SULFATE SAMPLING DILUTION TUNNEL
DESIGN AND VALIDATION
by
Melvin N. Ingalls
FINAL REPORT
of
Task No. 6
Contract 68-03-2196
Prepared for
Environmental Protection Agency
Office of Mobile Source. Air Pollution Control
Emission Control Technology Division
Ann Arbor, Michigan 48105
June 1977
SOUTHWEST RESEARCH INSTITUTE
SAN ANTONIO CORPUS CHRISTI HOUSTON
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SOUTHWEST RESEARCH INSTITUTE
Post Office Drawer 28510, 6220 Culebra Road
San Antonio, Texas 78284
SULFATE SAMPLING DILUTION TUNNEL
DESIGN AND VALIDATION
by
Melvin N. Ingalls
FINAL REPORT
of
Task INo. 6
Contract 68-03-2196
EPA Project Officer: Richard D. Lawrence
Prepared for
Environmental Protection Agency
Office of Air and Waste Management
Office of Mobile Source Air Pollution Control
Emission Control Technology Division
Ann Arbor, Michigan 48105
June 1977
Approved:
Karl J. Springer, Director
Department of Emissions Research
Automotive Research Division
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FOREWORD
This project was conducted for the U. S. Environmental Protection Agency
by the Department of Emissions Research of Southwest Research Institute (SwRI).
Work was begun on April 26, 1976, and completed on June 25, 1977. The project
was conducted under Task 6 of Task Order Contract 68-03-2196. It was identified
within Southwest Research Institute as Project 11-4291-008.
The EPA Task Officer for this task was Richard D. Lawrence of the Emission
Control Technology Division, EPA, Ann Arbor, Michigan. Karl J. Springer,
Director, Department of Emissions Research at SwRI served as Project Manager.
The task was under the supervision of Melvin N. Ingalls, Senior Research
Engineer. The initial tunnel design was done by Terry Ullman, Research Engineer,
and the final drawings were made by Bob Nye. Although a nurober of Department of
Emissions Research personnel were involved in the project, key personnel in-
cluded Nathan Reeh, technician, who constructed the tunnel; Tom Jack, senior
technician and Dolores Bynum, laboratory assistant, who assisted in the test
phase; and James Herrington, lead technician, and Shelly Stevens, laboratory
assistant, who performed the various chemical analyses required.
Several project reviews were held both at SwRI and at the EPA laboratory
in Ann Arbor, Michigan. The reviews at SwRI were on April 15, 1976, and Novem-
ber 22, 1976. The reviews at Ann Arbor were on October 1, 1976, and December
10, 1976. In addition to these reviews, frequent telephone conversations pro-
vided close liaison between EPA and SwRI during the project.
11
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ABSTRACT
This report describes the design features and development testing of
a dilution tunnel for sampling automotive sulfate emissions. The design of
the dilution tunnel and sampling system was the result of a concensus of
ideas from representatives of the EPA and industry. The development testing
included a propane traverse to verify exhaust mixing; testing the critical
flow sampling system; development and use of a sulfate mist generator to
determine system sulfate recovery; and evaluation of system losses using
automotive exhaust.
The propane traverse demonstrated acceptable exhaust gas mixing. The
original design sample flow rate could not be maintained because the pressure
drop across the sulfate filter caused the critical flow sample system to un-
choke.
While system losses were acceptable using the acid mist generator, the
system was found to have unacceptable sulfate losses at tunnel temperatures
above 85°C (185°F) when tested with automotive exhaust. These losses appeared
to be a function tunnel temperature, with losses increasing as tunnel tempera-
ture increased. The losses were minimized by increasing the dilution air flow
which lowered the tunnel temperature. Sulfate losses in the connecting tubing
between the car exhaust pipe and sulfate tunnel were found to increase con-
siderably as the tubing length increased. At the completion of the develop-
ment tests, the sampling system, including the tunnel and sampling and control
console, was delivered to EPA, Ann Arbor. A complete set of drawings of the
tunnel was furnished with the tunnel.
111
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TABLE OF CONTENTS
Page
FOREWORD ii
ABSTRACT iii
LIST OF TABLES vi
LIST OF FIGURES vii
SUMMARY viii
CONCLUSIONS x
I. INTRODUCTION 1
A. Objective 1
B. Approach 1
II. DESIGN FEATURES 3
A. Preliminary Design Considerations 3
B. Tunnel Design 3
C. Sample Probe Design 4
D. Sampling and Control System 7
E. Design Modifications Resulting from Test Program 11
III. SULFATE MIST GENERATOR EXPERIMENTS 12
A. Development of Mist Generator 12
B. Aerosol Sizing Tests 14
C. Sulfate Recovery Tests 21
D. Tunnel Propane Traverse 22
IV. TEST WITH AUTOMOTIVE EXHAUST 25
A. Equipment and Procedures 25
B. Initial Probe Loss Tests 25
C. System Sulfate Losses as a Function of Temperature 28
D. Effect of Connecting Tubing Length 32
V. SYSTEM MODIFICATIONS 34
A. Critical Flow Sample Rate Evaluation 34
B. Methods to Reduce Tunnel Temperature 34
1. Cooling Dilution Air 38
2. Increase Amount of Dilution Air 38
C. Final System Modifications Chosen 39
LIST OF REFERENCES 41
IV
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APPENDICES
A. Statement of Work
B. Velocity Traverse of 21 cm Diameter Tunnel
C. Mist Generator Calibration Data
v
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LIST OF TABLES
Table Page
1 Sulfate Recovery From Mist Injection Tests 21
2 Sulfate Probe Loss Tests 25
3 Results of Probe Loss Tests 26
4 Tunnel Temperature Effects Test Schedule 29
5 Summary of System Sulfate Losses 29
6 Effects on Connecting Tubing Length 33
7 Maximum Exhaust Temperature During Dynamometer Operation 38
for Three Cars
8 Test Schedule with Large CVS 40
9 Results from Tests with Large CVS 40
VI
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LIST OF FIGURES
Figures Page
1 Schematic of Sulfate Sample Dilution Tunnel 5
2 Photographs of Sulfate Dilution Tunnel 6
3 Sulfate Sampling Probe Tips , 8
4 Modified 47 mm Filter Holder 9
5 Sampling and Control Console 10
6 Baird-Atomic Mist Generator 13
7 Sulfate Mist Injection Equipment 15
8 Andersen Impactor 16
9 Sizing Tests Equipment Schematic 18
10 Modified Mist Generator 19
11 Results of H2SO4 Mist Sizing Tests 20
12 Tunnel Traverse During Propane Injection 23
13 Percent Probe Loss Versus Sulfate Through Probe 27
14 Percent 804= on Tunnel Versus Tunnel Temperature 31
15 Percent SO^~ on Probe Versus Tunnel Temperature 31
16 Percent 804" Lost on Sulfate Sampling System Versus
Tunnel Temperature 32
17 Calibration of SwRI Built Critical Flow Nozzle 35
18 Pressure Drop Across Clean 47 mm Fluoropore Filter 35
19 Capacity Curve for Cast 2565 Pump 37
vii
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SUMMARY
A dilution tunnel and sulfate sampling system to be used with both the
positive displacement pump (PDF) and critical flow venturi (CFV) constant
volume sampler (CVS) emission sampling systems was built from EPA design cri-
teria. The system uses a 2.7 m (8.8 ft) long by 21 cm (8.4 in.) inside dia-
meter stainless steel pipe as the dilution tunnel. Exhaust mixing length in
the tunnel is approximately 1.74 metres (68.5 in.).
