review

The selection of water and pressure sensors as well as flow meters is a detailed process.Environment Environmental conditions are considered (i.e. temperature, humidity, gases)however, adequate ventilation assists in minimizing the effect of many of these. Modern devicescan be useful in the sense they are generally more detail with up-to-date technology. Although,these unique instruments generally also require more highly skilled specialists for servicing andinstallation. Another important consideration that Bosserman et al. (2008) states is that,“Instrument systems usually consists of a number of interdependent elements, each of which

contributes to the total measurement of error, therefore errors are generally greater than the ones published in manufacturers literature,” (20.4). Pumping station instruments are selected to provide long lifespan, low maintenance, and high reliability in damp, corrosive environments.This selection process is specifically important to pumping stations as they are generallydesigned with a minimum lifespan of 20 years or more without major construction (Bosserman et

al., 2008). This literature review goes over pressure sensors, elevation sensors, and flow metersin the Unit Well 30 design as well as ones in the market.

Pressure Sensors

The pressure sensor or transducer also takes on the name pressure transmitter. This device

converts pressure into an analog electrical signal. This differs from discrete signals, whichreports a true/false signal (e.g. open/closed, running/stopped). These devices can be designed tofunction immersed in liquid and these are defined as submersible pressure transducers (Omega,2014).

Submersible pressure transducers have been around since the 1960s and are documented to beinvolved in the Unit Well 30 design (exact design is undetermined). They were developed torecord water level and pressure data. Combined with other pressure data collecting devices (e.g.

piezometers, tensiometers) these tools aid in providing continuous data. Differential pressuretransducers measure with respect to a varying pressure reference (e.g. ambient atmospheric

pressure). Freeman et al. (2004) evaluate evaluated the standard for USGS pressure transducer performance in terms of accuracy with error brackets (+/- 0.01 ft or 0.1 percent of expected

Commented [g1]: This is a good introduction but a sentence that starts with something like “the purp

this report is to …”

Commented [g2]: Try to use third person.

Commented [g3]: The word “data” is usually plur

Commented [g4]: This would actually be the totadynamic head because reservoir elevation in the sys

also changing. So, the discharge and suction elevati

both

changing

with

time.

Commented [g5]: I’m not sure what you are sayinbut I can guess. In my experience, the primary diffe

over time has been the ability of sensors to continuo

send electronic output to a supervisory control and

acquisition (SCADA) system.

Commented [g6]: “however” would be a better where.

Commented [g7]: Indeed, it is just as important founderstand the uncertainty in a set of measuremen

for us to understand the central tendency of those

measurements.

Commented [g8]: Simultaneously using “minimu“or more” is usually confusing to the reader.

Commented [g9]: Do we know how this device sepressure and then converts that to the analog signal

Commented [g10]: I’m not clear what this word ireferring to here. Is it referring to the device or to t

analog electrical signal?

Commented [g11]: Good – they perform both eleand pressure measurements.


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range) for most water level application. Omega (2014) recorded a high accuracy pressuretransducer in their inventory with an error percentage as low as 0.05% (stating the average

pressure transducer is around 0.25%).

There are a couple pressure transducers that areassumed not to be included in the Unit Well 30 system.The C-Shaped Motion-balance Bourdon-tube is utilizedfor measuring pressure (see figure 1; Freeman et al.,2004). As pressure increasing increases in the Bourdontube, the tube displaces a linear voltage differentialtransformer (LVDT). This system is generally not

preferred as it supplies a significant amount of wear onthe equipment and therefore decreases the incentives forusage (Bosserman et al., 2008). See Appendix C for amore detailed table of wastewater and clean waterapplication applications for pressure sensors.

Elevation sensors

Float sensors provide a means of measuring liquid elevation. These devices involve a buoyant body that remains at the liquid surface. Generally it is connected to a cable contraption thatallows free range in vertical direction, but restricts the range in the horizontal plane. This cableis then connected to a rod, possibly by means of a magnet, and as the system moves the magnet itactuates a switch returning feedback as to the level the liquid has reached.

Floaters are frequently used in wastewater applications however containbut have a few

disadvantages. Difficult to adjust, maintenance requiring access, and the wearing on the cable(2-3 years lifespan) are among the drawbacks. Due to likely debris in wastewater conditions

these devices are made larger than in the clean water industry and are generally not preferred.

