EPA-R2-73-145
MARCH 1973
Environmental Protection Technology Series
A Thermal Wave Flowmeter
for Measuring
Combined Sewer Flows
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
U. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-R2-73-145
March 1973
A THERMAL WAVE FLOWMETER FOR MEASURING
COMBINED SEWER FLOWS
By
Paul W. Eshleman and Robert A. Blase
Project 11020 EYD
Project Officer
Harry C. Torno
Office of Research and Monitoring
Environmental Protection Agency
Washington, D. C. 20460
Prepared for
OFFICE OF RESEARCH AND MONITORING
U. S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D. C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.G. 20402
Price $1.25 domestic postpaid or $1.00 GPO Bookstore
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EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency, and approved for publication.
Approval does not signify that the contents necessar-
ily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or
recommendation for use.
I!
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ABSTRACT
A study of the application of thermal techniques to the measurement
of flow rates in combined sewers has been conducted. The utiliza-
tion of flush-mounted hot wire or hot film anemometers in a direct
reading mode was extensively investigated. It was concluded that
such a direct reading application was not feasible due to shifts in
calibration caused by the build-up of contamination and the lack of
commercially available units with sufficient ruggedness and reliabil-
ity for application in a combined sewer pipe.
A particular technique, which is based upon measuring the time-of -
flight of thermal pulses generated at various positions around the
periphery of the pipe, was investigated in depth. A full scale proto-
type unit using five thermal wave sensors distributed around one-
half of the circumference of the pipe was fabricated and tested.
These tests indicated that the present configuration does not provide
signals which have adequate precision to enable this unit to measure
the fluid flow with the desired accuracy.
This report is submitted in partial fulfillment of Contract No. 14-12-
911 under the sponsorship of the United States Environmental Pro-
tection Agency.
111
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CONTENTS
Section
I Conclusions 1
II Recommendations 3
HI Introduction 5
IV Literature Search Results on Hot Film
Anemometry 7
V Thermal Wave Flowmeter Design Concept 21
VI Hydraulic Considerations 25
VII Results of Preliminary Laboratory Experiments
Utilizing Thermal Wave Flowmeter 29
Vni Detailed Prototype Design 45
IX Preliminary Flowmeter Calibration 51
X Full Scale Test Site Selection 59
XI Full Scale Flowmeter Calibration 63
XII Acknowledgements 65
XHI References 67
XIV Appendices
A List of Vendors 81
B Design Drawing List 83
C Strut Flowmeter Test at NSRDC 85
D Flowmeter Test at National Bureau
of Standards 95
v
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FIGURES
Figure Page
1 Commercial configurations of hot wire and hot
film anemometers 9
2 Schematic of constant current system 10
3 Schematic of constant temperature system 12
4 General sensor configuration 22
5 Model test sensor block 30
6 Model test hydraulic apparatus 32
7 Experimental instrumentation for model flow tests 33
8 Thermal wave velocity versus mean velocity for
the sensor block on the side of a 1-inch I. D. pipe 35
9 Thermal wave velocity versus mean velocity for
the sensor block on bottom of 1-inch I. D. pipe 36
10 Thermal wave velocity versus mean velocity for
sensor block on top of 1-inch I. D. pipe 37
11 Thermal wave velocity versus mean velocity for
sensor block on side of 2-inches I. D. pipe 38
12 Thermal wave velocity versus mean velocity for
sensor block on bottom of 2-inches I. D. pipe 39
13 Thermal wave velocity versus mean velocity for
sensor block on side of 2-inches I. D. pipe
with wedge 40
14 Thermal wave velocity versus mean velocity for
sensor block on side of 1-inch pipe with wedge 41
15 Thermal wave velocity versus mean velocity for
all configurations 42
VI
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Figure Page
16 Full scale sensor block in cross-section 46
17 Proposed sewer pipe installation of flow
measurement system 47
18 Calibration data 54
19 Electrical calibration data 55
20 NSRDC calibration data (sensor #2) 92
21 Electrical calibration (actual time delay versus
reading of the instrument) 100
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TABLES
Table Page
1 Instrument electrical calibration 53
2 Scott's Run hydraulic characteristics 61
Vlll
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SECTION I
CONCLUSIONS
1. A study of the application of thermal techniques to the measure-
ment of flow rates in combined sewers has been conducted, and it
is concluded that extending the application of hot-film anemometry
techniques from fluid mechanics research to a commercial applica-
tion of measuring contaminated sewer effluent for extended periods
of time does not appear feasible. The major reasons are:
a. the change in calibration that occurs due to contam-
ination film build-up;
b. the breakdown of protective coatings over long periods
of time; and
c. the change in calibration that occurs due to dissolved
gases coming out of solution and depositing on the film
element as bubbles.
2. A particular technique incorporating a heat source and sensor
located a known distance apart which can measure the time of flight
of a thermal pulse has been indicated feasible in scale model labora-
tory tests.
3. A prototype configuration for a full scale demonstration model
was developed. It contained features to minimize sensitivity and
data scattering problems observed during early scale model labora-
tory experiments. The full scale tests have indicated these problems
to be greater than noted in the model tests.
4. A calibration of the prototype unit has been attempted and has
demonstrated the capability of this unit to indicate flow rates. How-
ever, the calibration data indicate that certain flow factors affect the
instrument's performance to such an extent that the desired accuracy
cannot be achieved with the unit in its present configuration.
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SECTION II
RECOMMENDATIONS
An investigation of a flowmeter concept based upon the monitoring of
the flow in the boundary layer has been concluded. This concept of a
non-invasive flowmeter was based upon the measurement of the time
of flight of a thermal pulse. The preliminary calibrations which were
conducted indicated that the accurate measurement of fluid flow by the
non-intrusive means of injecting a small thermal pulse into the fluid
at its boundary layer is not presently feasible. The dissipation of
heat was determined to be quite large, as was the ratio of the average
stream velocity to the apparent boundary layer velocity. Future
examinations of non-invasive thermal flowmeters must deal with the
problems of adequate boundary layer penetration, minimal thermal
lag, and adequate protective coating over the heater element. In addi-
tion, power densities in excess of the 300 watts/square inch (instan-
taneous value) utilized in this approach must be examined.
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SECTION III
INTRODUCTION
This is a final report submitted to the Environmental Protection
Agency and contains the results of work conducted under Contract
No. 14-12-911. The objective of the contract was to demonstrate the
feasibility of a thermal wave flow measuring device to provide for
the continuous measurement and recording of_flow_s_ in existing storm
and combined sewers without disrupting the capabilities of the sewer.
Phase I of the contract consisted of a literature search, feasibility
study, and a proposed full scale design of the flow measuring system.
Phase II consisted of fabrication and preliminary testing of elements
of the full scale prototype, and Phase III consisted of full scale
testing and evaluation of prototype feasibility.
The proposed flow measurement system had a design goal of meas-
uring the volume flow rate in the sewer within five percent of its
actual value over the flow range. The volume flow rate is computed
by making two measurements:
1. The average flow velocity in the pipe, and
2. Area of flow as determined from a stage measurement.
The design range for measuring the average flow velocity encompassed
a stage/diameter ratio of 0. 067 through pressurized full channel flow.
The stage measurement capability ranges from stage/diameter ratios
from zero to one with continuous readout capability in between. Re-
liable operation for a life of at least one year was desired. Data
readout into a simple low-cost recorder with the information in a
form suitable for data processing was also provided. Minimum pro-
trusion into the flow was a design requirement and no sharp edges or
snaggable protrusions were permitted.
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The original proposed concept of operation was to utilize a series
of flush mounted hot-film anemometers configured along the wall
of the sewer pipe. The forced convective heat transfer from the
anemometers would then be a measure of the average velocity in
the pipe. After studying the results of the literature search and
conversations with researchers and vendors, it was concluded
that the originally proposed hot-film measuring system could not
maintain a constant calibration due to contamination inherent in
the sewer environment.
A new concept which relied on the correlation of the velocity of a
heat wave generated at the periphery of the pipe to the average
velocity was then studied and the concept was experimentally vali-
dated in a 1-inch and 2-inch I. D. pipe. A detail design of the flow
measurement system utilizing the thermal wave concept was then
completed and a prototype device was fabricated and tested.
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SECTION IV
LITERATURE SEARCH RESULTS
ON
HOT FILM ANEMOMETRY
The literature search was conducted with the intent of obtaining the
latest information on the development, manufacturing techniques, past
applications, and experimental data on the use of hot-film anempmetry
for velocity and flow measurement of liquids. The literature search
was composed of the following areas
1. Personal Contact
a. Vendor Companies
b. Researchers
2. Vendor Catalogs and Publications
3. Technical Reports
4. Symposium and Conference Reports
5. Thesis Publications
6. Textbooks
A detailed listing of the research literature is contained in Section
XI and references in the text are numbered in conjunction with the
listing contained in Section XI. The following section is separated
into (1) Theoretical Principles of Anemometry; (2) Survey of Past
Applications of Anemometry; (3) Survey of Vendors; (4) Survey of
Technical Discussions; and (5) Conclusions.
THEORETICAL PRINCIPLES OF ANEMOMETRY
When an electrically heated wire or film is placed in a flowing fluid,
heat will be transferred between the two, depending on a number of
factors, including the flow rate. This type of flow sensing element .
-------
is called a hot-wire or hot-film anemometer. Typical commercial
configurations of these are depicted in Figure 1.
The cooling of the film is a function of the velocity of the flow;
temperature, density, viscosity, and thermal conductivity of the fluid;
temperature, diameter, and length of the film backing material; and
thickness of the film. If all but one of the fluid flow and film variables
are kept constant, the heated film is a transducer for measuring the
remaining variable. For variable fluid properties, as would be
experienced in sewer effluent, the problem of constant calibration
would be nearly impossible.
The convective heat transfer from a cylinder has had extensive
theoretical and experimental study. The potential flow solution is
attributed to King. The King's law relation may be expressed as;
2
I R r-
w = A + BVU (1)
R -R
w a
in which:
I = electric current
Rw = electrical resistance of wire at wire temperature
Ra = electrical resistance of wire at fluid temperature
A, B = coefficients
U = velocity of flow
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HOT WIRE
FINE WIRE
-TUNGSTEN
-PLATINUM
-PLATINUM ALLOY
-GOLD PLATED
STAINLESS STEEL
SUPPORTS
1234 WEDGE FILM SENSOR
SIDE
FLOW
WEDGE
0.121
--PLATING TO DEFINE
SENSING LENGTH
CYLINDRICAL HOT FILM (STANDARD SUPPORTS)
GOLD PLATED
STAINLESS STEEL
SUPPORTS
-GOLD PLATING DEFINES
SENSING LENGTH
-QUARTZ COATED PLATINUM FILM SENSOR
ON GLASS ROD (O.OOl" TO 0.006" DIA.)
CONICAL HOT FILM
pQUARTZ
QUARTZ COATED
PLATINUM FILM
BAND—,
GOLD FILM
ELECTRICAL LEADS
CYLINDRICAL HOT FILM (SINGLE ENDED)
CANTILEVER SUPPORTED SENSOR
MADE FROM GLASS TUBE
QUARTZ COATED
PLATINUM FILM
(O.O025"TO 0.006"
DIA.)
GOLD WIRE COMES
THROUGH INSIDE OF
SENSOR TO MAKE END
ELECTRICAL CONNECTION
STAINLESS STEEL
SUPPORTING
TUBES
PARABOLIC HOT FILM
-GOLD PLATING DEFINES
SENSING LENGTH
DUARTZ COATED
PLATINUM FILM
ON LEADING EDGE
GOLD FILM
ELECTRICAL LEADS
WEDGE HOT FILM
QUARTZ ROD
GOLD FILM ELECTRICAL LEADS
-QUARTZ COATED PLATINUM
FILM (0.004"* 0.040" EACH SIDE)
FLAT SURFACE HOT FILM
QUARTZ COATED ,
HOT FILM I !''