The sulfate probe is of 2.54 cm (1 in.) stainless steel tubing approxi-
mately 61 cm (24 in.) long with a removable tip which reduces the probe dia-
meter to that necessary to provide isokinetic sampling. For the CFV-CVS system,
this removable tip contains a convergent-divergent section designed to operate
in the choked flow regime. The probe inlet is centered in the tunnel, with the
holder for the sulfate filter located outside the tunnel,
An alarm system is furnished to provide an audible and visible alarm when-
ever the tunnel temperature is outside a specified range. Another alarm is
activated whenever the pressure downstream of the probe critical flow nozzle
increases to the point that the nozzle flow becomes- unchoked. Controls are also
provided for the air heaters installed in the dilution air plenum.
The development testing performed included a propane traverse to deter-
mine the extent of exhaust mixing; proof testing of the CFV-CVS sampling
system; development and use of a sulfate mist generator to determine system
sulfate recovery; and evaluation of system losses using actual automotive
exhaust. The propane traverse showed that the maximum and minimum propane con-
centrations were within approximately ±5 percent of the average. This spread
was considered small enough not to affect the accuracy of the sulfate sample.
A SET-7*test was run with the critical flow nozzle sample probe used with
CFV-CVS units. The test revealed that the originally planned sample rate of
0.028 m^/min (1 cfm) resulted in the nozzle unchoking as the pressure drop
across the filter increased due to sulfate loading. As a result, the sample
flow was changed to 0.014 m3/min (0.5 cfm) for both the POP and CFV-CVS systems.
A sulfuric acid mist generator was developed which injected sulfuric acid
into the tunnel at a rate approximating automotive exhaust. Approximately 80
percent of the mist generated was less than one micron in size. The sample
filter recovered an average of 105 percent of the acid injected. Accuracy
limits of the analytical procedures are probably responsible for recoveries
greater than 100 percent. Improved analytical methods were developed for
future work. Probe losses were approximately 3 percent at a tunnel temperature
of 55°C (131°F). While a great deal of progress was made on both the mist
generation and sulfate recovery procedures, more work is needed to perfect both.
Tests with car exhaust revealed that probe and tunnel losses were a func-
tion of tunnel temperature, increasing as temperature increased. The total
system losses (excluding the connecting piping) varied from 3.9 percent at
68°C (155°F) to 21.6 percent at 96°C (205°F). The type of probe material ap-
peared to make some difference in the amount of sulfate lost on the probe.
However, at 85°C (185°F) average temperature probe losses were above 25 per-
cent with stainless steel, Teflon and glass probes. There was also some indi-
* SET-7 is the congested freeway driving schedule.
viii
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cation that the system would become "seasoned" and that sulfate losses would
decrease with test time. A test of the critical flow sample probe nozzle
showed higher sulfate losses than the noncritical flow nozzle (15% vs. <3%)
at about 70°C tunnel temperature.
For this project,a 1588 kg (3500 Ib) inertia weight car with a 4.98
litre (304 CID) engine was used. The tunnel temperature during SET-7 tests
run with this car were higher than permissable for acceptable sulfate losses.
A brief check of exhaust temperatures of several cars revealed that for
many cars, a 9.20 mVmin. (325 cfm) CVS may not produce low enough tunnel
temperatures for acceptable sulfate losses. To minimize system sulfate losses
the tunnel temperature should be as low as possible, yet still above the dew-
point of the dilute exhaust. To do this, either the dilution air tempera-
ture must be lowered or its volume increased. The choice for this study was
to increase the volume.
A 14.73 m3/min (520 cfm) CVS was used for a series of tests with the
same test car used in the previous tests. For a SET-7 test, the average
temperature was reduced to 59°C (138°F) from about 85°C (185°F) for a SET-7
test with a 9.20 m3/min (325 cfm) CVS.
During these tests the sample probe with the critical flow nozzle was
used. Probe losses with the critical flow probe averaged 19 percent compared
with the less than 3 percent for the noncritical flow probe at a CVS flow of
9.2 m3/min (325 cfm) and approximately the same average tunnel temperature.
While time did not permit further investigation of the sulfate losses with the
critical flow probe, it is recommended that a thorough investigation of the losses
with this probe be conducted prior to using this system for routine sulfate test-
ing.
Two different lengths of connecting tubing between the car exhaust and
the tunnel were tested for sulfate losses. The car was run for 25 minutes at
64 km (40 mph) to generate the exhaust sulfates. The loss in the 0.61 metre
(2 foot) pipe was approximately 0.6 percent; the loss in the 4.57 metre (15
foot) pipe was approximately 20 percent.