Float switches are believed to be utilized at Unit Well 30 as stated in the design drawings. They provide a backup data feed to assist in calibration and data analysis. A very simplistic drawingof this device can be viewed in figure Figure 2. Specifically the example model’s performance(selected in figure Figure 2) is rated for is maximum current, frequency range, and the number ofmicro disconnect automatic life cycles (HCP Pump, 2011). These switches also aid in insuringthat the water level does not fill past a designated elevation or does not drain past a designated

elevation.

Figure 1: Diagram of a C ‐shaped Bourdon pressure

transducer (slightly modified from Freeman et al.,

2004)

Commented [g12]: Ok. Considering your earlier statement, it is probably higher than this in real‐wor

application. Also, manufacturers will sometimes co

apples with oranges to make their case. In this case

average might be in the field where their own data m

in well‐controlled laboratory conditions. Always con

manufacturer statements when you begin working a

engineer.

Commented [g13]: Ok, so what does the LVDT do

I see

how

this

device

works.

I’m

not

clear

how

the

p

device works.

Commented [g14]: On what equipment?

Commented [g15]: Nice summary.

Commented [g16]: This could be better written.

Commented [g17]: This is helpful.


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Figure 2: Diagram depiction of how a float switch operates (HCP Pump, 2011).

Floaters remain on the surface of the liquid while displacers remain below the surface. Displacerinstruments are selected to be denser than the liquid submersed in and are accompanied with aspring related system the displacer adjusts with the changing liquid level. Again the device isrestricted in its motion in the horizontal and allowing free range in the vertical. Theseinstruments are preferred in wastewater application due to their inherent washing as the devicecontinues to be used decreasing maintenance. See Appendix C for a more detailed table of

wastewater and clean water application.

Magnetic flow meter

Magnetic flow meters operate under the principle of Faraday’s Law of ElectromagneticInduction, which states that voltage generated in a conductor, E , is proportional to the velocity ofthe conductor, v, magnetic field strength, B, and length of conductor, D (equation 1, figure 3).

The conductor, in this case, is the liquid measured.

∝ ∗ ∗ (1)The magnetic flow meter induces a magnetic field onthe fluid of a known strength, and as the fluid movesthrough the magnetic field, a voltage signal isgenerated according to Faraday’s Law. Electrodeson the pipe walls sense this voltage and an electronictransmitter calculates the velocity of the moving fluid

(Instrumart, 2014).

There are several requirements with the use ofmagnetic flow meters in the fluid measured and

placement of the meter. The fluid has to be aconductive liquid, so conduits in de-ionized water,

hydrocarbon or gaseous service cannot be measured by a mag meter. In addition, the flow metermust be placed downstream of 3-5 diameters and upstream of 0-3 diameters straight run. Thisassures that the flow through the meter is laminar, assuring the most accurate measurements.

Figure 3. Operating principle of magnetic flow

meters (Universal Flow Monitors, 2014).

Commented [g18]: I’m not sure what this is refer

Commented [g19]: This is a nicely written section

Commented [g20]: Can mag meters be used in tuflow conditions? If yes, then “laminar” isn’t quite th

word.


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According to Bosserman et al. (2008), magnetic flow meters are one of the most accurate flowmeters available. The vendors typically report an accuracy of 0.5% of flow, but, “in situverification of calibration” (20.13) is critical, as with installation of any flow meters. In theexperiment conducted at Unit Well 30, this flow meter was used to measure the discharge of

Booster Pump #2.

Ultrasonic flow meter

Ultrasonic flow meters operate by the DopplerEffect, where frequency shifts of an ultrasonicsignal is are directly proportional to thevelocity of the fluid. Equation 2 explains thisrelationship, whereby f 1 is the frequencyinjected by the transducer, f a is the reflectedfrequency off bubbles or discontinuities in

flow, v is the velocity of ultrasonic wave in thefluid, and s is the velocity of the fluid(Bosserman et al., 2008). This relationship

can be seen pictorially with the figure Figure 4.

(2)

Similar to the magnetic flow meter, the advantage to the ultrasonic flow meter is that they arenonintrusive to conduit flow. An added benefit is that they can also be portable, as is the case in

the experiment conducted at Unit Well 30 (Smart Measurement, 2012). There is no probe thatneeds insertion, and no direct contact with the fluid is necessary for measurement.