ON SURFACE
STAINLESS STEEL TUBE SHIELDING QUARTZ ROD
Figure 1. Commercial Configurations of Hot Wire and
Hot Film Anemometers.
9
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It has been found that, at best, King's law only holds for continuum
flow at large Reynolds numbers. For continuum incompressible
flow, the best experimental relation between mean heat loss and
mean velocity is
i2
R
w
R (R -R0)
w w a.
= A+ BU11
(2)
This relation is similar to King's; however, n is a function of the fluid
medium, overheat ratio, sensor, and mean velocity. Again, cali-
bration accuracy can only be maintained in closely controlled
experiments.
Two methods are employed to measure flow. The first technique
employs a constant current passing through the sensing wire. Varia-
tion in flow results in changed wire temperature; hence, changed
resistance, which thereby becomes a measure of flow. The electri-
cal schematic of a constant current system is shown in Figure 2.
OUTPUT OF AMPLIFIER
o
MANUAL
BALANCE
=s CONSTANT
OUTPUT
-10
ffl
lil
Q
•-20
-30
X
NON-LINEAR
AMPLIFIER
HOT
WIRE
a.
•£.
-40
-50
10'
10° 10
FREQUENCY (Hz)
Figure 2. Schematic of Constant Current System.
10
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The current to the sensor is maintained essentially constant by using
a large resistor in series with the sensor. The current is selected
so the sensor is operated at the desired temperature in the environ-
ment of interest. If the heat transfer between the environment and
the sensor increases (due, for example, to an increase in velocity)
the sensor will tend to cool with a resulting decrease in its resis-
tance. The major drawback of the constant current system is that
the frequency response of a sensor depends not only on sensor
characteristics, but also on flow characteristics. The response
depends on both the thermal capacity of the sensor and the heat
transfer coefficient between the sensor and its environment. Since
the sensor response changes witjj changes in flow (changing the heat
transfer coefficient), the frequency compensation of the amplifier
must be readjusted whenever the mean flow changes. This is not
practical for the sewer flow application.
The constant temperature type of compensating circuitry overcomes
the primary disadvantage just mentioned in the constant current
system by using a feedback loop. Figure 3 depicts a constant
temperature system. As the velocity past the sensor increases,
the sensor will tend to cool with a resulting decrease in the resis-
tance. This resistance decrease will cause the voltage to decrease;
thus, changing the input to the amplifier. The phase of the amplifier
is such that this decrease in voltage will cause an increase in the
output of the amplifier in order to increase the current through the
sensor. The output of the constant temperature system is the
voltage output of the amplifier which in turn is the voltage required
to drive the necessary current through the sensor. Due to the
feedback action, the resistances in the bridge remain constant. The
voltage across the bridge is directly proportional to the current
through the sensor and power is equal to the current squared times
11
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the resistance. Therefore, the square of the voltage measured on top
of the bridge is directly proportional to the instantaneous heat transfer
between the sensor and its environment.
BRIDGE
VOLTAGE
OUT
CONTROL
RESISTOR
I
- 1
D-C DIFFERENTIAL
AMPLIFIER (G)
SENSOR
Figure 3. Schematic of Constant Temperature System.
There are special considerations for hot-film sensors used in liquids
which greatly limit their application:
Contamination -The characteristics of combined sewer waste -
water will cause prohibitive contamination on the hot-film sensor
that would drastically change the heat transfer capability of the
film. In turn, measured voltages would be unstable for a given
flow velocity and be inapplicable in terms of comparison to a
12
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previous calibration. Oils, greases, and soaps contained in sewer
wastewater would be most detrimental to achieving stable measure-
ments. They tend to coat the wetted surfaces of the sewer pipe by
congealing, and in doing so on the sensor film, would cause a change
in the heat transfer characteristics of the film. Dissolved gases in
the wastewater such as carbon dioxide, if near saturation levels,
will be driven out of solution by the heated sensor since saturation
levels decrease with increasing temperature. Bubbles, thus formed
will cling to the sensor surface and cause erratic heat transfer.
Water is the major component of the sewer effluent and will undergo
electrolysis unless the hot film is completely insulated from the
water. Electrolysis forms gas bubbles and drives dissolved minerals
out of solution to deposit on the sensing elements. The grit content in
the combined sewer wastewater will greatly accelerate the break-
down of the film insulation. The grit content is greatly increased
during storm runoff and therefore excessive wear would be
expected.
Temperature Changes - Since the operating temperature of a
sensor in liquids is limited to the boiling point and more practically,
to an increase over the fluid temperature of 50 to 100°F, small temp-
erature changes can provide significant errors with constant
temperature anemometer operation. For example a 5°F change with
an overheat of 50°F gives about a 10 percent change in output. In
gases where sensor temperature is typically 400-500°F above the
fluid temperature, small temperature changes are not so significant.
Hence, in liquids some method of temperature compensation is
important. There are means of achieving this but at added cost and
reduced reliability.
13
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SURVEY OF PAST APPLICATIONS OF HOT-FILM ANEMOMETRY
IN WATER
Ling (55) introduced the hot-film probe for use in liquid flows in 1956.
Since then a number of investigations have been carried out in liquids
with only a few being successful. In most of these, the film was placed
away from the wall since its size can interfere with the detailed
measurements required in the sub-layer region (43) and (53). Indeed,
different configurations of film probes have produced very different
results within the same experiment even for the simple case of meas-
uring velocity profiles in turbulent flows (44) and (22).
The one type of film probe that holds promise of being applied to
sewer flow is the flush mounted probe because the backing material
does not interfere with the flow field and has the best chances of
physical survival in the sewer environment. Very little research has
been done to determine the feasibility of using flush mounted, hot-film
sensors for quantitative measurements in water because the electrol-
ysis problem has only recently been solved through the use of quartz
coatings. Townsin (45) demonstrated the use of the flush mounted
hot-film sensor to detect laminar, transition, and turbulent flow
fields along the hull of a ship model. Similarly, Burns and Murphy
(46) used the same type of probe to investigate the effectiveness of
turbulence stimulation on ship models. Rundstadler (30) used them
for studies of the viscous sublayer. An attempt to calibrate them for
shear stress measurements was unsuccessful, however, because of the
low velocity and electronic drift problems.
Hot-film sensors have also been used for quantitative turbulence
measurements. Dreyer (22) and Fabula (32) have also explored this
area using conical and parabolic hot-film probes. Geremia (26)
14
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studied the flush mounted hot-film anemometer as a possible tool in
turbulence research and found it to be a powerful measuring device.
Mies (27) studied the most effective way ol curve fitting hot-film
measurements made in an open channel for purposes of calibration.
Richardson and McQuivey (36) describe a method for measuring
turbulence in water which does not depend on filtering and the removal
of gases from the water. The method is based on the discovery that
the change in the voltage/velocity relation by contamination of the
probe is the same as the change which occurs for an uncontaminated
probe when the overheat ratio is decreased.
Resch (38) made measurements of the relative intensity of turbulence
and energy spectra using a conical probe at the axis of a cylindrical
pipe. The results of these measurements were compared with those
of other researchers in air and in dynamically similar flows. The
comparison shows that measurements of turbulence can be carried out
in water with a comparable degree of accuracy to those carried out in
air. Almost every investigator was concerned with contamination and
took careful measures to filter or otherwise reduce the effects of this
problem.
Runstadler (30) gives a very concise summary of the factors that
significantly affect the stable non-drift operation of hot-film probes
in water.
Dirt Contamination - Lint, dirt particles, and even particles micro-
scopic in size can collect on the probe or sensing element causing a
change in the heat transfer characteristics between the probe and
the fluid.
Dissolved Gases - Air or other gases in saturation in the water may
come out of solution and collect on the probe or sensing element,
causing a change in the heat transfer characteristics between probe
15
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and fluid. This factor is enhanced when the probe is operated at
large overheats.
Chemical Impurities - Chemical impurities in the water such as
chlorine or similar halogens, may produce a chemical reaction with
the film sensing element, and cause eroding of the metal film thus
producing a change in the electrical resistance and heat transfer
characteristics. In addition, hard water forms deposits on the probe
element that alter the heat transfer characteristics between the
probe and fluid.
Water Electrical Conductivity - A high electrical conductivity caused
by impure water can lead to a low parallel resistance path through
the water relative to the resistance of the film, thus producing an
effective change in the resistance of the sensing element. An
important consideration in this regard is to minimize the leakage
current which can occur by using a thin protective coating. This
has the adverse affect of reducing sensitivity but is a necessity for
prolonged operation. As yet, reliability has not been achieved in
coatings for prolonged operation.
Stray Electric or Magnetic Fields - Stray electric or magnetic fields
(stray electric fields frequently occur in water channel flows) may
have an affect on the stable operation of probes. At present, little
is known about this factor.
Nucleate Boiling - The probe must be operated at sufficiently low
values of overheat such that formation of water vapor caused by
nucleate boiling does not occur on the sensing element.
A number of factors pertaining to the construction and operation of
the probes are also important through their affects on the factors
described in the preceding.
16
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Probe Shape - The shape of the probe can be important by providing
a probe form that is less susceptible to collecting dirt and more
readily sheds gas or vapor bubbles.
Electrode Surface Area - The surface area of the electrode should
be kept small and the location of the electrode on the probe should
provide the longest possible conduction path for leakage current flow.
Shielding of Electrodes - As previously mentioned, one way of pre-
venting electrolysis is by coating the electrode. Experience has
shown however, that electrolysis may occur under the coating, pro-
ducing gas bubbles which can lead to an early breakdown of the
electrode material and coating.
Electrode Material - Experience has also shown that platinum sponge
material sometimes has a tendency to break down and decompose
after long use in water. The effect is to produce an increase in the
electrical resistance of the probe. Other materials used for films
are Tungsten, Nichol, and an alloy of Platinum (80%) arid Iridium
(20%).
In almost every report that was reviewed some mention of probe
contamination was made. Careful filtering and deaerating techniques
were developed to have a test fluid that would not contaminate the
measuring probe and thus cause a calibration shift. Needless to say,
investigation of other means of measuring velocity in the sewer was
begun when it became apparent that contamination was such a severe
limitation.
17
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SURVEY OF VENDORS OF HOT-FILM ANEMOMETERS
A list of all vendors contacted during the study (see Appendix A)
revealed that only three were actively in the business of manufacturing
hot-film and hot-wire anemometers and are:
DISA Electronics
779 Susquehanna Avenue
Franklin Lakes, New Jersey 07417
201-891-9460
Thermo-Systems, Inc. (TSI)
2500 Cleveland Avenue, North
Saint Paul, Minnesota 55113
CGS/Datametrics
127 Coolidge Hill Road
Watertown, Massachusetts 02172
617-924-8505
These companies were personally visited and interviewed with the
intent of establishing the level of expertise and facilities dedicated to
this field and to obtain literature and personal opinions toward the
application of hot-film sensor for measuring sewer flow. The results
of these meetings are contained in the next section.
Of these three companies, DISA and TSI are rated about equal in
expertise and facilities. CGS did not appear to be as actively engaged
in this field as the other two companies. TSI has all of its facilities
located in one location whereas DISA has manufacturing and assembly
plants in Herlev, Denmark, with sales and marketing located in
New Jersey. Impressions made from conversations with anemometer
users and the literature survey indicate that both TSI and DISA
manufacture good quality equipment.
SURVEY OF TECHNICAL DISCUSSIONS
In order to obtain first-hand knowledge of the manufacturing techniques
ised in making hot-film anemometers and to personally inspect the
18
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facilities of proposed vendors, it was felt necessary to visit the
respective companies. This proved to be a very fruitful decision
not only from the fulfillment of the stated intent but many additional
sources of information were identified in terms of literature and
researchers as a result of the meetings. In addition, professional
suggestions on the application of hot-film anemometry to measuring
sewer flow were obtained. A survey of obtained information is pre-
sented in the following.