The sampling system, including pump, flow meters and controls was fit-
ted into a console together with the alarm system and heater controls. This
console and the dilution tunnel itself were shipped to EPA, Ann Arbor at the
completion of the test phase of this project. A complete set of drawings of
the tunnel was also furnished with the system.
IX
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CONCLUSIONS
The following conclusions can be drawn from the testing performed with
the 21 cm diameter dilution tunnel.
1. Tunnel and sample probe sulfate losses are a function of tunnel
temperature, with losses increasing as temperature increases.
2. The sulfuric acid mist generator developed during this project can
be used to determine system sulfate recovery, however the proce-
dure needs further refinement.
3. The tunnel design provides adequate mixing of car exhaust gas
and dilution air.
4. There is considerable sulfate lost when connecting tubing on the
order of five metres long is used between the car exhaust and the
dilution tunnel.
5. The sample flow rate for the critical flow sample probe nozzle
designed for use with a CFV-CVS should be at or below 0.014 m3/min
(0.5 cfm) because of high filter pressure losses.
6. Sulfate losses using the critical flow sample probe nozzle are
higher than losses on the noncritical flow nozzle at the same
tunnel temperature.
7. For many cars, a 9.20 m^/min (325 cfm) capacity CVS may not pro-
duce low enough tunnel temperatures for acceptable sulfate losses
without precooling the dilution air.
x
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I. INTRODUCTION
Past EPA studies showed that cars equipped with catalytic converters emit-
ted more sulfates than noncatalyst cars.^"^' With the possibility of the
routine testing of prototype cars for sulfate emissions, the need for a stan-
dardized sulfate sampling system became evident.
In an effort to develop an acceptable standard sulfate sampling system
for use by the EPA Mobile Source Pollution Laboratory at Ann Arbor, Michigan,
and hopefully by the auto industry as well, a meeting was held on December 4,
1975 at the EPA, Ann Arbor, facility with representatives of the EPA, the auto
manufacturers, and Southwest Research Institute in attendence. From this meet-
ing a general design consensus and criteria for a sulfate sampling system
emerged.
A. Objective
The objective of this project was to build and test a suitable sulfate
dilution tunnel and filter collection system based on SwRI's mini-tunnel de-
sign which was used extensively in previous sulfate testing projects for EPA
(2,4)_ The new tunnel was to use design criteria established at the Decem-
ber 4, 1975 meeting at Ann Arbor between EPA and industry. Once built, the
tunnel was to be used to investigate ways to achieve a calibration with sul-
furic acid mist; determine the effect of exhaust connecting tubing length;
determine the effect of dilution air humidity; and compare this 21 cm (8 inch)
diameter tunnel to a 46 cm (18 inch) diameter tunnel.
B. Approach
To meet the objectives of the project, a 12 item Statement of Work was
agreed upon by EPA and SwRI. The complete Statement of Work is included as
Appendix A. The Statement of Work was later modified to include furnishing
the necessary hardware for a complete sampling system and to add additional
testing to better define the system sulfate losses discovered during the
test program.
Briefly the plan was to: (1) build the tunnel to the agreed upon speci-
fications; (2) develop a sulfuric acid mist injection system; (3) determine
the sulfate sampling system recovery using the sulfuric acid mist injection
system; (4) compare the sulfate levels obtained from steady-state and sul-
fate cycle tests on an actual car with sulfate levels obtained using an 18
inch dimater tunnel on the same car and test cycles and; (5) evaluate the
effects of connecting tubing length between car and tunnel using a 2 foot
long piece of flexible tubing. At the completion of the test program, a
complete set of drawings would be made incorporating any changes found nec-
essary during the test program.
During the project the test plan was modified to delete the comparison
of the small tunnel and the 18 inch diameter tunnel and to delete the tests
*Superscript numbers in parentheses refer to the List of References
at the end of this report.
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to determine the effect of humidity. In place of these tests, a series of
tests were performed to define the system losses as a function of tunnel
temperature.
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II. DESIGN FEATURES
The design considerations and physical layout of the sulfate tunnel,
probe and sampling and control system are explained in this section of
the report.
A. Preliminary Design Considerations
As mentioned in the Introduction, a planning meeting was held in Ann
Arbor between EPA and industry for the purpose of agreeing on a set of
design parameters for a sulfate dilution tunnel sampling system. The fol-
lowing parameters were agreed upon:
The dilution tunnel diameter will be approximately 8 inches
The distance between the exhaust inlet and the probe tip will
be 8 pipe diameters
The distance between the probe tip and the downstream end
of the tunnel will be 2.5 pipe diameters
The tunnel material will be stainless steel
A mixing orifice will be located at the plane of the
exhaust inlet
The probe will be made of stainless steel tubing
The filter holder will be outside the tunnel
The EPA added the following requirements to meet their particular
needs:
Provide mixing of the exhaust and dilution air
Be compatible with a CVS flow rate of 325 SCFM at
typical dilution tunnel operating conditions of
735 mm HgA and 66°C
Be compatible with EPA certification test cells
Sample system to be able to be used with a critical
flow venturi (CFV)-CVS and a positive displacement
pump (PDF) - CVS
B. Tunnel Design
From the criteria listed above the basic tunnel system was chosen.
The tunnel was constructed of 8 inch schedule 5 welded stainless steel pipe.
This pipe had an inside diameter of 21.4 cm (8.41 inches) and a wall thick-
ness of 2.77 mm (0.109 inches). This fixed the distance between the exhaust
inlet plane and the probe tip at 170.7 cm (67.2 inches), and the distance
between the probe tip and the tunnel exit at 53.3 cm (21.0 inches). The
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overall length of the tunnel is 2.67 metres (8.75 feet). Provision was made
for the exhaust to enter from either side of the tunnel using a 7.6 cm (3
inch) diameter elbow through a 15.2 cm (6 inch) Tri-Clover (Ladish Co.)
coupling. The exhaust discharges into the tunnel in the downstream direction.
