tPA 60Q/2-78-049
Mrch '978
Environmental Protection Technology Series
DEVELOPMENT OF AN OPTICAL CONVOLUTION
VELOCIMETER FOR MEASURING STACK FLOW
Environmental Sciences Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development. U S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental 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.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-049
March 1978
DEVELOPMENT OF AN OPTICAL CONVOLUTION VELOCIMETER
FOR MEASURING STACK FLOW
by
M.J. Rudd
Bolt Beranek and Newman Inc.
Cambridge, MA 02138
Project Officer
John Nader
Emissions Measurement and Characterization Division
Environmental Sciences Research Laboratory
Research Triangle Park, NC 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NC 27711
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DISCLAIMER
This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S. Environmental Protection Agency and approved for publication.
Approval does not signify that the contents necessarily reflects the views and
policies of the U.S. Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or recommendations
for use.
ii
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PREFACE
The work reported herein was performed under the auspices of Memorandum
of Agreement (MOA) EPA-1AG-D6-F044, entitled, "Development of the Optical
Convolution Velocimeter." This MOA was between the Air Force Flight Dynamics
Laboratory located at Wright-Patterson Air Force Base, Ohio 45433, and the
Environmental Sciences Research Laboratory of the U.S. Environmental Protect-
ion Agency (EPA) located at Research Triangle Park, North Carolina 27711.
Mr. Gary A. DuBro was the technical monitor for the Air Force, and Mr. John
Nader the technical monitor for the EPA.
This report was prepared by Bolt Beranek and Newman Inc., Cambridge,
Massachusetts 02138, under USAF Contract F33615-76-C-3051. The objective of
this investigation was to design and fabricate a prototype device based on
optical convolution principles for the measurement of gas system velocities
in emission sources and to test its applicability under simulated conditions.
The program at Bolt Beranek and Newman Inc. was performed by Dr. Michael J.
Rudd.
ROBERT F. LOPINA, Col, USAF
Chief, Flight Control Division
Air Force Flight Dynamics Laboratory
iii
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ABSTRACT
A new type of instrument has been developed and tested for the measure-
ment of stack flow velocities. The instrument is optical and generates a
shadowgraph pattern of the wake from a small heater. This shadowgraph is
projected on a mirror grating of precise dimensions and the reflected light
detected by a photodiode. The output of the photodiode fluctuates at a
frequency that is related to the velocity with which the turbulence is
convected across the grating. By measuring this frequency, the flow
velocity is determined.
A version of this optical convolution velocimeter (OCV), as it is
called has been built to withstand a temperature of 200°C and combustion
gases. This unit has been tested in both a wind tunnel and EFA's stationary
source simulation facility (SSSF). The agreement with a pitot tube was close,
1% in the wind tunnel and 2 - 2.5% in the SSSF. Some difficulty in signal
processing was found at high speeds and high temperatures or dust loadings,
but this can be cured.
The OCV promises to be a much more accurate and easier to use instrument
than the pitot tube, at little additional cost.
This report was submitted in fulfillment of interagency agreement
MOA-EPA-IAG-DE-F044 by Air Force Flight Dynamics Laboratory, Dept. of the
Air Force under the partial sponsorship of the U.S. Environmental Protection
Agency. This report covers a period from July 1976 to February 1977 ,
and work was completed as of February 1977 .