To protect the probe from abrasive wear, an extra thick industrial
coating will be required. Sensitivity and frequency response will be
sacrificed for this addition.
Coatings are mostly sputtered quartz, however, teflon and zirconium
oxide have been experimentally tried with varying success.
Self-cleaning systems that have been examined are mechanical
scrubbers, excessive overheating to burn off deposits, and ultrasonic
cleaning techniques. Overheating is not practical for flush mounted
hot-films because of loss of heat to the substrate. Mechanical
scribbers are not feasible because of the interference caused in the
flow and lack of repetitive cleaning ability over long periods of time.
Ultrasonic cleaning is the most promising; however, it would entail
a costly development with uncertain results.
Static pressure does not affect the calibration of the probe in water
(+2%) up to 1000 psi.
Calibration of probes in water is normally accomplished in an or if iced
free stream, jet, a towing tank, or rotating tank of water.
The effect of using a larger sensor would be increased sensitivity
which means a heavier coating could be applied; however, disadvan-
tages are increased power requirements, reduced frequency response,
19
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thermal expansion problems, and increased stabilization time due to
the larger amount of substrate.
Probe operation in still air presents no problem when the overheat
ratio is set up for water.
If several probes and multiplexing is used, recommended stabilization
times were estimated anywhere from 0. 7 seconds to 15 minutes!
There is no existing past experience to indicate that activating for
short periods and deactivating for long periods of time would be
harmful.
The general independent consensus from all three manufacturers
after extensive questioning is that no off-the-shelf probe now exists
that could be expected to work in a sewer environment for more than
hours or days at the most. The majority of applications for hot-film
anemometers are for basic fluid mechanics research under laboratory
type conditions. There is some history of industrial application (pulp
slurries, power plant effluent) of hot-film sensors as one-shot
measurements. Probe longevity was very short in these instances.
The manufacturers are anxious to develop a reliable industrial type
probe for liquids but a breakthrough in the near future is not
anticipated.
20
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SECTION V
THERMAL WAVE FLOWMETER
PRELIMINARY DESIGN CONCEPT
The thermal wave flowmeter correlates the time of flight of a thermal
wave between two fixed points to the average flow velocity in the pipe.
The basic sensor elements are depicted in Figure 4. The thermal
wave in the fluid is generated by a heater element that is heated with
a periodic voltage. The flow passing over the heater transports the
wave downstream at some propagation velocity which is a function of
the average velocity in the pipe. A thermistor element downstream
senses the passing of the thermal pulse. An electronic counter is
triggered when the pulse is generated and stopped when the pulse is
sensed by the thermistor element. The distance between the heater
and the thermistor, divided by the propagation time measurement, then
determines the propagation velocity.
A separate stage measurement of the flow, utilizing electrical conduction
techniques, is used to complement the flow velocity measurement in order
to determine the volume flow rate. This unit is comprised of two stain-
less steel rods molded into a rubber mold which is then mounted in the
sewer pipe.
The flow measurement system incorporates five thermal sensors mounted
on the periphery of the pipe. The measurement of the average flow
velocity in the pipe is obtained by averaging the longitudinal propagation
velocities of the five thermal waves generated at the five symmetric
peripheral positions. The averaging technique will compensate for
irregular velocity profiles in the pipe caused by blockages, closing of
valves, etc., and will give an accurate means of evaluating the average
velocity. Surface contamination which was severely detrimental to the
direct measuring hot-film anemometer technique will not affect the
thermal wave except in magnitude of signal which the measurement
21
-------
HEAT PULSE TAKES TIME t TO
TRAVEL FROM HEATER TO
SENSOR
HEATER
HEAT
SENSOR
Figure 4. General Sensor Configuration
22
-------
system does not rely on. Of course there is a minimum signal
required such that signal-to-noise ratios are of sufficient level to
properly activate the data gathering electronics.
The electronic portion of the system is designed by utilizing inte-
grated circuits to monitor the thermistor signals from the sensor
blocks. A correlator circuit is employed to derive the heater signal
waveform. The sensor phase delayed outputs are then multiplexed
together with the time of day and recorded. A portable cassette
type recorder is used to record the sensor data on-line for
approximately one week before a tape change is required. The data
is recorded in a format that is adaptive to high speed data process-
ing. The sampling of the volume flow rate is logically programmed
such that higher rates are used during high flow conditions (i. e.,
during peak or storm conditions) and low sampling rates are used
during low flow conditions.
23
-------
SECTION VI
HYDRAULIC CONSIDERATIONS
Hydraulic ally, the flow of wastewater in a sewer may be classified as
either open-channel or pressure-conduit flow. The two kinds of flow
are similar in many ways but differ in one important respect. Open-
channel flow must have a free surface, whereas pipe flow has none,
since the water must fill the whole conduit. A free surface is subject
to atmospheric pressure. Pressure-conduit or pipe flow, if cross
section is circular, exerts no direct atmospheric pressure but
hydraulic pressure only.
Sanitary sewers often are designed as open channels, that is, with a
free surface for ventilation reasons or to provide an additional factor
of safety. However, some are designed to flow just full at peak design
flow, since there will be a free surface for ventilation at all lesser
flows. There are many empirical methods to evaluate the flow in a
sewer under various conditions. Darcy-Weisbach, Kutter, Hazen-
Williams, and the Manning formulas are all well known and utilized
for design of sewer systems. However, these formulae are empirical
in nature and, due to the local velocity distribution at a particular
measuring station, cannot be relied upon to give accurate flow data.
For example, local blockage may cause a high stage of low flow with
a much slower velocity than that predicted by the classic formulae.
Therefore, in order to obtain an accurate responsive measurement
system, it is necessary to measure both the average velocity in the
pipe and the stage of flow. The volume flow is then simply:
Q = VA (3)
where Q = volume flow rate
V = mean velocity of the flow cross section
A = flow cross sectional area which is a function of the stage
of flow.
25
-------
The measurement of the average velocity is indeed the most difficult
task in the development of an accurate flow meter. Because of the
solids contained in combined sewer flow, it is imperative that nothing
interfere with the cross section of the flow; otherwise the physical
longevity would be very short.
Owing to the presence of a free surface, friction along the pipe wall,
and local blockage, the velocities in a channel are not uniformly
distributed in the channel section. The velocity distribution in a
channel section depends also on other factors, such as the shape of
the cross section, the roughness of the channel, presence of bends,
and presence of other pipe connections in the vicinity. The measured
maximum velocity in open channels usually appears to occur below the
free surface at a distance of 0. 05 to 0. 25 of the depth. In a broad,
rapid, and shallow stream or in a very smooth channel, the maximum
velocity may often be found at the free surface. The roughness of the
channel will cause the curvature of the vertical-velocity distribution
curve to increase. On a bend, the velocity increases greatly at the
convex side, owing to the centrifugal action of the flow. Laboratory
investigations have found that flow in straight prismatic channels is
in fact three dimensional manifesting a spiral motion, although the
velocity component in the transverse channel section is usually small
and insignificant compared with the longitudinal velocity components
(58), (59), (60), (62).
As a result of the previous discussion, the implied requirement in
making an average flow measurement in an open channel is that
several measurements must be made which correlate to various
portions of the cross sectional flow area. These measurements can
then be averaged and correlated to the mean flow rate in the pipe.
26
-------
The present measurement system is composed of several longi-
tudinal velocity measurements at the periphery of the pipe which,
when averaged, will correlate to the mean velocity of the flow cross
section. A separate device to measure the stage of flow will then
provide the necessary measurements for determining the volume
flow rate.
27
-------
SECTION VII
RESULTS OF PRELIMINARY LABORATORY EXPERIMENTS
UTILIZING THERMAL WAVE FLOWMETER
In order to gather experimental data utilizing the concept of the
thermal wave flowmeter, it was agreed between EPA and HCI to
extend the time of Phase I. During that time, HCI fabricated and
tested sensor blocks for a 1-inch and 2-inch I. D. pipe. Average
flow velocities in the 1-inch I. D. pipe ranged from 1. 0 to 5. 5 ft/sec
or Reynolds numbers from 6850 to 37, 700. Average flow velocities
in the 2-inch pipe ranged from 0. 5 to 1. 6 ft/sec, or Reynolds num-
bers from 6850 to 21, 900. The purpose of the experiments was to
determine the characteristics of the thermal wave flowmeter as a
function of average flow velocity, peripheral position in the pipe and
pipe diameter. Measures of evaluation are in terms of sensitivity
and repeatability.
Sensitivity is defined as the ratio of the thermal wave propagation
velocity to the average fluid velocity in the flow cross section.
The Sensitivity of the 2-inch I. D. pipe data was approximately 70
times greater than that for the 1-inch pipe (0. 035 compared with
0. 0005). Thus, the thermal wave propagation velocity increases
0. 035 ft/sec for every increase of 1 ft/sec in average flow velocity
in the 2-inch pipe. The model test data demonstrated a need for
improved sensitivity and reduction in scatter, which should be
available in the full scale model with the proposed full scale design.
The basic sensor block used in the experiments, depicted in
Figure 5, was flush mounted on the periphery of the pipe. The
thermal wave in the fluid was generated by a nichrome wire that
29
-------
V,"-
H
l7/32
COMPENSATING THERMISTORS
HEATER
SENSING THERMISTOR
I R
Figure 5. Model Test Sensor Block.
30
-------
was heated periodically. The thermal wave was sensed by a
thermistor whose distance, d, from the heater was fixed and
accurately known. The heater temperature was raised approx-
imately 80 C which causes approximately a 1° C rise in the water
passing over the downstream sensor. The time of flight of the
thermal wave when divided into the separation distance, d, deter-
mines the value of the local propagation velocity.
Figure 6 depicts the hydraulic apparatus used to conduct the experi-
ment. Both the 1-inch LD. pipe and 2-inch I. D. pipe were used
during the tests. Average velocity was measured with a Fischer
Porter No. 102732 lab rotameter with fluid velocity being maintained
with a constant head supply. The magnitude of flow velocity was
controlled by a series of valves as shown. The sensor block was
flush mounted in the tube approximately 6-inches from the reservoir
end such that pipe entrance affects were negligible and fully devel-
oped turbulent flow existed over the sensor block.
The assembled instrumentation is indicated in Figure 7. Two
thermistor beads and a nichrome wire heater were assembled into
an aluminum block with the spacing indicated on Figure 5. The heater
was supplied with a varying amplitude power wave whose frequency
was determined by a low frequency oscillator. The driving frequency
was varied initially to determine the best signal-to-noise ratio. All
test data were taken at 0. 5 Hz by utilizing a square wave voltage
into the heater. A thermistor bridge with a temperature compen-
sating network was installed in the sensor block. A preamplifier
to provide a high level signal was connected to the output of the
sensor network and the signal fed to the filter network. The
output of the filter was fed to a zero crossing detector and a square
31
-------
CONSTANT HEAD SUPPLY
1-- i.O.PVC PIPE
FISCHER PORTER
NO.102732 LAB
ROTAMETER
CAPACITY
2.8-35.6PM
SENSOR BLOCKS
(5°6"FROM PIPE ENTRANCE)
- GATE VALVE
MAXIMUM VELOCITY = 6 FT/SEC.
RESERVOIR
Figure 6. Model Test Hydraulic Apparatus
-------
LOW
FREQUENCY
OSCILLATOR
I
i
HEATER
co
GO
THERM
SENSOR
PERIOD
COUNTER
SHARER
Figure 7. Experimental Instrumentation for Model Flow Tests.
-------
wave is generated with a duty cycle proportional to the time between
the positive going zero crossing of the heater and the sensor. A
counter was used to determine the time-of-flight of the thermal wave.
Each data point was derived from averaging ten consecutive readings
from the counter.
TEST RESULTS
The test results are contained in Figures 8 through 14. The graphs
plot the thermal wave propagation velocity versus the average or
mean flow velocity in the pipe. The curves were determined by
using a least squares curve fit. The following observations are
made concerning the graphs.