A 15.2 cm (6 inch) mixing orifice is located in the tunnel at the plane of
the exhaust discharge. The diluted exhaust exits the tunnel through a nominal
4 inch stainless steel pipe approximately 11 cm (4.5 inches) long. A 15.2 cm
(6 inch) Tri-Clover coupling installed in the top rear of the tunnel is used
for the sample probe port. To better fit the EPA certification test cells and
utilize minimum floor space, the dilution air filter box was placed above the
tunnel. In addition to the usual filters, the dilution air inlet plenum was
equipped with duct heaters to allow the sulfate tunnel to be pre-heated. It
also allows the tunnel to maintain a minimum temperature above the condensation
temperature of the mixed stream during a test. Figure 1 is a schematic of the
tunnel showing some of the more pertinent dimensions. Figure 2 contains photo-
graphs of the tunnel from various angles.
C. Sample Probe Design
The sample probe was made from 2.54 cm (1 inch) stainless steel tubing
with 1.24 mm (0.049 inch) wall thickness and is approximately 61 cm (24 inches)
long. The probe is fitted with an interchangeable nozzle tip(s) to provide iso-
kinetic sampling. When installed, the probe tip points directly upstream. There
is a single 45 degree bend in the probe. The probe comes out of the tunnel at a
45 degree angle through a 15.2 cm (6 inch) Tri-Clover coupling. The filter
holder is located outside the tunnel at the end of the probe. The initial sample
flow rate specified by EPA was 0.028 m3/min (1 cfm).
Part of the design criteria for the tunnel was that the sulfate sampling
system be able to be used with a CFV-CVS. The CFV-CVS is in reality a propor-
tional sampler. Since the flow is controlled by a critical flow venturi, the
volumetric flow is a function of the gas stream pressure and temperature. The
gaseous emissions sample lines of a CFV-CVS also have choked flow sections so that
the sample taken is proportional at all times to the total volume flowing through
the CFV-CVS. Therefore, the sulfate sampling system must also be proportional
at all times to the total volume flowing through the CVS. To do this, the sulfate
sampling system must also have a critical flow section. After much discussion of
the best way to accomplish this, it was decided to use a choked convergent-
divergent nozzle at the sample probe inlet. This arrangement will give sulfate
sample flow proportional to the total CFV-CVS volume flow, providing the tem-
perature difference between the sulfate probe entrance and the CVS venturi is
negligible.
Using a total pressure traverse previously performed on a similar tunnel,
the velocity at the center of the tunnel was found to be 125 percent of the
bulk velocity. See Appendix B. Thus, for a 325 cfm CVS at 735 mm of mercury
and 66°C,the velocity seen by the probe is 5.89 m/sec (19.3 ft/sec). This
fixed the nozzle inlet diameter for 0.028 m3/min (1 cfm) at 10.1 mm. Using
standard compressible flow calculations(5), the nozzle throat was calculated
to be 1.59 mm.
For smooth transition, the angles for the converging and diverging section
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to sample
pump
dilute exhaust
to CVS
filter holder
dilution
air
filter
pack
Heaters
2.49 metres
Figure 1. Schematic of Sulfate Sample Dilution Tunnel
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Figure 2. Photographs of Sulfate Dilution Tunnel
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of the nozzle were set at 15 degrees for each. The nozzle length was set
so that the entrance was tapered for approximately 2 nozzle diameters.
For a positive displacement pump (PDF) CVS the critical flow section
is not used. Since the testing to be performed at SwRI would be with a PDP-
CVS, a second nozzle was designed without the converging-diverging section.
Sketches of both nozzles are shown in Figure 3.
At the request of the EPA, the standard 47 millimeter Fluoropore (Milli-
pore Corporation) filterholder was modified with quick connects on each end.
The inlet end was replaced with a new, longer, diverging section, and a Viton "0"
ring to seal the filter. The male part of a 1 inch quick connect was machined
into the end of the filter holder entrance piece. The discharge side was
drilled and tapped with 1/2 inch pipe threads and the stem of a 1/2 inch full
flow quick connect installed. A sketch of the filter holder is shown in Fig-
ure 4.
D. Sampling and Control System
The original intent of this project was that SwRI would provide to EPA,
Ann Arbor, only the sulfate tunnel and probe, with the EPA to furnish the
remainder of the sampling system. During the course of work, the EPA modified
the scope of the project to include a complete sampling and control system.
A picture of the sampling and control console is shown in Figure 5. The con-
sole contains: (1) sample system including pump, flow meters and controls;
(2) alarm system to indicate loss of critical flow and failure to remain with-
in temperature limits; and (3) dilution air heater controls.
The sample system consists of a sample drier tube filled with a molecular
sieve, a Cast Model 2565 vacuum pump, a rotameter for visual indication of
instantaneous flow rate and an American Meter Division Gas Sampling meter for
total sample volume measurement. An interconnect is provided to allow the
sample pump to be turned on and off from the CVS control panel.
The alarm system was designed at the request of the EPA to provide an
audible and visible alarm whenever the tunnel temperature is outside a speci-
fied temperature range (high or low). Another alarm is activated whenever
the pressure behind the sulfate sample probe critical flow nozzle increases
to the point that the nozzle becomes unchoked.
The controls for the heaters in the dilution air plenum allow the amount
of heating to be controlled manually or automatically. Three different levels
of heating are provided under manual operation. A temperature controller pro-
vides for automatic heater control for a given tunnel temperature. It should
be recognized that the temperature controller provides control on the minimum
tunnel temperature only. During a test, if the dilute exhaust temperature
exceeds the tunnel set point temperature, the heaters would shutoff and the
tunnel temperature would be dependent on the car exhaust and ambient air tem-
peratures until the tunnel temperature again fell below the set point. An
interconnect is also provided to permit the heaters to be operated only when
the CVS blower is on. This keeps the heater elements from burning-out from
overheating.
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2.54 cm
Sulfate Probe Tip for CFV-CVS Systems
Sulfate Probe Tip for PDP-CVS Systems
Figure 3. Sulfate Sampling Probe Tips
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To Sample Pump
Modified Discharge side
of Millipore 47 mm filter holder f
Swagelok 1/2" Full Flow
Quick Connect Coupling
Redesigned inlet portion of
filter holder with intergral
quick connect coupling stem
f
al
m
C,.