iv
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CONTENTS
PREFACE iii
ABSTRACT iv
FIGURES vi
ACKNOWLEDGMENT vii
1. INTRODUCTION 1
2. CONCLUSIONS 3
3. RECOMMENDATIONS 4
4. DESIGN OF THE STACK OCV 5
5. TESTING AND EVALUATION OF THE STACK OCV 10
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FIGURES
Number Page
1 Principle of the Optical Convolution Velocimeter ................ 2
2 OCV Sensor (Drawing) ............................................ 7
3 The Sensor Head of the Stack OCV ................................ 8
4 Close-Up of the Mirror-Grating of the Stack OCV ................. 9
5 Calibration in BBN Wind Tunnel .................................. 11
6 Angle of Incidence Sensitivity .................................. 12
7 Stack OCV Set Up in the Stationary Source Simulation Facility
(SSSF) [[[ 14
8 Run 1 - Warm, 105°C ............................................. 15
9 Run 2 - Humid, 8.0% H20 and 105° C ............................... 16
10 Run 3 - Very Humid, 14.9% H20 and 105°C ......................... 17
11 Run 4 - Ambient, 80°F ........................................... 18
12 Run 5 - Moderate Dust Loading, 100 - 1400 mg/M .................. 19
3
13 Run 6 — Heavy Dust Loading , 6QO - 4000 mg/M ...................... 20
14 Run 7 - Hot, 1500°C .............................................. 21L
15 Run 8 - Combustion Products 4.7% H20 and 150°C .................. 22
16 Run 10 - Very Hot, 200°C ........................................ 23
17 Run 11 - Fine Dust, 20 - 200 mg/M ............................... 2^
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ACKNOWLEDGMENTS
The author wishes to gratefully acknowledge the help and suggestions from
G. Dubro and D. Kim of the Air Force Flight Dynamics Laboratory of the Wright
Aeronautical Laboratories since they were the original inventors of the Optical
Convolution Velocimeter. The author also wishes to acknowledge the aid of
J. Nader of the Stationary Source Emissions Branch, EPA, for the suggestion to
use fiber optics in the stack OCV and for his support during the tests in the
Stationary Source Simulation Facility.
vii
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SECTION 1
INTRODUCTION
THE OPTICAL CONVOLUTION VELOCIMETER (OCV)
The optical convolution velocimeter was conceived by DuBro and Kim* (U.S.
Patent No. 3,953,126) as a noninvasive method for measuring aircraft speed
that eliminates many of the problems encountered with the Pitot-static tubes
currently used on board aircraft.
The OCV uses a light-emitting diode (LED) as its light source. The out-
put of the LED is collimated by the lens, and projected through the turbulence
onto a grating (see Figure 1). The turbulence is generated by the wake of an
object placed in the flow. A mirror behind the grating returns the light
through a lens onto a photodiode. As the light passes through the turbulence,
it is refracted, and a "shadowgraph" pattern of bright and dark bands is
formed on the grating. As the turbulence is convected with the mean flow, the
shadowgraph pattern is convected over the grating. We can describe the light
transmitted by the grating as
/ l(x-y) G(x) dx = F(y)
where I(x-y) is the shadowgraph pattern that is convected in time by distance
y, and G(x) is the grating transfer function. The function F(y) is the con-
volution of the shadowgraph and the grating. By Parseval's theorem, the spec-
trum of this convolution is equivalent to the product of the spectra of I(x)
and G(x). If the spectrum of G(x) is narrow, the spectrum of the convolution
function F(y) is narrow, and it will be sinusoidal with a frequency equal to
that at which the turbulence crosses the grating. Hence, the velocity can be
found by measuring this frequency.
The purpose of this report is to describe the development of the OCV for
making in-stack velocity measurements. The OCV has a number of inherent
advances over the pitot tubes which are currently employed. First, it is an
absolute instrument and never needs recalibration once it has been set up.
Secondly, it is unaffected by ambient conditions such as pressure and tempera-
ture. Thirdly, it just measures one component of the velocity. Fourthly, it
can be given a digital readout very inexpensively: in fact, the whole OCV
concept leads to a very inexpensive instrument. Thus the OCV promises to be a
much more accurate and convenient to use instrument than the pitot tube, at
very little additional cost.
*D. Kim and G. DuBro, 1974, "The Optical Convolution Velocimeter" presented at
the second Project Squid Workshop, Purdue University, Lafayette, IN, March 26-27.
1
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I FLOW
PHOTO-DIODE
LED
TURBULENT
WAKE
MIRROR
Figure 1. Principle of the Optical Convolution Velocimeter.