With an error of up to 20%, ultrasonic flowmeters are not used in applications where accuracy iscritical. They are employed for wastewater service, as wastewater contains the “discontinuities”necessary for waves to reflect off of. Drinking water does not generally contain, “reliable

reflective surfaces” (Bosserman et al., 2008).

Venturi flow meter

Figure 5: Operating principle of venture flow meter (Fluid Mechanics, n.d.).

Conservation of energy and Bernoulli’s equation are the governing principles for venturi flowmeters. When a fluid travels from a larger cross-sectional area through a smaller area, pressure

Figure 4. Operating principle of ultrasonic flow meters (Smart

Measurement, 2012).

Commented [g21]: This was the primary purposelab report.

Commented [g22]: This figure could better explaEquation 2.

Commented [g23]: And why is this an advantage

Commented [g24]: Ok, I’m now curious how yourcompare.


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increases proportional to the change in area. The pressures are read from the pressure taps a andb in figure Figure 5. However, energy and flow at both points must remain the same. Usingequation Equation 3, which combines conservation of energy and Bernoulli’s equation, and

equation Equation 4, a mass balance, the flow can be solved for (Sleigh & Noakes, 2009).

∆

(3)

(4)In contrast to the two previously discussed flow meters, the venture venturi flow meter doesmaintain direct contact with the fluid. However, according to Bosserman et al. (2008), “headrecovery is excellent,” (20.14). That is to say the venturi flow meter does not disturb the flowsuch that it loses much energy. Because of the meter’s shape, it can actually correct anyirregularity in flow through the conduit/meter (Bosserman et al., 2008). This can be useful when

flow needs to measured where there is a very short straight run of pipe.

According to Engineering Toolbox (n.d.), the venturi flow meter can be accurate up to 10% offlow if calibrated properly. This kind of meter is generally used for drinking water applications,

as solids will disturb pressure measurements.

Methods

The pump was run at five different speeds as well as at full speed with the control valvemanually throttled at three different rates. Each of the pumping speeds were run long enough to

produce accurate results, approximately long enough to pump the reservoir down one foot. Timeand water elevation data were collected at the beginning and ending of the flow rate period. Once

the flowmeters stabilized multiple readings were collected from both the magnetic meter and theacoustic meter during each flow rate period. The flowmeter readings for each meter wereaveraged for each pumping speed.

The time and elevation changes were used to calculate volumetric flow rates for each pumpingspeed. This rate was then compared to the average rates recorded for each flowmeter throughoutthe same period and percent error was calculated. The results can be seen in Appendix B.

Conclusions and Recommendations

The results of our analysis show that the flow meters were generally within -5% to 15% of the‘true’ flow rates calculated via tank elevation changes over time. The magnetic meter was moreaccurate (between -4.6% and 10.8% error) than the acoustic flow meter (0.2% to +16.9%), as isexpected. The mean error of the magnetic meter was +0.2% while the mean error of the acousticmeter was +5.7%, suggesting that the acoustic meter was biased and tended to overestimate theflow. The acoustic meter likely showed greater error because it has a lower accuracy (0.5% and20% for the magnetic and acoustic meters, respectively), and because it was placed in close

proximity to a fitting which caused turbulence in the flow. The acoustic meter measurements fellwithin this accuracy range (+/- 20%), but the magnetic meter measurements did not (+/- 0.5%).

Commented [g25]: Be very careful using this worengineer because it puts you at risk for unanticipate

problems. There are insurance companies that call t

of

the

“forbidden

words”

in

legal

documents

such

asengineering reports.

Commented [g26]: Ok.

Commented [g27]: You didn’t use a venturi metelab but it would be calibrated with a similar approac

Commented [g28]: What does this refer to? Are saying long enough to produce an accurately measu

elevation change in the reservoir?

Commented [g29]: Always provide a written sumresults in a lab report’s main body.

Commented [g30]: In retrospect, I should have asto look up the acceptable error listed in state law (th

the section enforced by the Public Service Commissi

Commented [g31]: I’m missing something here –doesn’t seem consistent with the rest of the paragra


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This suggests that either the magnetic flow meter was not operating correctly, or the ‘true’ flow

rates are flawed.