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r
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r
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^^^^^ t>wageloK ±" lull flow auick
^jjjiiijjiii~~ connect coupling body
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From Sample Probe
Figure 4. Modified 47 mm Filter Holder
9
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gas meter
temperature
heater
switches
pressure
alarms
i-o ff
switch
valve
n^n
n
n
•D
Q^~
Q-"
sample flow gas
meter readout
sample flow
rotameter
sample flow
control valve
heater temperature
controller
temperature
alarms
sample flow drier
sample pump
ampling and Control Console
10
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E. Design Modifications Resulting From Test Program
As the result of the tests described in Sections III, IV and V, some
modifications to the sampling system were required. The CVS volume flow
was increased to 15 m3/min (530 cfm) with 19.8 m3/min (700 cfm) as an al-
ternative for the CFV-CVS and the sulfate sample flow decreased to 0.014 m3/min
(0.5 ft3/min). This required the resizing of the sulfate sample probe tips.
While the internal dimensions changed somewhat, the configuration of each tip
remained the same as that shown in Figure 3.
11
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III. SULFATE MIST GENERATOR EXPERIMENTS
One of the goals of this project was to do preliminary development
and evauation of a sulfate injection method of calibrating the complete
tunnel sampling system similar to the propane test used for the CVS gaseous
emission sampling system. This section of the report covers the development
of the mist generator and its use in determining system recovery.
A. Development of Mist Generator
The first step in developing a sulfate calibration system was finding
a mist generator that would produce the required mist size (98 percent less
than 1 micron) in an amount equivalent to an automobile exhaust (about 7 mg/
min of H2SO4). The design of the system should also be such that it is rela-
tively easy to determine the amount of sulfuric acid injected into the tunnel.
Several mist generators were investigated including Collison type generators
from several manufacturers, Sierra Instruments Spinning Disc Aerosol Generator,
the "Misto-Gen"ultrasonic generator, and others. For most of these generators,
it appeared to be difficult to determine accurately how much sulfuric acid
mist would be generated for a given test.
After discussing the problem with Dr. Paul Lamoth of the EPA (Research
Triangle Park, North Carolina), who was working in the field of atmospheric
monitoring of aerosols and had used several of the mist generators under con-
sideration, it was decided to use the calibration mist generator from a Baird
Atomic atmospheric sulfuric acid analyzer.
This mist generator was all glass with short flow passages, so that it
would be easy to recover the residual sulfuric acid from the generator. A
drawing of this generator is shown in Figure 6.
The generator produces a mist by breaking up droplets of dilute sulfuric
acid with compressed air. The acid is admitted into the generator through a
capillary tube attached to a small funnel. As the acid drips into the mist
chamber, it hits the air jet from the compressed air nozzle and is broken up
into a mist. A piece of glass tubing connects the generator to the tunnel.
Not all of the acid entering the chamber left as an aerosol mist. The
larger particles from the droplet impinged on the side of the chamber and
ran down to the bottom of the chamber. There was also considerable conden-
sation on the walls of the mist generator.
The original generator was modified by placing a stopcock in the cham-
ber drain line. If the chamber became too full, some of the residual acid
was drained from it. However, some liquid was always left in the chamber
so that no mist would escape through the drain.
The proposed test procedure began with feeding a given amount of dilute
sulfuric acid of known normality into the mist generator. Knowing the amount
and normality of the dilute solution, the amount of sulfate put into the gene-
rator could be calculated. After the test, the residual acid would be drained
from the generator and the generator and discharge tube rinsed with a small
amount of distilled water. The rinsing would be added to the residual acid
and the total volume measured. The normality of the mixture would be deter-
mined by titrating an aliquot of the mixture with sodium hydroxide. From the
12
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Dilute sulfuric acid in
Atomizer
B.A.-02561
Generator chamber
B.A. 02573
I I
I I
Residual dilute
sulfuric acid out
Compressed air in
Stopper
Mist outlet tube
Sulfuric acid mist out
Drain valve
Figure 6. Baird-Atomic Mist Generator
13
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volume and normality of the mixture, the amount of sulfate remaining in the
generator could be determined. Subtracting this amount from the total sul-
fate put into the generator would give the amount of sulfate injected into
the tunnel.
Preliminary bench tests were run with the generator using water to de-
termine the amount of liquid converted to mist, and to determine the air pres-
sure that gave the highest mist generation rate. The data from these tests
is contained in Appendix C. It was found that approximately 12 percent of
the dilute acid feed into the generator was atomized into mist. The optimum
air pressure was found to be about 138 kilopascals (20 psi). From these tests,
it was decided to use 100 ml of 0.2 N sulfuric acid as the mist generator feed-
stock. Figure 7 shows the mist generator set up to inject mist into the tunnel.
B. Aerosol Sizing Tests
An Andersen impactor was chosen as the easiest to use and most readily
available device for determining the size distribution of the sulfate aerosol
in the tunnel. Figure 8 shows the details of the impactor. The Andersen
Stack Sampling Head consists of a stainless steel case and 1/2" female pipe
fittings at the inlet and discharge. It is designed to be inserted directly
into the stack.
The Sampler contains nine jet plates each having a pattern of precision-
drilled orifices. The nine plates, separated by Teflon "O" rings, divide the
sample into eight fractions or particle size ranges. The jets on each plate
are arranged in concentric circles which are offset on each succeeding plate.
The size of the orifices is the same on a given plate, but is smaller for each
succeeding downstream plate. Therefore, as the sample is drawn through the
sampler at a constant flow rate, the jets of air flowing through any parti-
cular plate direct the particulates toward the collection area on the down-
stream plate directly below the circles of jets on the plate above. Since
the jet diameters decrease from plate to plate, the velocities increase such
that whenever the velocity imparted to a particle is sufficiently great, its
inertia will overcome the aerodynamic drag of the turning airstream and the
particle will be impacted on the collection surface. Otherwise, the particle
remains in the airstream and proceeds to the next plate. Since the particle
deposit areas are directly below the jets, seven of the plates act as both a
jet stage and a collection plate. Thus, No. 0 plate is only a jet stage and
No. 8 plate is only a collection plate.