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SECTION 2
CONCLUSIONS
An optical convolution velocimeter has been built which will success-
fully operate in the hostile environment of a stack. It operated in an
environment of 200°C and 4000 mg/m of dust loading with little difficulty.
The general standard deviation of the differences between the OCV and the
Pitot tube was 1% in the Bolt Beranek and Newman (BBN) wind tunnel and 2 - 2.5%
in the SSSF.
The OCV had demonstrated itself as an accurate and easy to use flow
measuring instrument for use in stacks.
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SECTION 3
RECOMMENDATIONS
As a result of this program, a number of improvements to the OCV are
suggested
1. Incorporate a high pass filter into signal processor. This will
cure the difficulties encountered at high speeds with high temperatures and
dust loadings.
2. Increase velocity range to 45 m/sec. The current unit was designed
for 20 m/sec and with some modifications to the electronics this can be
increased.
3. Combine signal processor and sensor head power supplies.
4. Calibrate against a Laser Doppler Velocimeter (LDV). An LDV is a
more accurate instrument than a pitot tube and it provides a better and more
reliable check on the calibration of the OCV.
One nice point about the operating principle of the OCV is that it is
not restricted to making point measurements in the flow, but can be used to
integrate across the whole stack. Such a system would have a collimated
light source on one side of the stack and the grating and detector on the
other. The development of such an instrument could consist of several stages.
a. Fabricate a cross-stack OCV.
b. Test the cross-stack OCV in the SSSF and investigate whether a mark-
ing heater was still required.
c. A theoretical and experimental investigation of the effects of a
skewed velocity distribution in the stack on the OCV reading. This
will determine whether the OCV can operate in one direction across
the stack or must be used in both directions.
d. Design of a cross-stack OCV for field operation. This would include
such features as an air curtain over the optical windows.
e. Reporting on the above activities.
This would generate a design for an OCV which would be capable of
continuously monitoring the flow in a stack.
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SECTION 4
DESIGN OF THE STACK OCV
At the request of the EPA, BBN has designed a high temperature version of
the OCV which is suitable for insertion into a chimney stack. The main
changes required for the instrument to operate under hot and corrosive condi-
tions were to eliminate semiconductor devices from the hot end of the OCV,
make it long enough to insert in the stack and use corrosion resistant materials.
The main changes were:
1. Replace light emitting diode with a tungsten halogen lamp.
2. Move the photodiode into a cool area and couple it to the head with
fiber optics.
3. A 2 m extension to insert the OCV into the flow.
4. Casing made from stainless steel instead of aluminum.
5. A high temperature grating.
We are greatly indebted to Mr. John Nader, of the EPA, whose suggestion it was
to couple the cool photodiode to the hot region with fiber optics. A drawing
of the OCV is shown in Figure 2 and views in Figures 3 and 4.
The grating was made by first photographically forming a Ronchi grating
and removing the gelatin from the clear areas. The grating was then coated
with vacuum deposited chromium in order to make it reflective. The grating
was then bonded into its holder, chromised side on the back, with a high
temperature silicone rubber.
The hot end of the stack OCV was required to be placed in a 200°C air-
stream. Accordingly, it was designed to withstand about 260°C. The tungsten
halogen lamp likes an envelope temperature of more than 250°C, but the base
temperature must not exceed 350°C. The high temperature stainless steel clad
fiber optics from Dyonics was rated at 320°C (although we later found this to be
optimistic). A Teflon holder for the lamp and fiber optics was employed. A
Teflon washer also held the collimating lens in place.
At the cold end of the stack OCV, the body was made of anodised aluminum.
The electronics was mounted on a circular printed circuit card and rated at
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120°C- A 5-pin electrical connector couples the OCV head with the signal pro-
cessor. The signal processor was the same as that which was used in the pre-
vious program with the U.S. Air Force and is described fully in Technical
Report AFFDL-TR-76-132.* The processor is a special device for which BBN has
applied for a patent and is called a "correlation discriminator." It measures
accurately the frequency of a noisy and widely fluctuating signal.