1. The sensitivity for the 1-inch I. D. pipe data is very low
(0.0005).
2. The sensitivity of the 2-inch I. D. pipe data is approximately 70
times greater than the 1-inch pipe data (0. 035).
3. Data from various peripheral positions appeared very similar;
that is the flow appeared axisyrnmetric.
4. Inserting a flow wedge ahead of the sensor block in the 1-inch I. D.
pipe increased the thermal propagation velocity by a factor of two
but did not change the sensitivity appreciably.
5. Inserting a flow wedge ahead of the sensor block in the 2-inch
I. D. pipe did not appreciably affect the thermal wave propagation
velocity but lowered the sensitivity from 0. 035 to 0. 02.
DISCUSSION OF TEST RESULTS
The graphs of the flow data clearly indicate the ability of the thermal
wave concept to measure average flow velocity, but, at the same time
illustrate some unknown elements in the present model test configur-
ation. The following is concluded from the test results.
34
-------
H.030
t .029
O
3
.028
Z
O
.027
en
o >026
a:
o.
uj -025
. .024
£E
UJ
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0
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234
MEAN VELOCITY (FT./SEC)
Figure 8. Thermal Wave Velocity Versus Mean Velocity for the
Sensor Block on the Side of a 1 -inch I. D. Pipe.
-------
o
LU
CO
.030
O .029
O
.028
.027
Q.
UJ .026
cr
CL
It1 .025
.024 -
QC
UJ
I
O
234
MEAN VELOCITY (FT/SEC)
ure 9» Thermal Wave Velocity Versus Mean Velocity for the
Sensor Block on Bottom of 1-inch I. D. Pipe.
-------
CO
I-
U.
O
o
.030 -
.029
.028
9. .027
<
CD
< .026
O
oc
LU
.024
QL
UJ
X
o
234
MEAN VELOCITY ( FT/SEC)
Figure 10. Thermal Wave Velocity Versus Mean Velocity for
Sensor Block on Top of 1-inch I. D. Pipe.
-------
CO
.070
O
UJ
CO
\
h-
.060
O
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UJ
.050
< .040
Q.
o
cr
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.030
cc
LJ
X
_L
_L
_L
0.25
0.5 0.75 1.00
MEAN VELOCITY ( FT/SEC)
1.25
1.50
Figure 11. Thermal Wave Velocity Versus Mean Velocity for
Sensor Block on Side of 2 -inches I. D, Pipe.
1.75
-------
CO
CD
.07 -
O
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.06
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££.
UJ
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T
0.25
0.5 0.75 1.0
MEAN VELOCITY ( FT/SEC)
1.25
1.50
1.75
Figure 12. Thermal Wave Velocity Versus Mean Velocity for
Sensor Block on Bottom of 2 -inches I. IX Pipe.
-------
.07
UJ .06
CO
O
O
_l
UJ
g -04
o
cc
Q_
UJ
^ -03 -
cc
UJ
X
h-
0
o
0.25
Figure 13.
0.5 0.75 1.00
MEAN VELOCITY (FT/SEC)
1.25
1.50
1.75
Thermal Wave Velocity Versus Mean Velocity for Sensor
Block on Side of 2-inches I. D. Pipe With Wedge.
-------
LJ -065
O .060
O
_1
LJ
o
< .055
e>
CL
o
cc.
a.
> .050
<
o:
UJ
i
8
H
0
1 23456
MEAN VELOCITY (FT/SEC)
Figure 14. Thermal Wave Velocity Versus Mean Velocity for Sensor
Block on Side of 1-inch Pipe With Wedge.
-------
to
.07
O
UJ
.05
_J
UJ
< .04
Q.
O
01
a.
UJ
cc
!£ .02
I- J~
T.
0
2" I.D. PIPE
BOTTOM, /S,DE
0.5
1.0
SENSOR ON SIDE OF
2" PIPE WITH WEDGE
SENSOR ON SIDE OF
l"PIPE WITH WEDGE
I.D.PIPE JTOP
1 BOTTOM
SIDE
_L
_L
1.5 2.0 2.5
MEAN VELOCITY (FT/SEC)
3.0
3.5
4.0
Figure 15. Thermal Wave Velocity Versus Mean Velocity
for all Configurations.
-------
1. Due to the flush mounting of the sensor block, the sensitivity of the
thermal wave propagation velocity to the average velocity in the pipe is
very low (0. 0005 in 1-inch pipe and 0. 035 in 2-inch pipe).
2. The experimental data collected with the present model test
configuration in the 1-inch pipe would not be satisfactory for measuring
fluid velocity if similar results were to be obtained in the full scale
system. This is due to the low sensitivity and the scatter in the data
points. It appears that when the sensor is flush mounted, there is a
limiting value of the thermal wave propagation velocity as the average
velocity in the pipe is increased. This is believed to be caused by the
steepness of the velocity profile at the wall caused by the viscous
friction. Another problem of the data taken thus far is the amount of
scatter in the thermal wave propagation velocity for a constant average
velocity., The variation is believed to be caused by the inherent stretching
and contracting of the wave as it moves down the pipe and thermal noise.
Discrete measurements, therefore, would indicate considerable scatter.
3. It is postulated that the change in sensitivity between the 1-inch I. D.
pipe and 2-inch I. D= pipe was due to variance in the relative placement
of the sensor block in the pipe. This is believed to be true because of
the steepness of the velocity profile near the wall and the non-consistent
effects caused by using the flow wedge.
Although the test model data results are not encouraging from the aspect
of sensitivity and scatter, they do validate the concept of using this
technique to measure flow velocity in water „ Other investigators
(66) are developing a similar technique to be used in air with
a great deal of success. They also have concluded that it is not affected
by contamination and has no moving parts. The application of the
technique in water has problems which are coming to light as a result
of the past experiments, but, it is believed that with further develop-
ment these deficiencies can be corrected.
43
-------
SECTION VIE
DETAILED PROTOTYPE DESIGN
The experimental model test data showed that improvement would
have to be realized in the full scale configuration in terms of sensi-
tivity and scatter. The problem of increasing sensitivity is best
solved by generating the heat in faster fluid streamlines, in order
that the thermal wave velocity is more responsive to changes in the
average flow velocity. This can be achieved by using a sensor block
that is configured as shown in Figure 16. Mounting the heater and
sensor on the upstream side of the arc where the fluid streamlines
are compressed means that the local flow must speed up in order to
pass the volume of fluid that is flowing between adjacent streamlines.
The protrusion into the flow is small, 0. 5-inch, but should signifi-
cantly increase the sensitivity of the measurement. The problem of
scatter is caused by the turbulent nature of the flow and noise that is
superimposed on the response signal. A correlation of the input
heater signal to the thermistor response signal is proposed to pro-
vide a moving average type reading of the thermal velocity and there-
fore reduce the effect of any discrete flow velocity measurement.
The measuring system will utilize five thermal sensor blocks
mounted at 30 intervals as shown in Figure 17. The detailed instal-
lation is depicted on HRC Drawing No. 71320002. The sensor block
(HRC Drawing No. 71320003) is composed of an anodized aluminum
block whose exposed surface has a 6-inch radial arc with a 5-inch
chord length, and is fastened to the sewer pipe. The protrusion into
the flow from the pipe wall is 0. 5 inches. The temperature compen-
sating thermistors, heater strip, and thermal wave sensing
thermistors are flush mounted on the upstream side of the arc.
This configuration should provide greater sensitivity because of
45
-------
FLUID
VELOCITY
CD
SEWER
WALL
SEWER LONGITUDINAL CENTERLINE
TEMPERATURE COMPENSATION
THERMISTOR
HEATER
SENSING THERMISTOR
5.0'
SEWER RADIUS
\ - - - - -
Figure 16. Full Scale Sensor Block in Cross-Section
-------
ELECTRONIC CABLING
TO POWER AND RECORDING
ELECTRONICS
SEWER PIPE
DIAMETER = 2'
OR GREATER
SENSOR
BLOCKS
SEMI-CIRCULAR -
STAGE MEASURING
STRIP
FLOW VELO
SEMI-CIRCULAR
MEASURING STRIP
BOTTOM
Figure 17. Proposed Sewer Pipe Installation of Flow Measurement System
-------
the compression of the fluid streamlines as the flow passes over the
sensor block. The sensor blocks are approximately 1-3/4-
inches wide and are interconnected by a flexible epoxy strip of
the same geometrical cross section. The epoxy strip serves as
the electrical conduit for the sensor power and response signals and
is also required for forming the strip to the inside shape of the pipe.
Manufacturing of the strip assembly entails making a mold of the
proper cross sectional shape and length. Each sensor block will
be pre-assembled, wired and placed in the mold, and then the
epoxy compound will be poured into the mold and allowed to cure.
The final assembly will thus be one integral composite strip with
the sensor blocks molded in place. The sensor blocks, themselves,
can economically be made from 12-inch schedule 40 pipe segments.
The height measuring system utilizes an electronic liquid level gauge
which is manufactured by Marsh and McBurney, Inc. The liquid level
gauge consists of two solid rods, formed to fit the inside curvature
of the sewer pipe. One rod is driven by an electrical signal, and
the other rod acts as a variable tap, whose output varies as a func-
tion of water level. The sensor portion of the instrument, normally
a linear device when used as a straight probe, provides a non-linear
output when curved to fit the conduit. This non-linearity is
corrected by the data processing to be employed. The overall instru-
ment is capable of accuracies better than 1% of full scale. The
installation layout in the sewer pipe is depicted in HRC Drawing
No. 71320004. The rods are imbedded in a faired strip similar to
that used for the flow velocity sensor strip and fastened to the inside
periphery of the pipe. All electrical leads are brought out of the
strips at the top and conduited to the location of the recording and
power electronics which will be located either in a man-hole space
48
-------
in an instrumentation shack adjacent to a manhole access. The
sensors employed to monitor the heat pulse are thermistors that
have been installed in the transducer block previously discussed.
Thermistors rather than the hot film probes are employed because
of their glass coating (longer life) and lower cost. The size of the
thermistors selected provides a small enough time constant to
enable the unit to respond to the 0. 5 Hertz heat pulse rate. The
thermistors have been electrically connected in series with an
equal number placed geometrically parallel and upstream from the
heater element for temperature compensation. By connecting the
sensors in series, a sensing bar is formed which is parallel to the
heating element. The bridge amplifiers employed are of the servo
type with the temperature compensating elements enabling the
sensitivity to remain independent of the liquid temperature. The
signals are connected from the bridge amplifiers to the correlator
circuits via the automatic gain control amplifiers. These ampli-
fiers provide a constant signal to the correlators while the input
signals vary over a range of a hundred to one.
The correlator circuitry employed is one which has recently been
developed around the multiplying electronic elements now available.
This circuitry is expected to produce signals which, over a period of
60 seconds, will produce a signal which is ten to one hundred times
the level of the background noise. The signal fed to the heater
element is an offset square-wave at a rate of 0. 5 Hertz. The sensors
produce a half sine pulse whose peak is delayed in time by the interval
required for the thermal pulse to travel the pre-set distance between
the heater element and the sensor bar. At the sensor bar, the signal
noise is a result of the water turbulence plus the stretching and con-
tracting of the thermal wave. The correlator provides an average of
49
-------
these random events resulting in their self-cancellation. The
shortest path thermal wave, however, is repetitious and therefore
reinforces itself. The outputs of the correlators, which serve as
long term averagers, are fed to voltage controlled phase shifters.
These devices provide for scale expansion of the output signals. The
signals are then sent to a period counter for display and digitizing.
A multiplexer is then employed to sequentially monitor the sensor
outputs and the stage height. The digitized outputs are stored on a
digital cassette recorder along with the time of day of the measure-
ment. The digital cassette recorder provides for the maximum
accuracy while employing a logic scheme enabling more data to be
acquired while the sewer flow is rising than at times of minimal flow.
The stage of flow measurement is also recorded by digitizing the
height gauge signal.