For this project, a backup 0.5 micron Fluoropore filter was placed
on a plate 8 to trap all the remaining particulate. It should be pointed
out that the impactor is calibrated in terms of unit density (1 g/cc). It
can be readily seen that two objects of the same size, but different den-
sities, will have different inertial characteristics and would behave dif-
ferently in different environments. By referencing the sizes to unit den-
sity, the particles are measured in what is termed aerodynamic size. Par-
ticles of the same aerodynamic size behave aerodynamically as though they
were the same size, even though they have different physical sizes and
densities.
The size distribution was determined by washing each of the nine im-
pactor plates with 20 ml of 60 percent isopropyl alcohol solution and proces-
sing the solution using the Barium Chloranilate (BCA) procedure employed with
sulfate filters. The backup filter was processed using the usual BCA pro-
cedure for sulfate filters.
14
-------
Ring stand
100 ml burette
Sulfuric acid mist
generator
13 mm dia. glass tube
Sulfate
tunnel
Vehicle exhaust inlet
marmon flange
200 ml beaker
Figure 7. Sulfate Mist Injection Equipment
15
-------
SAMPLE FLOW
OUT
HOUSING
PLATE 8-
PLATE 0-
PLATE HOLDER
CONE
SAMPLE PLOW
IN
ISOKINETIC NOZZLE
Figure 8. Andersen Impactor
16
-------
The test set-up for the sizing tests using the Andersen impactor is
shown in Figure 9. The impactor is suspended in the tunnel at the same lo-
cation that is normally occupied by the sulfate probe. Preliminary tests
showed that while the Baird Atomic mist generator produced a sufficiently
fine mist, it did not produce a sufficient quantity for the desired accu-
racy of size determination from the impactor plates. Since the size distri-
bution was determined from the amount of sulfate on the plates, the more sul-
fate that could be put through the system, the more accurately the percent
of each size could be determined. Also, it was desired to have the amount
of sulfate be close to that generated by car exhaust. The target level was
about 130 mg per test.
In an effort to increase the quantity of mist, the generator chamber
was lightly heated by wrapping it with electrical heating tape. While this
increased the amount of aerosol to between 30 and 40 mg per test, this was
not deemed sufficient to represent automotive exhaust. The mist generator
was then modified by increasing the size of the chamber as shown in Figure
10. The objective of this modification was to allow more room in the gen-
erator chamber, reducing losses due to impingement of the droplets on the
walls. The modified generator did produce a greater amount of aerosol.
Although the amount of aerosol was still not quite to the level desired,
it was deemed adequate for development tests and the configuration was used
for the remainder of the project.
A total of nine sizing experiments were run, six of which were usable—
two tests with the original generator and four with the modified generator.
Each test consisted of placing the impactor in the tunnel and drawing a 22.7 £/
min (0.8 cfm) sample through the impactor while sulfuric acid mist was being
injected into the tunnel. The mist generator was fed with 100 ml of 0.2 N
sulfuric acid. This normally required about 25 to 30 minutes. The total
sulfuric acid injected into the tunnel varied from approximately 35 mg for
the original generator to approximately 60 to 110 mg for the modified generator.
The results of the sizing tests are shown in Figure 11. The amount of
sulfate mist below 0.4 microns (except for one test) varied from approximately
50 to 72 percent. The highest value was obtained with the sulfate mist gene-
rator in its original configuration. The lowest percentage was obtained with
the revised mist generator configuration. One test (10/22/76) showed only
25 percent of the mist below 0.4 micron. The reasons for this are not imme-
diately apparent. It may have to do with the amount of heating of the gene-
rator, or it may be the result of high residual sulfates on some of the sampler
plates. It was extremely hard to remove all residual sulfate from the plates.
Sometimes the residual sulfate indication would increase between two successive
cleanings.
Several things were learned from this series of tests. The first is
that the Andersen Impactor, though easy to use, has several deficiencies for
this type of aerosol sizing. It cannot separate particles smaller than 0.36
micron at the flow rate used. At the outset of this project, available in-
formation indicated that an aerosol mist below 1 micron would be sufficient
for simulating automotive exhaust. However, during the project, results from
the General Motors sulfate dispersion experiment^ ' became available which
indicated that exhaust sulfate particle size in the atmosphere was less
17
-------
00
Diluted
exhaust
to CVS
Rotameter
Pump
Dry
Gas
Meter
I molecular
seive
ndersen
Sampler
inside
tunnel
Vehicle exhaust
inlet flange
Dilution air plenum
Figure 9. Sizing Tests Equipment Schematic
Sulfuric acid
mist generator
-------
Compressed
air in
Modified 2000 ml
Erlenmeyer Flask
Figure 10. Modified Mist Generator
19
-------
TO
8
o
0)
N
U
•H
-P
Test Date
9/20/76
9/22/76
10/8/76
10/22/76
10/25/76
10/29/76
Open symbols - tests with
original
generator
Solid symbols- tests with
modified
generator
5 10 20 30 40 50 60 70 80 90
Percent of H2SC>4 below size indicated
95
98 99
Figure 11. Results of H2SO4 Mist Sizing Tests
-------
than 0.36 micron. In light of this information, the Andersen Impactor has
insufficient sensitivity to be used to size automotive sulfates. If it is
desired to generate and measure sulfuric acid mist below 0.36 micron range,
then additional development is needed on the sulfate mist generator and a
different method for measuring the mist size is needed.
This test series also showed that it is extremely hard to rid the im-
pactor plates of all residual sulfates. The time and care used to reduce
the residual level of the plates for this study would be inappropriate for
routine testing. For routine testing, to have sufficient sulfates deposited
on the plates to make the usual residual level insignificant, either the amount
of sulfuric acid put into the tunnel must be larger than can be generated by
the mist generator used or the injection time must be extended to several hours.