*Rudd, M.J., "Development of Prototype Optical Convolution Airspeed Sensor,"
Air Force Flight Dynamics Laboratory Report AFFDL-TR-76-132.
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TUNGSTEN HALOGEN
LAMP
rCONNECTOR
MIRROR
GRATING
FIBER OPTIC CABLE
L PHOTODIODE
LENS
Figure 2. The Stack Optical Convolution Velocimeter.
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Figure 3. The Sensor Head of the Stack OCV.
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Figure 4. Close-Up of the Mirror-Grating of the Stack OCV.
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SECTION 5
TESTING AND EVALUATION OF THE STACK OCV
PURPOSE OF TESTS
Tests have been performed to evaluate the performance of the stack OCV.
These tests were of two types. First, the accuracy of the OCV was ascertained
in BBN's own wind tunnel as a function of tunnel speed and angle of incidence.
The second set of tests were performed at the EPA's Simulated Stationary
Source Facility (SSSF) at Research Triangle Park and were to evaluate the
performance of the stack OCV under adverse environmental conditions. These
tests would show if, or how, hot and dirty flows would affect the accuracy
of the OCV.
CALIBRATION OF TIME BASE
The OCV is inherently an absolute instrument in the sense that it does
not need calibration. The grating lines on the OCV are each 1 mm wide and,
therefore, a 10 kHz crossing frequency corresponds to a speed of 20 m/sec.
In the OCV display, the frequency is counted for an appropriate period to
give a number which corresponds to this speed. Thus, the time base of the
counter was adjusted so that an input frequency of 10 kHz (from a signal
generator) gave a reading of 20. This was the only adjustment made to the
unit. All subsequent readings were taken without any further adjustments.
CALIBRATION OF OCV IN BBN WIND TUNNEL
The stack OCV was set up in the BBN low speed wind tunnel and compared
with a pitot tube whose pressure was read on a slant tube manometer, Figure
5 compares the OCV readings with the pitot tube readings, which had to be
corrected for atmospheric temperature and pressure. Two heater wire diameters
were tested (.375 and .21 mm diameters) but no significant difference was
found. There was no difference in the mean readings of the OCV and pitot
tube and the standard deviations was 1.1%. The largest differences were at
low speeds where the pitot tube was difficult to read.
The second series of measurements was to determine the sensitivity of the
OCV to its angle of incidence. The OCV was rotated about its axis and the
readings recorded at a constant tunnel speed. We would expect the OCV to
vary as the cosine of the angle of incidence since it measures the velocity
perpendicular to the grating lines. Figure 6 shows the results obtaining at
four tunnel speeds. The root-mean-square difference between the measured
result and the cosine response was computed for each speed and the results
shown in Figure 6.
10
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o
O>
in
CALIBRATION
.37 mm HEATER
.21 mm HEATER
MEAN-0.0%
STANDARD
DEVIATION" 1.1%
PI TOT (m/sec)
Figure 5. Calibration in BBN Wind Tunnel
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0)
o
o
RMS ERROR
FROM COSINE = 1.9%
RMS ERROR
FROM COSINE = 1.0%
RMS ERROR
FROM COSINE = 2.0%
RMS ERROR
FROM COSINE =15%
-30
-20
-10 0 10
ANGLE OF INCIDENCE
20
Figure 6. Angle of Incidence Sensitivity.
12
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EVALUATION IN THE SSSF
After the stack OCV had been tested at BBN, it was shipped to the EPA
laboratory at Research Triangle Park in North Carolina for tests in the SSSF.
During these tests, the SSSF simulated combustion conditions with respect to
temperature, humidity and dust. The OCV was inserted into the test duct
through a port and located close to the center of the duct, where a pitot
tube was also mounted, for comparison purposes. The pitot tube output was
monitored with a "Magnehelic" instrument. The standard tunnel instrumen-
tation was used to measure tunnel temperature and dust loading. Separate
instrumentation was used to measure humidity. The equipment set up is shown
in Figure 7.