By recording the signals in this manner, the maximum flexibility in
data processing can be obtained. Chart recordings or deviation
measurements of the data can be obtained from any data processing
center. Other methods of recording the data, remote monitoring or
chart recordings can be employed as desired. The details of the
circuitry employed can be obtained from the design drawing package
supplied with this report. The electrical circuits can be traced by
reviewing Drawing No. 71320010 entitled, "Block Diagram Flow
Measuring System".
50
-------
SECTION IX
PRELIMINARY FLOWMETER CALIBRATION
Prior to the insertion of the flowmeter into a sewer for data collec-
tion, a calibration of the unit was accomplished. In order to attempt
a calibration on a meter such as this, designed to monitor the flow
velocity in the boundary layer region of both open and pressurized
flow, it becomes necessary to deviate from a simple primary
standard insertion test. No sewer test channels were identified
having high volume flow capability and accurate flow monitoring.
A test to determine the flow characteristics of the sensor and the
accuracy and repeatability of the'electronic measurement instrument-
ation was then undertaken. A large volume water tank with an
extremely accurate flow rate and wide dynamic range was identified
at the Naval Research and Development Center at Carderock,
Maryland. A contract was arranged with this facility for the use of
a carriage in an 1800-foot towing channel for one day. Accuracy of
the towing carriage was identified to be at least 0. 02 foot/second.
Rigging to enable the quick insertion of a towing strut was also found
to be available. It was therefore decided to attempt to configure the
sensor as a member of a towing strut. The perils of this decision
were identified as being the different type boundary layer configur-
ations which were likely to be encountered when the sensor block
was removed from the concrete wall surface of the sewer pipe. An
examination of the hydraulic design parameters indicated that quick
data checks would be required to ensure the expected turbulent
boundary layer configuration exists over the one to ten feet/second
flow range.
Since the instrument presently employs a long term averaging
device to smooth its readings, it was also determined that the full
51
-------
range of flows could not be investigated due to the limited time that
a constant flow can be maintained. A range of 4 to 5 feet/second
was identified as the limit to obtain readings from the calibration
test.
Even with the limitation described previously, it was decided
that a full scale test of limited range would provide more
working knowledge than a scaled one with full dynamic range;
so, the tests were conducted. The calibration data are summa-
rized in Figure 18. To acquire the curve as shown on Figure 18,
it was necessary to utilize a sand strip one-half inch wide
taped to the leading edge of the strut in front of the sensor block.
This mechanism causes the laminar flow of the strut to be turbulent
at even the low flow speeds and thus avoids the transitional flow
encountered in the one to two feet/second flow ranges as determined
without the sand strip. The time required for equipment set up and
making initial data runs to determine the presence of fully developed
turbulent flow for all data flow rates resulted in the inability to
obtain summary data points, as were desired, due to the limited
total time available.
The plan was to first acquire data on the re-calibrated sensor/
electronic unit, and then to gather data at flow rates under one foot
per second on the other unit. However, sufficient time was not
available to allow the second data set to be obtained.
Checks after the day of calibration revealed proper operation of the
second sensor's electronics, but a combination of two dynamic adjust-
ments was required to affect a change in the range, and the necessary
test equipment was not available at the test site. The sensor electron-
ics used to acquire the data were re-calibrated the day after the
test, and the results are presented in Table 1 and Figure 19.
52
-------
Table 1. Instrument Electrical Calibration
1
Input Signal
Phase Shift
(m sec)
502
527
556
584
612
645
661
684
2
Delay Correction
for Heater Output
-400 m sec
102
127
156
184
212
245
261
284
3
Flowmeter Output
Reading
(m sec)
65
116
190
276
361
511
591
716
Columns 2 and 3 have been curve fitted by a least squares method
and the following equation determined:
1 433
Thermal Pulse - 16.4
fmeter read
(m sec)
\
An index of determination of 0. 998 was obtained for this data.
53
-------
o
0)
CO
rt
O
4.5.
4.0
3.54-
3.0
o 2. 5
S> 2.0
oJ
1.5. -
1.0 . .
0.5
i I i t
200
300 400 500 600 TO 800 9001030
Flowmeter Readout (m sec)
The above curve is fitted by a least squares method and provides the
following equation:
1077
Flowmeter Readout =
Average Flow Velocity
(ft/sec)
- 154.6
Figure IB, Calibration Data
54
-------
o
CD
cc
§
a;
Q
d
bn
•i-i
ra
400
300 • -
250
200
150 +
100 - -
-t-
100
4-
H-
600
700
200 300 400 500
Flowmeter Readout (m sec) (X axis)
Data obtained from Number 2 phase shifter using counter readout.
Electrical insert signal calibration provides the following equation:
y = 16.4 .X°-433
y, and X are axis as indicated.
Figure 19. Electrical Calibration Data
55
-------
It should be noted that the phase shift data were provided by
electronic test instrumentation as an insert calibration.
Data containing a two-step settling time was observed during the
data gathering. The second step of the data provided a regular and
repeatable calibration curve which had been predicted. The second
step response in the settling time however was not anticipated and had
not been revealed by any of the electronic calibrations. Therefore,
it is concluded that the thermal plume must be undergoing a transi-
tion at some point in the steady flow conditions. At the present time
this mechanism is not clearly understood, but it is felt that it could
possibly be attributed to the special strut used in the calibration but
which would not be found in a sewer installation.
In order to better understand this phenomenon and also to gather
data on the uniformity of the ratio of measured flow velocity to
average free stream velocity for different sensor blocks, it is recom-
mended that a pre-demonstration test be conducted under controlled
conditions. This will also provide a true calibration of the entire
flowmeter. The conformance of the data to a smooth and predictable
curve shape is very encouraging. The variation in the plume delay
from the calculated values indicates that the streamlined shape of
the sensor block is enabling the heat plume to penetrate further
into the flow stream than had been anticipated. This would indi-
cate an improvement over the performance previously anticipated
by this measurement technique. The calibration curves were
obtained by performing a least squares fit to the data points. An
index of determination of better than 0. 99 was obtained for each of
the curves. Data points for the meter readout calibration were
selected from the total data required on the basis of on site observa-
tions regarding the validity of each data point. The curves as shown
56
-------
appear to be valid; however, more detailed data are required before
it can be stated with complete certainty that this unit is calibrated
and can acquire data in a sewer flow.
57
-------
SECTION X
FULL SCALE TEST SITE SELECTION
The discussions which HCI has had with area sanitary commissions have
revealed many suitable installation sites. The parties contacted requested
the submission of approved design and fabrication drawings prior to the
finalization of the site. Agreement as to the facilities required centered
about a sewer with a large dynamic flow rate and easily accessible man-
holes. The addition of a small instrument shack next to the sewer
installation is considered a requirement in order that a protective enclosure
for the instruments and electrical power could be provided.
A review of the available test sites revealed many operational difficulties;
however, the selected test site has more advantageous features than any
other site reviewed.
The selected test site is located in Fairfax County, Virginia, along the
Scott's Run watershed just off Georgetown Pike (Route 193), about one-
half mile north of the Interstate 495 interchange. The manhole access
is in a park area approximately 200 yards from Route 193. The sewer
line is 24-inches in diameter and has a flow variation from 0. 6 to 2. 2
million gallons per day. The sewer is a sanitary line; however, infil-
tration during heavy rains is evident.
The main advantage of this site is its close proximity to a meter vault
containing a 9-inch Parshall flume which has been recently calibrated
and is constantly monitored. It is planned to install the HCI flowmeter
50 feet downstream from the meter vault where access through a shallow
manhole is available. Cabling can be run through the pipe to the meter
vault where the instrumentation could be securely located. Power is
already available at the meter vault which is enclosed by a barbed-wire
fence. The site is also far enough from residential connections that
blockage of the pipe can easily be made without fear of flooding base-
ments, etc.
59
-------
The main disadvantage of the proposed site is the lack of dynamic
flow range. Table 2 summarizes the hydraulic characteristics of
the proposed sewer line based on: 1) flow data from the existing
Parshall flume; 2) a recorded pipe slope of 1. 4%; and 3) a
Manning friction factor of 0. 013. Table 2 shows that the expected
range in flow velocity is from 3. 36 to 4. 86 feet per second. The
flow stage range is from 3. 48 inches to 6. 75 inches. Visual in-
spection during peak flow conditions indicate stage height of about
12 inches.
The proposed site is under the jurisdiction of the Fairfax County
Division of Sanitation who has been most cooperative in helping
HCI locate a suitable site. Other sites having more dynamic flow
conditions have been inspected; however, it is proposed that the
first installation be made at Scott's Run where a calibrated
standard is available. If the flow measurement system proves
to be successful at this site, then a second installation could be
made in a more dynamic sewer line.
Blueprints of the proposed site are available for inspection at HCI.
The sewer line empties into the Potomac interceptor line on the
Maryland side of the Potomac River.
60
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Table 2. Scott's Run Hydraulic Characteristics
Scott's Run Hydraulic Data --
Pipe Diameter = 24 inches
Pipe Slope = 0. 014
Minimum Flow = 0. 6 million gallons/day
6 ' y Data for Oct. 1971
Maximum Flow = 2.2 million gallons/day
Assumption for Manning = 0. 013
Roughness Coefficient
Full Pipe Flow Characteristics --
Flow Capacity = 18 million gallons/day
Flow Velocity = 8.4 ft/sec
Open Channel Characteristics--
A. Minimum Flow
1 • Q/Qf = 0. 6/18 = . 0333
2. d/D = .145 or stage = 3.48 inches
3. V/Vf = 0.4 or V= 3.36 ft/sec
B. Maximum Flow
1. Q/Qf = 2.2/18 = .122
2. d/D = 0. 281 stage = 6. 75 inches
3. V/Vf - 0. 578 V = 4. 86 ft/sec
61
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SECTION XI
FULL SCALE FLOWMETER CALIBRATION
Since the previous calibration of the strut mounted sensor blocks
had left many unanswered questions, it was determined that an
additional calibration was required. The Fluids Laboratory at
the National Bureau of Standards was selected as the test facility.
A 16-inch pipe was the flow channel to be employed. The belt
assembly to be installed in the sewer site was modified and in-
stalled within a pipe section. In addition, the strut was mounted
as a center chord of the pipe downstream from the belt sensors.
The details of the test plan and the data gathered are delineated
in Appendix D. In addition, a new insert electrical calibration
was accomplished. The electrical calibration data is presented
in Appendix D.
A review of the data gathered has produced some insight to the
operation of the unit and its various components. A calibration
curve relating unit readout to the average stream velocity has not
been included. The reason for this omission is that the amount of
variation in the data results in a lack of precision of the measured
water velocity. The instrument readout variation was traced and
analyzed after the calibration. The first property of the belt to
cause concern was the extremely low signal levels present at high
water velocities. A logarithmic variation in the peak-to-peak strength
at the sensor bridge was observed. A value approximating
2X10"6°C peak-to-peak was observed during a 14 feet/second
precalibration test. The observed velocity data exhibited a wide
variation of flow velocity in the region of the measurement. These
63
-------
observations imply that under steady flow boundary layer veloci-
ties exhibit variations which do not revolve about a constant value
as previously postulated, but rather have an even distribution
over a range in values. The unit as constructed was able to
handle the extremely low temperature signals, but the manner
of the boundary layer velocity changes do not enable the correlator
circuitry to achieve a unique answer.
The instrument as configured does provide an indication of flow.
If the sensor belt portion of the unit were installed in a situation
in which the boundary layer of the flow was stabilized, then a
repetitive indication of the flow could be attained. Additional
investigations into the mechanisms controlling the flow over the
heater to sensor region of flow would be required if this approach
to fluid flow is to be pursued.
64
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SECTION XII
ACKNOWLEDGMENTS
Mr. George Kirkpatrick of the Environmental Protection Agency for
his technical guidance and sponsorship.
Dr. H. R. Thacker, the Environmental Protection .Agency, who
served as the technical project officer, for his cooperation and tech-
nical guidance.