We suggest that the reason for the relatively high error in the magnetic flow meter measurementsis due to sources of error in measuring the ‘true’ flow rates. The flow rates are based on changein elevation in the tank (digitally displayed to tenths of feet) over time (recorded to accuracy ofone minute). There is notable error associated with the timing of reading the tank elevationchanges (length of time since last change in digital display) and recording the time with a devicethat had only minute accuracy. Therefore, the ‘true’ flow rates have some considerable error

associated with them, and the error cannot be completely attributed to the flow meters.

Given the uncertainty in the baseline flow rate data (derived from tank volume), we are notmaking any recommendations related to the operational state of the flow meters. Instead, werecommend a more rigorous test be conducted with the following changes: 1) time recorded witha stopwatch or device with second resolution; 2) times recorded at exact time of the elevation

display changes; 3) longer time intervals at each flow. Alternatively, it might be helpful toutilize time-series elevation and flow data from the Utility if available. Finally, the portableacoustic flow meter should be placed as far from sources of turbulence (e.g. fittings, bends) as

possible.

Commented [g32]: This needs more explanation.

Commented [g33]: Perhaps we can get data fromSCADA system.

Commented [g34]: Ok.


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Bibliography

Bosserman, B. E, Jones, G. M, Sanks, R. L, & Tchobanoglous, G. (2008). Pumping stationdesign. Rev. 3rd ed. Amsterdam: Elsevier/Butterworth-Heinemann.

Fluid Mechanics (n.d.) “Applications of the Bernoulli Equation”http://www.efm.leeds.ac.uk/CIVE/CIVE1400/Section3/bernoulli-apps.htm Date Retrieved:

Novemeber 22, 2014

Freeman, L., Carpenter, M., Rosenberry, D., Rousseau, J., Unger, R., and McLean, J. (2004).Use of Submersible Pressure Transducers in Water-Resources Investigations Reston, Virginia;United States Geological Survey, Chapter A of Book 8, Instrumentation for Measurement ofWater Level.

HCP Pump (2011). “Float Switch” http://www.hcppump.com.tw/English/Archive/SJE.htmlDate Retrieved: November 22, 2014

Instrumart (2014). “Magnetic Flow Meters” https://www.instrumart.com/pages/223/magnetic-

flow-meters Date Retrieved: November 23, 2014

Omega (2014). “Pressure Transducers & Transmitters”http://www.omega.com/prodinfo/pressuretransducers.html Date Retrieved: November 22, 2014

Smart Measurement (2012). “Ultrasonic Measuring Principle”http://www.smartmeasurement.com/Products/FlowMeters/Ultrasonic/MeasuringPrinciple.aspxDate Retrieved: November 23, 2014

The Engineering Toobox (n.d.). “Types of Fluid Flow Meters”http://www.engineeringtoolbox.com/flow-meters-d_493.html Date Retrieved: November 23,2014

Universal Flow Monitors (2014). “Magnetic Flowmeter Technology”http://www.flowmeters.com/magnetic-technology Date Retrieve: November 22, 2014


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Appendix A

Raw Data


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Appendix B

Appendix C

Figure 6: Pressure Measuring Elements (Bosserman et al., 2008)

Figure 7:

Level

Measuring

Elements

(Bosserman

et

al.,

2008)

Time

Period

Elapsed

Time

(min)

Change

Elevation

(ft)

Change

Volume

(ft^3)

Change

Volume

(gal)

Flowrate

(gpm)

Mag

Meter

(gpm)

Mag

Meter

Error

Acoustic

Meter

(gpm)

Acoustic

Error

1 10 1 3002 22455 2246 2197 ‐2.2% 2310 2.9%

2 11 1 3002 22455 2041 2143 5.0% 2233 9.4%

3 10 0.8 2401 17964 1796 1757 ‐2.2% 1848 2.9%

4 15 1 3002 22455 1497 1440 ‐3.8% 1519 1.4%

5 14 0.3 901 6737 481 468 ‐2.8% 497 3.4%

T1 14 1 3002 22455 1604 1777.25 10.8% 1875 16.9%

T2 22 1.4 4203 31437 1429 1363.222 ‐4.6% 1432 0.2%

T3 17 0.8 2401 17964 1057 1070.375 1.3% 1152 9.0%


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Appendix D

Calculations

∆ 1:52 1:42 10

∆ 17.3 16.3 1

∆ ∆ ∗ 1 ∗3056 ∗ 7.48 22860

∆∆ 22860

10 2286

2286 2207

2286 3.5%

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