Tests were performed under a wide range of conditions and these are sum-
marized in Table 1. Twelve tests were conducted. The speed range covered
was generally 3-20 m/sec except at elevated temperatures where the speed
could not be allowed to drop below 11 m/sec or the electric heaters will
become too hot.
TABLE 1. TEST MATRIX FOR SSSF.
Run Temperature
No. °C
1
2
3
4
5
6
7
8
9
10
11
12
105
105
105
27
28
28
152
147
170
198
25
25
Humidity
% by Vol
Dust
Feed
Rate
kg/hr
0.5 0
8.0(?) 0
14. 9(1
0.5
0.5
0.5
0.5
4.7
0.5
0.5
0.5
0.5
) 0
0
5-10
23
0
0
0
0
.7,1.
1.4
Dust
Loading
mg/m
0
0
0
1400
100-1400
600-4000
0
0
0
0
4 20-200
40-200
Velocity Range
m/sec Comments
11
11 -
11 -
3.5 -
3.5 -
3 -
12 -
12.5 -
13.5 -
12 -
3.5 -
3.5 -
20
20
20
20
20
20
20
20
16.5
20
20
20
Warn
Humid
Very Humid
Ambient
Moderate Dust
Heavy Dust
Hot
Combustion Gases
Hot
Hot
Fine Dust
Electric Arc
Furnace Dust
Figures 8 through 17 show the results of the tests. Each figure compares
the OCV and pitot tube, computes the mean difference and the standard devia-
tion of the differences. The pitot tube had to be corrected for the facility
temperature and humidity (the dust loadings used should not have affected the
13
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Figure 7. Stack OCV Set Up in the Stationary Source Simulation Facility
(SSSF).
i i
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20
u
o>
in
RUN 2
15
3 10
>
o
o
10 15
PI TOT (m/sec)
Figure 8. Run 1 - Warm 105°F.
MEAN=+26%
STANDARD
DEVIATION* 2.0 %
20
25
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«J
20
15
^ 10
RUN 2
Figure 9.
10 15
PITOT (m/sec)
Run 2 - Humid, 8.0% H20 and 105°C.
ME AN =-1-5.5%
STANDARD
DEVIATION = 2.2%
20
25
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u
O>
20
15
.3 10
>
o
o
RUN 3
10
ME AN =+6.6%
STANDARD
DEVIATION'2.5%
15
20
25
PITOT (m/sec)
Figure 10. Run 3 - Very Humid, 14.9% H20 and 105°C
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oo
o
0>
(A
O
o
MEAN = -0.8%
STANDARD
DEVIATION* 2.1%
10 15
PITOT (m/sec)
Figure 11. Run 4 - Ambient, 27°C.
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-------
u
O>
O
O
MEAN = -6.8%
STANDARD
DEVIATION* 1.5%
• HEATER
O DUST ALONE
10 15
PI TOT (m/sec)
Figure 13. Run 6 - Heavy Dust Loading, 600- 4000 mg/MJ
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o
0»
O
O
MEAN' 1.6%
STANDARD
DEVIATION '2.0%
10 15
PITOT (m/sec)
Figure 14. Run 7 - Hot, 152°C,
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u
tt>
O
O
ME AN =1.7%
STANDARD
DEVI AT ION* 4.2%
PITOT(m/sec)
Figure 15. Run 8 - Combustion Products, 4.7% H20 and 147°C.
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N3
U>
o
O
O
MEAN»-15%
STANDARD
DEVIATION* 4.3%
10 15
PITOT(m/sec)
Figure 16. Run 10 - Very Hot, 170°C,
-------
ME AN = -1.3%
STANDARD
DEVIATION* 4.9%
• HEATER
O DUST ALONE
10 15
PI TOT (m/sec)
Figure 17. Run 11 - Fine Dust, 20 - 200 mg/MJ
-------
20
RUN 12
15
10
>
o
o
5 10 15
PI TOT (m/sec)
Figure 18. Run 12 - Electric Furnace Dust, 40 - 200
MEAN =+3.4%
STANDARD
DEVIATION »6.5%
• HEATER
ODUST ALONE
20
3
25
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pitot readings). The mean differences for the humid runs 2 and 3 of 5.5% and
6.6%, respectively, are larger than can be accounted for by statistical errors.