Mr. Harry Torno of the Environmental Protection Agency for his
technical guidance.
The cooperation of Dr. John Geremia from the United States Naval
Academy, Mr. Ronald Humphrey from DISA Electronics, and
Drs. John Olin and Leroy Fingerson from Thermo-Systems, Inc.
in providing technical information relating to the hot-film anemometry.
65
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SECTION XIII
'REFERENCES
VENDOR LITERATURE
1. DISA Information No. 2 - July 1965, Issued by DISA Elektronik
A/S, Herlev, Denmark.
1-A. The Hot-Wire Anemometer at Low Air Velocities.
1-B. The Air Jet Hot-Wire Microphone.
1-C. Stresses and Deformations in Hot-Wire Probes
1-D. Micromanipulative Apparatus for Delicate Hot-Wire
Probe Repair
1-E. Flush-Mounted Probes.
1-F. A Capacitance - Type Transducer for Absolute Measurements
of Displacements.
2. DISA Information No. 4 - December 1966, Issued by DISA
Elektronik A/S, Herlev, Denmark,
2-A. Time Resolution Power in Correlation Measurements with
DISA Type 66A01 Hot-Wire and Hot-Film Anemometers.
2-B. Measurement of Amplitude and Phase Characteristics.
2-C. Application of Modulated Electromagnetic Waves for
Measurement of the Frequency Response of Heat- Transfer
Transducers.
2-D. Measuring Gas-Dynamic Parameters.
2-E. Pulsating Oil Burners.
67
-------
3. DISA Information No. 5 - June 1967, Issued by DISA Elektronik
A/S, Herlev, Denmark.
3-A. The Hyperbolic Response of Capacitive Transducers, and
Linearizing by Means of an Electronic Circuit.
3-B. Hot-Wire Anemometer Calibration at High Subsonic Speeds.
3-C. The Air Bubble Problem in Water Flow Hot-Film
Anemometry.
4. DISA Information No. 6 - February 1968, Issued by DISA
Elektronik A/S, Herlev, Denmark.
4-A. Low Frequency Characteristics of Hot-Film Anemometers.
4-B. The Shock Front Curvature in a Shock Tube Measured with
Hot-Wire Anemometers.
5, DISA Information No. 7 - January 1969, Issued by DISA Elektronik
A/S, Herlev, Denmark.
5-A. The Measurement of Turbulent Velocity Fluctuations and
Turbulent Temperature Fluctuations in the Supercritical
Region by a Hot-Wire Anemometer and a "Cole" Wire
Resistance Thermometer.
5>-B. On Some Measurements Made by Means of a Hot Wire in a
Turbulent Flow Near a Wall.
5-C. Effect of Wire Mounting System on Hot-Wire Probe Char-
acteristics.
5-D. Pressure Transducers in Liquid-Filled Pressure Systems.
68
-------
6. DISA Information No. 8 - July 1969, Issued by DISA Elektronik
A/S, Herlev, Denmark.
6-A. The X Hot-Wire Probe in a Plane Flow Field.
6-B. Measurement of Air Movements in Internal Combustion
Engine Cylinders.
6-C. Some Problems Concerning the Analytical Evaluation of the
Characteristics of Hot-Wires Immersed in a Fluid of Variable
Pressures and Temperatures.
6-D. Equipment for Traversing Anemometer Probes.
7. DISA Information No. 9 - February 1970, Issued by DISA Elektronik
A/S, Herlev, Denmark.
7-A. Calibration of Probes for Flow Velocity Measurements in
Liquids, in the Range 2-5 m/sec.
7-B. Calibration of a DISA Hot-Wire Anemometer and Measure-
ments in a Circular Channel for Confirmation of the
Calibration.
7-C. Error Due to Thermal Conduction Between the Sensing
Wire and its Supports when Measuring Temperatures With
a Wire Anemometer Used as a Resistance Thermometer.
7-D. Magnetohydrodynamic Effects on Hot-Film Measurements
in Mercury.
7-E. New Trends in Hot-Film Probe Manufacturing.
69
-------
8. DISA Information No. 10, October 1970, Issued by DISA Elektronik
A/S, Herlev, Denmark.
8-A. Karman Vortices in Flows of Solutions of Friction-Drag-
Reducing Polymers.
8-B. Amplitude Probability Analysis of Nonstationary Signals.
8-C,. A Survey of Methods for Measuring Correlation Functions.
8-D. Comparison of Some Methods of Calibrating Hot-Film Probes
in Water.
8-E. A contribution to the Calibration of Hot-Wire Dual Probes.
8-F. A Suitable Method for Calibration of Hot-Film Probes.
9. "Hot Wire and Hot-Film Anemometry; An Introduction to the Theory
and Application of the DISA Constant-Temperature Anemometer" by
C. G. Rasmussen and B. B. Madsen published by DISA Elektronik
A/S, Herlev, Denmark.
10. DISA Scientific Research Equipment, Leaflet No. 2001, June 1970,
Published by DISA Elektronik A/S, Herlev, Denmark.
11. DISA Probe Manual, Leaflet No. 2004, February 1970, Published
by DISA Elektronik A/S, Herlev, Denmark.
12. DISA Transducer Manual, Reg. No. 9150A3211, February 1969,
Published by DISA Elektronik A/S, Herlev, Denmark.
13. Hot Film and Hot-Wire Anemometry Theory and Application
Bulletin TBS, Published by Thermo-Systems, Inc. , Saint Paul,
Minnesota.
14. Design Considerations for Hot-Film and Hot-Wire Anemometer
Applications in Liquids, Published by Thermo-Systems, Inc. ,
Saint Paul, Minnesota.
70
-------
15. Constant Temperature Anemometry Theory Research Report No. 4,
by Leroy M. Fingerson 11 February 1970, Published by Thermo-
Systems, Inc., Saint Paul, Minnesota.
16. "Flow Instrumentation" Published by Thermo-Systems, Inc.,
Saint Paul, Minnesota.
17. "Heated Sensor Finds Wide Applications in Fluid Flow Measurements
(Gases & Liquids)" Published by CGS/Datametrics, Watertown,
Massachusetts.
18. "Fluid Flow Systems" Published by CGS/Datametrics, Watertown,
Massachusetts.
19. "Probes and Sensors" (Hot-Wire and Hot-Film Anemometry),
Bulletin 15P Published by CGS/Datametrics,
Watertown, Massachusetts.
TECHNICAL REPORTS
20. Bellhouse, B. J. , Schultz, D. L. and Karatzas, N. B., "The
Measurement of Fluctuating Components of Velocity and Skin
Friction with Thin-Film Heated Elements, with Application in
Water, Air and Blood Flows", University of Oxford, Dept. of
Engr. Science Report, Report No. 1003, February 1966.
21. Patterson, G. K., Zakin, J. L., "Hot-Film Anemometry Measure-
ments of Turbulence in Pipe Flow: Organic Solvents", University of
Missouri at Rolla, Department of Chemical Engineering,
December 1966.
22. Dreyer, G. F., "Calibration of Hot-Film Sensors in a Towing Tank
and Application to Quantitative Turbulence Measurements"
U. S. Naval Academy, Annapolis, Maryland, March 1967.
71
-------
23. Hoff, M., "Hot-Film Anemometry Techniques in Liquid Mercury",
Grumman Research Department Memorandum RM-414J, June 1968.
24. Rodrigues, J. M., Patterson, G. K., and Zakin J. L., "Effects of
Probe Geometry on Turbulence Measurements in Liquids Using
Hot-Film Constant Temperature Anemometry", University of
Missouri-Rolla, March 1969.
25. Tanaka, D. H., "An Experimental Investigation of Turbulence at the
Wall of a Pipe", U. S. Naval Academy, Anapolis, Maryland,
June 1969.
26. Geremia, John O., "An Experimental Investigation of Turbulence
Effects at the Solid Boundary Using Flush Mounted Hot Film Sensors",
Engr. Report 70-2, United States Naval Academy, January 7, 1970.
27. Mies, R. W., "The Development of Calibration Techniques for a
Flush Mounted Hot-Film Anemometer in the Study of Turbulent
Boundary Layers", Trident Scholar Report, U. S. Naval Academy,
1967.
28. Lubwieg, H., "Instruments for Measuring the Wall Shearing Stress
of Turbulent Boundary Layers", NACA TM 1284, 1950.
29. Liepmann, H. W., and Skinner, G. T., "Shearing Stress Measure-
ments by Use of a Heated Element", NACA TN 3268, 1954.
30. Runstadler, P. W., Kline S. J., and Reynolds, W. C. , "An Experi-
mental Investigation of the Flow Structure of the Turbulent Boundary
Layer", Stanford University Engineering Report MD-8, June 1963.
31. Kos, V. N., Yu. I. Sitnitskiy, "The Question of Measuring Average
Velocity Rate in Pipes by Means of Point Type Sensors", Edited
Translation by the Foreign Technology Division of the Air Force
Systems Command, AD 700368, 18 September 1969.
72
-------
32. Fabula, A. G., "An Experimental Study of Grid Turbulence in
Dilute High-Polymer Solutions", U. S. Naval Ordnance Test Station,
China Lake, California, Report TP 4225, November 1966.
33. Fingerson, L. M. , Blackshear, P. L., "Heat Flux Probe for Dyna-
mic Measurements in High Temperature Gases", University of
Minnesota Report Min-2-P, May 1961.
JOURNALS
34. King, L. V., "On the Convection of Heat from Small Cylinders in a
Stream of Fluid: Determination of the Convection Constants of
Small Platinum Wires with Applications to Hot-Wire Anemometry",
Phil. Trans. Roy. Soc., London, Ser A, Vol. 214, 1914.
35. Raichlen, F., "Some Turbulence Measurements in Water", Journal
of the Engineering Mechanics Division Proceedings of the American
Society of Civil Engineers, April 1967.
36. Richardson, E. V. , and McQuivey, R. S. , "Measurement of Turbu-
lence in Water", Jornal of the Hydraulics Division, ASCE, Vol. 94,
No. HY2, Proc. Paper 5855, March 1968.
37. Melnik, W. L. , Weshe, J. R., "Advances in Hot Wire Anemometry",
International Symposium on Hot-Wire Anemometry, University of
Maryland, July 1968.
38. Resch, Francois, J., "Hot-Film Turbulence Measurements in
Water Flow", Journal of the Hydraulics Division, Proceedings of
the American Society of Civil Engineers, Vol. 96, No. HY3,
March 1970.
39. Collis, D. C., Williams, M. J., "Two-Dimensional Convection
from Heated Wires at Low Reynolds Numbers", Journal of Fluid
Mech. , Vol. 6, P357, 1959.
73
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40. Wills, J. A. B., "The Correction of Hot-Wire Readings for
Proximity to a Solid Boundary", Journal of Fluid Mechanics, P388,
October 1961.
41. Champagne, F. H., Sleicher, C. A., Wehrmann, O. H., "Turbu-
lence Measurements with Inclined Hot-Wires Part 1: Heat Transfer
Experiments with Inclined Hot Wire" Journal of Fluid Mechanics,
Vol. 28 Part 1, pp 153-175, 1967.
42. Symposium on Measurement in Unsteady Flow Presented at the ASME
Hydraulic Division Conference Held in Worcester, Massachusetts,
1962.
42-A. Interpretation of Data and Response of Probes in
Unsteady Flow.
42-B. Fundamentals of Hot-Wire Anemometry.
42-C. The Constant Temperature Hot Thermistor
Anemometer.
42-D. Stable Operation of Hot-Film Probes in Water.
43. Bakewell, H. P., Lumley, J. L. , "The Viscous Sublayer and
Adjacent Wall Region in Turbulent Pipe Flow", Physics of Fluids,
Vol. 10, No. 9, September 1967.
44. Killen, J. M. , Wetzed, J. M., Almo, J. A., "Turbulence Measure-
ments in Dilute Polymer Flows", Symposium on Turbulence Measure-
ments in Liquids, University of Missouri, Rolla, Missouri, 1969.