C. Sulfate Recovery Tests
The determination of sulfate recovery was done using the mist generator
and the PDP-CVS sulfate sample probe and filter hardware. For these tests,
the tunnel was heated to 53 to 57°C (128 to 135°F). The recovery tests are
summarized in Table 1. The average recovery was 105 percent, with a maximum
recovery of 120.8 percent and a minimum of 90.5 percent.
TABLE 1. SULFATE RECOVERY FROM MIST INJECTION TESTS
Test Date
10/18/76
10/18/76
10/19/76
10/26/76
10/27/76
11/3/76
Average
Tunnel
Temp. °C
53
54
53
57
57
56
Test
No.
1
2
1
1
1
1
Amount of
H2SO4 Injected, mg
49.0
71.1
76.0
64.9
33.1
60.0*
Percent H2SO4
Recovered on Filter
119.0
94.5
120.8
101.6
103.6
90.5
Average Recovery 105.0
Std. Dev. 12.5
Coeff. of Var. 11.9
* sulfate BCA procedure used to determine amount of mist injected
The average amount of sulfate lost on the probe during the first three
recovery tests was determined by washing the probe after the 10/19/76 test,
(thethird test),with 40 ml of 60 percent IPA and processing the solution using
the BCA sulfate procedure. The amount of sulfate on the probe(in terms of
yg/£ of sample flow)was divided by the total sulfate(in yg/& of sample flow)
from the first three tests to obtain the average percent probe loss. The
probe loss for these tests averaged 3.2 percent.
21
-------
Some of the spread in the recovery test data is felt to be due to the
accuracy of the titration procedure for determining the amount of sulfuric
acid injected into the tunnel. Due to the small amount of sulfuric acid
injected into the tunnel, a difference of 0.005 in the determination of the
normality of either the fresh solution injected or the remaining solution
(plus washing) could make a difference on the order of 15 percentage points
in recovery. The difference of 0.005 in normality translates to approximately
0.25 ml of titrant in the titration procedure. While the amount of titrant
can be read to 0.1 ml, the repeatability is normally around ± 0.2 ml. To
overcome this problem, a procedure was developed to use the BCA method to
determine the amount of sulfuric acid injected.
The procedure is to collect the residual acid and washing, then dilute
to 1000 ml total solution with distilled water. Next, a 40 ml aliquot of the
solution is diluted to 100 ml with 100 percent isopropyl alcohol. This solu-
tion is then processed by the sulfate filter BCA procedure using sulfuric acid
standards.
Sulfuric acid mist recovery tests using the CFV-CVS sampling system
were not run, since it was felt that the pressing need was for tests with
actual automotive exhaust to investigate the high total sampling system los-
ses reported by other laboratories.^) Thus work on the mist injection sys-
tem was concluded with the results considered satisfactory for the experiments
conducted. However, more development of these procedures is necessary before
they could be used as a system verification test.
D. Tunnel Propane Traverse
A traverse of the tunnel was also performed while injecting propane
into the tunnel. The results of the traverse are shown in Figure 12. There
is a slight stratification from top to bottom, but it is felt that it is not
large enough to affect the accuracy of the sulfate sample. The minimum and
maximum concentrations were within approximately ± 5 percent of the average.
-------
O 12/2/76 Traverse
to
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Inches from bottom of tunnel
Figure 12. Tunnel Traverse During Propane Injection
Top
-------
IV. TESTS WITH AUTOMOTIVE EXHAUST
This section describes the test vehicle, procedure, and test results
from sulfate tunnel tests using actual car exhaust.
A. Test Equipment and Procedure
The tests described in this section were performed using the 21 cm dia-
meter tunnel described in Section II. All tests described in this section
used the sample probe designed for use with PDP-CVS systems. That is, the
sample probe tip did not have a choked flow section. A CVS flow rate of
approximately 9.2 m3/min (325 cfm) and a sample flow rate of 0.023 m3/min
(0.8 cfm) was used during these tests.
The test car used to generate the exhaust sulfates was a 1975 AMC Hornet
Sportabout with a 4.98 litre (304 CID) V8 engine. This car was tested ex-
tensively for sulfate emissions under Contract 68-03-2118 and Task 2 of this
project's Task Order Contract. The car is equipped with a pelleted catalyst
and catalyst air injection system. It is known to be a higher than average
sulfate producer. The fuel used was a commercially available unleaded fuel
with the sulfur level adjusted to 0.04 weight percent using thiophene.
Two driving schedules were used. The first was a 64 kph (40 mph) constant
speed cycle. This cycle was chosen as a condition which would produce ade-
quate sulfates, yet would not cause undue strain on the engine, tires or dyna-
mometer. The second cycle was the SET-7 sulfate cycle, or as it is currently
called, the Congested Freeway Driving Schedule (CFDS). This cycle is a
variable speed cycle with two stops and an average speed of 56.0 kph (34.8 mph).
The test is 23.3 minutes long. The distance driven during the test is approx-
imately 21.7 km (13.5 miles).
B. Initial Probe Loss Tests
While preparations were being made to begin comparison testing between the
new tunnel and the EPA standard tunnel using actual car exhaust, the EPA Pro-
ject Officer requested that some probe loss tests be run with actual car ex-
haust on the new tunnel. These tests were felt necessary since a General
Motors study had indicated that there were considerable probe losses using a
nominal 350 CFM CVS and a small (approximately 21 cm ) tunnel. (8)
The tests conducted are listed in Table 2. The results of the first
series of tests are shown in Table 3 under Test Series A. This test series
shows that probe losses apparently can be large and seem to be at least par-
tially dependent on the amount of sulfate drawn through the probe. The per-
cent of total sulfate on the probe from Test Series A as a function of the
amount of sulfate recovered (filter plus probe) is shown in Figure 13. For
the three SET-7 tests, it appears that as the amount of sulfate put through
the probe increased, the percent of sulfate on the probe decreased. Note that
the tunnel temperature range for these tests was from 60°C to 100°C (140 to
212°F) with average temperature approximately 85°C (185°F).