However, the differences can be accounted for by humidities of 23% and 32.5%
by volume instead of the 8% and 14.9% measured. This discrepancy could have
arisen from condensation in the line to the humidity measuring instrument,
causing an erroneously low reading for the humidity.
Run 6, heavy dust loading, had a mean difference of 6.8%. This probably
arose from the large low frequency component of the signal from the OCV due to
obscuration by dust. This is thought to cause distortion in the signal analy-
zer. However, this only occurred at very heavy dust loadings.
This same effect was noticed, to a lesser extent, at moderate dust load-
ings and elevated temperatures, particularly at higher tunnel speeds. The low
frequency components in the signal tends to pull the signal processor down
below the true frequency. These low frequency components arise from clouds of
dust or refraction effects in the hot flow. These components could be removed
by a high pass filter.
We also examined whether the dust was, by itself, sufficient seeding for
the flow and whether or not a heater was required. To do this we rotated the
OCV 180° so that the heater was downstream. The reading was then taken in
that position as well as with the heater upstream. However, as Figures 12,
13, 17, and 18 show, the accuracy with dust alone was not as good as with the
heater. The reason for this was probably the weaker signal with dust alone
and the large low frequency component present. No significant difference in
the accuracy was noted with the different size dust particles.
VISUAL INSPECTION
After all the tests had been completed in the SSSF, the stack OCV was
dismantled to see if there was any significant deterioration. In fact, the
inside of the OCV proved to be in very good condition. The teflon plastic
lamp and fiber optic hold was in good condition and the electrical wiring
showed no deterioration. However, the end of the fiber optic cable did show
some blackening, indicating that the epoxy used to cement the ends of the
fibers together had decomposed. This, however, did not interfere with the
performance of the instrument.
26
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-78-049
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
DEVELOPMENT OF AN OPTICAL CONVOLUTION VELOCIMETER FOR
MEASURING STACK FLOW
5. REPORT DATE
March 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
M. J. Rudd
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Bolt Beranek and Newman, Inc.
Cambridge, MA 02138
10. PROGRAM ELEMENT NO.
1AD712 RA-?Q fFY-77'
11. CONTRACT/GRANT NO.
EPA-IAG-D6-F044
12.
in Ancwr*v MAMC AMI-* A rtnoccc
Environmental Sciences Research Laboratory-RTP, NC
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park. North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final 7/76 - 1/77
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES BBN executed the development under an interagency agreement that
EPA had with the Air Force Flight Dynamics Laboratory, Dept. of the Air Force.
Wright-Patterson Air Force Base, OH 45433
16. ABSTRACT
A new type of instrument has been developed and tested for the measurement of
stack flow velocities. The instrument is optical and generates a shadowgraph pattern
of the wake from a small heater. This shadowgraph is projected on a mirror grating of
precise dimensions and the reflected light detected by a photodiode. The output of
the photodiode fluctuates at a frequency that is related to the velocity with which
the turbulence is converted across the grating. By measuring this frequency, the
flow velocity is determined.
A version of this optical convolution velocimeter (OCV), as it is called has
been built to withstand a temperature of 200°C and combustion gases. This unit has
been tested in both a wind tunnel and EPA's stationary source simulation facility
(SSSF). The agreement with a pitot tube was close, 1% in the wind tunnel and
2 - 2.5% in the SSSF. Some difficulty in signal processing was found at high
speeds and high temperatures or dust loadings, but this can be cured.
The OCV promises to be a much more accurate and easier to use instrument than
the pitot tube, at little additional cost.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
* Air pollution
* Development
* Optical equipment
* Speed indicators
Flue gases
Tests
13B
20F
14B
21B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport!
UNCLASSIFIED
21. NO. OF PAGES
35
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION Is OBSOLETE
27
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