45. Towsin, R. L., "Turbulence Detection, Results from the Use of
an Unobstructive Technique During Ship Model Testing", Trans.,
INA, 1959.
74
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46. Burns, J. A., Murphy, P. J., "A Hot-Film Anemometer Evalua-
tion of Turbulence Stimulators", International Ship Building Progress,
Vol. 12, April 1965, pp 155-169.
47. Healy, Gerald D., Jr., "Flow Measurement Techniques",
Instruments and Control Systems, March 1965, p 111.
48. Benson, James M., Baker, William C, Easter, Edmone, "Thermal
Mass Flowmeter", Instruments and Control Systems, February
1970, p 85.
49. Laub, John H., "Thermal Flowmeters", Control Engineering,
April 1966.
50. "Paints and Protective Coatings for Wastewater Treatment
Facilities", Water Pollution Control Federation Manual of Practice
No. 17, 1969.
51. "Sewage Treatment Plant Design", Water Pollution Control
Federation Manual of Practice No. 8, 1967.
52. "Operation of Wastewater Treatment Plants", Water Pollution
Control Federation Manual of Practice No. 11, 1970.
THESIS
53. Patterson, G. P., "Turbulence Measurements in Polymer Solutions
Using Hot Film Anemometry", PhD Dissertation, University of
Missouri, Rolla, Missouri, 1966.
54. Hubbard, P. G., "Constant-Temperature Hot-Wire Anemometry
with Application to Measurements in Water". Dept. of Mechanics
and Hydraulics, Graduate College of the State University of Iowa,
June 1954.
55. Ling, S, C., "Measurement of Flow Characteristics by the Hot-
Film Technique", Department of Mechanics and Hydraulics,
Graduate College of the State University of Iowa, June 1955.
75
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56. Dell Osso, L., "Turbulence Measurements in Water in an Open
Channel with the Hot-Film Anemometer", Dept. of Chem. Engr.,
Graduate College of Rice University, May 1966.
57. McQuivey, R. S., "Dissertation Turbulence in a Hydrodynamically
Rough and Smooth Open Channel Flow", Colorado State University,
August 1967.
TEXTBOOKS
58. Chow, Yen Te, "Open-Channel Hydraulics", McGraw Hill, 1959.
59. King, Horace Williams and Brater, Ernest F., "Handbook of
Hydraulics" McGraw-Hill, Fifth Edition, 1963.
60. "Design and Construction of Sanitary and Storm Sewers", WPCF
Manual of Practice No. 9, Published by Water Pollution Control
Federation, October 12, 1967.
61. Hinze, J. O., "Turbulence", McGraw-Hill, 1959.
62. Streeter, Victor, L., "Handbook of Fluid Dynamics", McGraw-
Hill, 1961.
63. Robertson, James M. , "Hydrodynamics In Theory and Application",
Prentice Hall, 1965.
64. Kreith, Frank, "Principles of Heat Transfer", International Text-
book Company, 1958.
65. Giedt, Warren H., "Principles of Engineering Heat Transfer",
D. VanNostrand, 1957.
75
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PAPERS
66. Paper No. 2-5-71 Presented at the Symposium on Flow Its
Measurement and Control in Science and Industry Pittsburgh, Pa.
May 10-14, 1971 "Quasi-Correlation Circuit for Thermal Pulse
Time-of-Flight Flowmeter" by Ronald D. Hill and
Richard D. McGunigle.
77
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SECTION XIV
APPENDICES
Page No.
A L,ist of Vendors 81
B Drawing List 83
C Strut Flowmeter Test at NSRDC 85
Table 1: Flowmeter Electrical Calibration 89
Table 2: Flowmeter Calibration 90
D Flowmeter Test at NBS
Table 1: N. B. S. Calibration Data 97
79
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SECTION XIV
APPENDtX A
LIST OF VENDORS
1 Alnor Instrument Co.
Div. 111. Testing Labs
151 W. Hubbard St.
Chicago 10, 111.
2 Bacharach Indicator Instr. Co.
200 North Bradock Ave.
Pittsburg 8, Penn.
3 Beckman & Whittley Inc.
973 E. San Carlos Ave.
San Carlos, California
4 Davis Instr. Mfg. Co.
709 E. 36th
Baltimore 18, Md.
5 F. W. Dwyer Mfg. Co.
P. O. Box 373V
Michigan City, Indiana
6 Electric Speed Indicator Co.
12234 Triskett Rd.
Cleveland 11, Ohio
7 Fisher Scientific Co.
244 Fisher Bldg.
Pittsburg 19, Penn.
8 Flow Corp.
205 6th St.
Cambridge 42, Mass.
9 Friez Instruments
Div. Benix Corp.
1400 Taylor Ave.
Baltimore 4, Md.
10 Henry J. Green Instr. Co*
2500 Shames Drive
Besberry, N. Y.
11 W. & L. E. Gurley
Union Street
Troy, N. Y.
12 Hasting Raydist, Inc.
Newcomb Ave.
Hampton, Virginia
13 Hill & Co.
E. Vernon
P. O. Box 189
Lake Geneva, Wise.
14
15
16
18
Clark H. Joy Co.
27005 Knickerbocker Rd.
Bay Village 40, Ohio
Kenyon Inst. Co.
P. O. Box 355
Brewster, N. Y.
Inc.
Koeffel & Esser
300 Adams
Hoboken, N. J. 07030
M. E. D. Indicators
Div. United Instr. Labs
104 W. Jefferson St.
Falls Church, Va. 22046
Science Assoc.
194 Nassau St.
Box 216
Princeton, N. J.
19 Taylor Inst. Co.
Amest St.
Rochester, N. Y.
20 Thermo Systems, Inc.
2418 E. Hennepin Ave.
Minneapolis 13, Minn.
81
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LIST OF VENDORS (Cont'd)
21 Universal Instr. Co.
3807 Bunker Hill Rd.
Brentwood, Md.
22 Westberry Mfg. Co.
3400 Westach Way
Sonoma, California 95476
23 Wilson Products
Div. Electric Storage Battery Co.
2nd & Washington St.
Reading, Penn.
24 Baily Meter Co.
1033 Ivenhough Rd.
Cleveland 10, Ohio
25 Barton Instr. Co.
580 Monterey Pass Rd.
Monterey Park, Cal.
26 Bristel Co.
P.O. Box 1790 MBB
Waterberry 20, Conn.
27 Brook Instr. Co., Inc.
407 West Bend St.
P.O. Box MRB 9698
Hatfield, Penn.
28 F. W. Briar Mfg. Co.
P.O. 373Z
Michigan City, Indiana
29 DISA Electronics
779 Susquehanna Ave.
Franklin Lakes, N.J.
#891-9460
82
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E-71320002
C-71320003
A-71320008
B-71320013
C-71320015
E-71320017
E-71320018
C-71320019
C-71320020
C-71320021
C-71320022
C-71320023
C-71320024
C-71320025
B-71320026
B-71320027
B-71320028
B-71320029
E-71320030
E-71320031
C-7132Q032
E-71320034
D-71320035
D-71320036
D-71320040
D-71320041
SECTION XIV
APPENDIX B
DRAWING LIST
Flow Sig. Pick-up Ass'y and Installation
Housing, Flow Pick-up
Wiring List
Bridge Preamp
Flowmeter, Sensor Electronics
Instrument Container Ass'y
Panel Ass'y
Door Ass'y Counter Mounting
Latch - Counter Support
PC Card (Height Gauge)
Bottom Cover - Mod.
Top Cover - Mod.
Bracket (Gauge and Time Code Gen. Mount)
Side Card Holder
Bracket
Bracket, Hinge
Bracket, Hinge
Spacer
Case, Power Supply
Instrument Case Modification
Mounting Plate, Power Supply
Power Supply Ass'y
Flow Meter Test Ass'y
Phase Shifting Circuit
Block Diagram, Flow Measuring Device
A/D Converter, Flow Measuring Device
83
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D-71320042
C-71320043
C-71320044
A-71320045
D-1007-01-210
D-1007-10-231
1 00046
SK-FM203
SK-FM204
SK-FM210
SK-FM211
SK-FM212
SK-FM226
SK-FM227
SK-FM228
SK-FM401
SK-FM402
DRAWING LIST (Cont'd)
Logic Diagram, Data Acquisition
Voltage Controlled Phase Shifter
Correlator
Cal. Curve - Height Gauge
Plus and Minus 15 volt power supply (BL Packer)
Plus 5 volt power supply (BL Packer)
Water Level Gauge Model 100
(March & McBurney, Inc.)
Output Multiplexer Schematic
Sequence Control Schematic
Phase Shifter Schematic
Heater Cut-off Schematic
Level and offset Adj. Schematic
Multiplier Test Card Schematic
SIMPLIFIED Block Diagram
Analog Section Schematic
Calibration Pipe Layout
Sewer Belt Details
84
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SECTION XIV
APPENDIX C
STRUT FLOWMETER TEST AT N. S. R. D. C.
PURPOSE
To subject the flowmeter sensor block and electronics to a full scale
preliminary calibration, the sensor is to have a constant velocity
water flow passed by the sensor. Accuracy and repeatability of
the flowmeter is to be determined from these tests.
TEST PLAN
In order to provide a constant flow of water at measured accuracies
of at least one percent, it is proposed to transport the flow sensor
blocks through a still water basin. To accomplish this, a tow
carriage at the NSRDC facility at Carderock, Maryland, is to be
utilized. A strut is to be used as the mounting tool for at least two
sensor blocks. The carriage is to be transported at various veloc-
ities from one to ten feet per second. A comparison of the two
sensor block readings as a function of the sensor block velocity is
to be accomplished. The velocity runs are to consist of ten different
velocities and at least three runs at or near the various velocities
are to be taken to investigate the repeatability of the flow measure-
ments. The number of data points taken will be a function of the
available time of the calibration facility. Prior to these detail data
runs, at least two data runs at the extremes of the velocity range
are to be accomplished to define the range of data available.
The data is to be gathered by monitoring the counter on the carriage
to determine the water velocity, and the flowmeter counter to
determine the sensor reading. The attached data sheet is to be
utilized for the recording of all data.
85
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CALIBRATION DATA RUNS
Sheet (2)
Data Run
6
6
7
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
15
15
16
17
18
19
20
21
22
23
Carriage Speed
(ft/sec)
1.023
1.023
1.25
1.25
1.50
1.50
1.50
1.50
1.71
1.71
2.0
2.0
2.25
2.25
2.50
2.50
2.73
2.73
2.98
2.98
3.24
3.49
3.77
3.50
2.72
2.98
4.00
0.741
Sensor Reading
(m sec)
832
158
832
off scale
end of run
end of run
567
off scale
485.8
off scale
380.5
off scale
323
off scale
315
off scale
303
off scale
296.8
off scale
278
155
142
212
251
254
116
97
Sensor No.
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
2
2
2
2
2
2
1
86
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CALIBRATION DATA RUNS
Sheet (2)
Data Run
24
25
26
27
28
Carriage Speed
(ft/sec)
0.51
2.49
2.98
3.24
1.80
Sensor Reading
(m sec)
581
284
212
173-198
**
Sensor No.
1
2
2
2
2
* Settle to 203 settle to 198 runaway low 173 and persistent; 161 absolute
** Started run at 3.0 ft/sec slow to 1. 75 ft/sec read 398, 403 and 420
at end of the run.
87
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INSTRUMENT CALIBRATION DATA
In order to better understand the measurements obtained from this
flowmeter, it was deemed necessary to calibrate the instrument with
electrical signals. A signal was fed to the unit in lieu of the
thermistor signals and was delayed by a calibrated amount. The
output reading of the flowmeter was recorded for each phase delayed
signal. Table 3 indicates a typical data calibration run.
Column 2 of Table 3 is a correction factor of -400 milliseconds
which is necessary to account for the delays associated with driving
the heater and the sensing offset factor of the thermistor bridge/
preamplifier combination. The -400 milliseconds value is a theoret-
ical number which has been verified in laboratory tests.
Columns 2 and 3 have been fitted by a computer curve program and
the following equation derived:
C\0 433
meter read!
in msec I
The index of determination for this equation with the aforementioned
data is 0. 9986.
The instruments used to acquire this data are a Ling 401AR Servo
Analyzer and a Monsanto 100B counter.
SUMMARY OF TEST
A summary of the results of the flowmeter's calibration is indicated
in Table 4. It should be noted in Table 4 that only a portion of the
total data runs have been selected for analysis. The other test runs
have not been presented for analysis due to questions regarding the
test during the gathering of the other data points. For example,
after some data points had been acquired, it was determined that the
data readout had a persistent reading of one value for a long interval.
-------
Table (1). Flowmeter Electrical Calibration
Input Signal Delay Corrected Delay to Account Flowmeter Output
(m/sec) for Heater Opr. (m sec) (m sec)
502 102 65
527 127 116
556 156 190
584 184 276
612 212 361
645 245 511
661 261 591
684 284 716
89
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Table (2) . N. S. R. D. C. Calibration Test Data
Data Carriage Readout Thermal Wave
Run Speed Counter Actual Flow Thermal Velocity
. ) (ft/sec) (m/sec) Wave Flow Ratio % (ft/sec)
19 1.50 576 10.7 0.161
10 1.71 485 10.4 0.174
11 2.00 380 9.75 0.193
12 2.25 323 9.30 0.209
i? 3.49 155 8.40 0.294
}8 3.77 142 8.12 0.306
22 4.00 116 8.20 0.328
25 2.49 248 9.60 0.238
26 2.98 212 8.56 0.254
27 3.24 181 8.45 0.274
90
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However, with a little more settling time the readout would change to
a new permanent value. After this effect had been noted, the data
runs were repeated to determine the final readout value. The
resultant readout numbers have been analyzed by a least squares data
fit. The resultant equation,provides an Index of Determination value
of 0. 9944, indicating an extremely good curve fitting. The resultant
equation is:
1077
Delay Indicated =?•" -. ^—=^—rr- - 154. 6 -Y4)
(msec) Average Flow Velocity ,V
(ft/sec)
In addition, the data points were plotted on a semilog plot as
indicated in Figure 20. Flow velocity in feet per second is one axis
while the counter readout in milliseconds is indicated on the other
axis. Note that a smooth curve line is formed by the data points.
The curvature of the line at the low carriage speeds is due to the
electronic range of operation. An examination of Table 4 indicates
that the ratio of actual flow to the measured thermal wave flow is
greater than the unit was expected to encounter. This flow rate
caused a change in operating range to be implemented in the field to
reduce the sensing range. Since a limited time was available to
check the realignment, it has been determined after the test that
most of the data has been obtained in the non-linear region of the
electrical calibration. In addition, one sensor did not operate in the
region of 1. 0 feet per second to 10. 0 feet per second, but rather
from 1. 0 feet per second down in velocity. Therefore, the taking of
double data for analysis redundancy was not possible.
After the adjustment to alter the flow velocity measurement region,
there were no further adjustments or malfunctions of the equipment.
An electrical calibration was performed immediately upon the return
91
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s
o
o
0)
w
rH
-------
to the laboratory as stated in the Instrument Calibration paragraph.
The laboratory tests indicate a total hysteresis and stability error
range of less than 1 percent for the electronic measurement system.
The combined hydrodynamic characteristics and thermal wave
measurement characteristics of the sensor block were the real
purpose of this test. A few preliminary data runs indicated the strut
characteristics differed with those found on the wall of a sewer pipe.
To ensure the presence of turbulent flow, a strip of sandpaper was
added to the front of the strut. After this addition, the thermal wave
velocity, which was measured by the sensor, increased an order of
magnitude indicating turbulent flow was present. Measured flow
velocities indicate that the strut configuration in the velocity range
to 5 feet per second presented a different flow regime environment
than was to be found in a sewer pipe. The uniformity of the data
indicates the sensor configuration is workable; however, the range
of percentage of average flow velocity indicates that higher than
expected thermal wave velocities were measured. A review of the
test arrangements, however, provide an explanation of this phe-
nomena and indicates that this test cannot be used as a judgment of
the overall usability of this measurement technique. A different
test technique must be employed to ensure a test which is not only
accurate in its velocity calibrations, but also simulates Reynolds
numbers in pipe flow which are similar to those expected in a
sewer pipe. The flow characteristic change accounts for the require-
ment to alter the electronic sensitivity. It should be noted that
during these full scale tests no problems in sensitivity were noted.
A repeat calibration is recommended with particular attention given
to the hydraulics of the test. If well ordered, repeatable test data
are obtained, as in this test, then the unit can be considered a feasible
93
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flowrneter. The test results obtained also confirm the theories
concerning the penetration of the thermal pulse through the boundary
layers to provide a secondary measurement of the average flow
velocity. The test also indicates that the sensor shape is correct in
that a speed up and thinning of the boundary layers is being accom-
plished.
There is presently no theory at hand to explain the settling of the
data to one readout number than shifting to another. No laboratory
testing has been able to duplicate this condition. More testing will
be required to validate theories explaining this phenomena.
94
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SECTION XIV
APPENDIX D
FLOWMETER TEST AT
NATIONAL BUREAU OF STANDARDS
PURPOSE
To subject the flowmeter sensor blocks, as configured, to measure
flow in a sewer pipe, to a full scale calibration. The sensors are
to have a set of constant water velocity flow conditions which cover
the design range of the flowmeter. Accuracy and repeatability are
to be determined from these tests.
TEST PLAN
A belt containing sensor blocks is to be mounted in a 24-inch pipe
section and the pipe inserted in the National Bureau of Standards
Flow Test Facility. In addition, the test strut containing two
sensor blocks is to be mounted as a center chord across the pipe.
A comparison of the velocity measurements of the belt sensors
and the strut sensors as a function of wat er velocity is to be ac-
complished. The water velocities to be utilized will vary from
1 foot/second to 14 feet/second with a five-step calibration pro-
gressing with increasing velocity from 1 to 14 feet/second and then
decreasing from 14 to 1 feet/second. At each velocity five data
runs are to be gathered with a primary calibration to be accom-
plished by measuring the quantity of water over a specified in-
terval. Four of the data runs will be on the belt sensors and one
devoted to the strut sensors. All data is to be gathered by the
automatic data recordings of the flowmeter and by manually mon-
itoring a parallel readout device.
95
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The nominal velocities to be investigated and their order of in-
vestigation are to be as follows: (1, 3; 7, 10; 14) feet/second.
If this data appears useful, then (12, 9, 6, 4, 2) feet/second are
to be investigated.
The following data are presented as the most significant of that
gathered and represents a compilation of the total numbers
obtained.
96
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Run
No.
N. B. S.
Measured
Velocity
Table 1
N. B. S. Calibration Test Data
Sensor Sensor Sensor Sensor Sensor Sensor
#1 #1 #1 #2 #2 #2
Read "C Meas. Read °C Meas.
Out Peak to Velocity Out Peak to Velocity
ffjj \ V7U.U JTCCtn. tU V CiU^iiy WUt JTCO.JV LU V ClU^lt-'
(tt/sec) (msec) Peak (ft/sec) (msec) Peak (ft/sec)
1.401
2.595
8
4.100
393
546
497
386
715
697
785
770
778
811
957
003
0015
0012
2.134
10
1.857
493
509
555
581
617
452
571
526
435
434
002
003
.0454
.0483
.0475
.0453
.0528
.0523
.0556
.0540
.0542
.0550
saturated
reading
.0474
.0477
.0485
.0490
.0499
.0467
.0488
.0478
.0458
.0460
535
534
515
509
504
772
777
775
780
777
829
825
821
821
817
761
743
702
658
636
678
525
561
635
627
009
007
006
008
009
.0432
.0432
.0420
.0419
.0419
.0461
.0463
.0458
.0459
.0458
saturated
reading
.0459
.0457
.0447
.0441
.0438
.0447
.0426
.0427
.0438
.0437
97
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TEST DESCRIPTION
The data obtained by this test is indicated in Table 5. The data
shown has been selected and is the best of the test runs. In ad-
dition to the average stream velocity, as determined by the
National Bureau of Standards, the sensor readouts are listed,
as well as the approximate temperature variation at the sensor
bridge, and the calculated local stream velocities at the sensor
blocks. The local sensor velocities were determined from the
Sensor Readout data and the electrical calibration of the instrument
as presented in Figure 21. The data for Figure 21 was obtained as
in the previous calibration test by inserting an electrical signal
at the sensor input to the unit and varying the phase shift while
monitoring the output. All data points were taken after a five-
minute stabilizing interval had elapsed.
TEST SUMMARY
A review of the data indicates a widely varying range of sensor
velocity measurements. In addition, the extremely low signals
indicate that some data jitter is present due to the fact that noise
signals in excess of the data signals were present. A close visual
observation of the wave forms indicated that hydrodynamic phenom-
ena was inducing apparent water velocities at the sensor face that
appeared to vary over a wide range of values with time. No pat-
tern or randomness was determined during these tests but, in
addition, no predominance of a given value was noted in short
term observations. The lack of preponderance of a given flight
time would lead to a varying output number from the processing
electronics in the unit. Indeed this is the indication which was
noted and it is therefore concluded that more investigation into
98
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the water velocity variations expected, in a boundary layer of a
pipe flowing as in this calibration test, is required.
99
-------
noo
1000
Ul
re C
r- O
0> O
Q M—
900
800
yon
300
400 500 600 700
Counter Reading (milliseconds)
800
Figure 21. Electrical Calibration (Actual Time Delay
vs. Reading of the Instrument).
100
"U.S. GOVERNMENT PRINTING OFFICE:1973 514.
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
w
"A Thermal Wave Flowmeter for Measuring Combined Sewer Flows"
Robert A. Blase
Paul W. Eshleman
Hydrospace-Challenger, Inc.
2150 Fields Road
Rockville, Maryland 20850
12. Sponsoring Organist;on Environmental Protection Agency
Environmental Protection Agency report number EPA-R2-73-145
*. Pf-'orntis" Qigar:-ition
A\-,.,.rr Nt.
EPA 11020 EYD
EPA 14-12-911
13 Type: ReiM: -nil
PfT-oa Covered
Contract 10/70-6/72
A study of the application of thermal techniques to the measurement of flow rates
in combined sewers has been conducted. The utilization of flush-mounted hot wire or
hot film anemometers in a direct reading mode was extensively investigated. It was
concluded that such a direct reading application was not feasible due to shifts in
calibration caused by the build-up of contamination and the lack of commercially
available units with sufficient ruggedness and reliability for application in a com-
bined sewer pipe.
A particular technique, which is based upon measuring the time-of-flight of
thermal pulses generated at various positions around the perinphery of the pipe,
was investigated in depth. A full scale prototype unit was fabricated and tested.
These tests indicated that the configuration does not provide signals which have
precision to enable the measure of fluid flow with the desired accuracy.
17a. Descriptors
*Flow Measurement, *Combined Sewers, * Anemometers, *Flowrneters,
Discharge Measurement, Storm Drains, Hydraulics
17b. Identifiers
*Time-of-flight, *non-invasive, correlator, integrated circuit
• 17c. COWKRFipirl& Group Q7 B
18. A:rih<^i!ity 19.
20.
. Ab.-itt actor Paul W. Eshleman
Sfurity C'-iss.
(Report)
Security Class.
(Pvge)
21. $'•:: Ot
Pages
22. Price
Send To:
WATt R PE" L^OU Rr F S S'' 1 ( N
U S DT PA PT V5 ENT OF T H L
WASH IN'. ION L> '' I?O24i
\ Hydrospace-Challenger ,
-|F|. ! NTO'HMATh.iN CENTER
r j T I. K 1 0 R
Inc.
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