In an effort to identify if the sulfate on the probe might be the
24
-------
TABLE 2. SULFATE PROBE LOSS TESTS
Date
Probe
Type of Test
1. Test Series A
12/7-8/76 1" s.s. SET-7
12/16/76 1" s.s. SET-7
12/30/76 1" s.s. SO2 injection
1/7-10/77 1" s.s. SET-7
2. Test Series B
1/17/77
1/19/77
1/19/77
3. Test Series C
1/26/77
1/27/77
1/28/77
3/8" s.s. SET-7
1/4" glass SET-7
1" teflon SET-7
1" teflon 40 mph (155°F tunnel)
1" teflon 40 mph (185°F tunnel)
1" teflon 40 mph (197°F tunnel)
No. of
Tests
10
2
1
12
1
1
Emissions Measured
H2SO4 and gaseous (4 tests)
H2SO4 and gaseous (1 test)
H2SO4 and S02
H2SO4 and gaseous (4 tests)
3 H2S04
3 H2S04
3 H2SO4
H2S04
H2S04
H2S04
Note: A 9.2 m3/min (325 cfm) PDP-CVS was used for all tests.
25
-------
TABLE 3. RESULTS OF PROBE LOSS TESTS
Avg.
Tunnel
Date Temp°C
Test Series A
12/7-8/76
12/16/76
12/30/76 (S02 inj.)
1/7-10/77
Test Series B
1/17/77 (3/8" s.s.)
1/19/77 (1/4" glass)
1/19/77 (1" Teflon)
Test Series C
1/26/77
1/27/77
1/28/77
85
85
50
85
85
85
85
68
85
92
No. of
Filters
10
2
1
12
3
3
3
1
1
1
Sum of Percent of
SO4= on SO4= on Total Total 804=
Filters, yg Probe, yg* SO^=, yg on Probe
5178 1575 6753 23.3
524 577 1101 52.4
>1 23
4257 1226 5483 22.3
700 426 1125 37.8
813 341 1154 29.6
1521 542 2063 26.3
1963 69 2032 3.4
2214 221 2435 9.1
1595 679 2274 29.9
Note that the results for each line represent the total aggregate sulfates
from a number of repetative tests.
*From single analysis at end of each set of repetative tests.
26
-------
70
1000 2000 3000 4000 5000 6000
Total Sulfate Passed Through Probe ~ yg
7000
8000
Figure 13. Percent Probe Loss Versus Sulfate Through Probe
27
-------
result of a reaction of the probe wall with sulfur dioxide, (SO2), a test
was run injecting pure SC>2 into the tunnel. The SC>2 was injected at a
rate approximately equal to exhaust SO2 during SET-7 test. This test was
run at a tunnel temperature of 50°C (122°F) which is close to the maximum
that can be obtained with the tunnel heaters without automotive exhaust
being put into the tunnel. The sulfate found on the filter was equivalent
to the usual background level. Sulfate above residual levels was found on
the probe. However, the sulfate level was less than a tenth of the sulfate
levels seen from the two previous probe loss tests run with car exhaust.
At the time the test was run, the results of the SC>2 injection test
were interpreted to mean that the probe sulfate did not come from a reaction
of the probe walls with SO2- Later tests with car exhaust showed the probe
losses to be a function of temperature as will be explained below. While no
tests with car exhaust were run at tunnel temperatures as low as 50°C, the
trend from Figure 15 indicates that probe losses with actual car exhaust
could be the same at 50°C as that seen from the S02 injection test. Thus it
is not certain how the results of the SC>2 injection test should be interpreted.
Therefore, SO2 injection tests over a range of tunnel temperatures are recom-
mended as a possibility for future investigations. One way to do this is to
use sulfur sterile fuel during tests with an actual car and inject SO2 into
the exhaust at the tunnel entrance.
A second series of tests was run to determine if probe material affected
the probe losses. This series of tests is listed in Tables 2 and 3 as Test
Series B. In this series, three consecutive SET-7 tests using the 1975 Hornet
were run with each of three types of probes. These tests indicate that while
probe material did have an effect on probe losses, substantial losses can
occur using stainless steel, glass and Teflon probes at tunnel temperatures
of 85°C (185°F). The 9.5 mm (3/8 inch) stainless steel probe had the highest
losses, 37.8 percent, and the 2.54 cm (1 inch) Teflon lined probe the smallest
losses, 26.3 percent.
Three tests were run at different tunnel temperatures to investigate the
effect of temperature on probe losses. The test series is listed in Tables 2
and 3 as Test Series C. Each test consisted of a 64 ]qph steady state run
for one-half hour using the 1975 Hornet. These tests show that tunnel tem-
perature does affect probe losses, with the probe losses increasing from 3.4
percent at 68°C (155°F) to 29.9 percent at 92°C (197°F).
C. System Sulfate Losses as a Function of Temperature
The initial series of tests showed that substantial probe losses can
occur with stainless steel, glass and Teflon probes and that the probe losses
were a function of the amount of sulfate passed through the probe and the tun-
nel temperature. Since there was such a large difference in the probe loss
between 85°C (185°F) and 92°C (197°F), it was felt by both EPA and SwRI that
further testing was necessary to verify the shape of the probe loss curve with
temperature. This test series is listed in Table 4.
A series of six tests were run using the 1975 Hornet as a source of exhaust
28
-------
TABLE 4. TUNNEL TEMPERATURE EFFECTS TEST SCHEDULE
Tunnel
Test
1
2
3
4
5
6
Temp. , °C
68
77
85
88
91
96
Test Condition
1/2
1/2
1/2
1/2
1/2
1/2
hr
hr
hr
hr
hr
hr
at
at
at
at
at
at
40
40
40
40
40
40
mph
mph
mph
mph
mph
mph
Probe
1" s.s.
1" s.s.
1" s.s.
1" s.s.
1" s.s.
1" s.s.
Emissions
S04,
S04,
S04,
S04,
S04,
S04,
S02,
S02,
S02,
S02,
S02,
S02,
Measured
gaseous
gaseous
gaseous
gaseous
gaseous
gaseous
Note: Both the probe and the tunnel were washed
with 60 percent IPA following each test.
TABLE 5. SUMMARY OF SYSTEM SULFATE LOSSES
Sulfate Losses,
Test
1
2
3
4
5
6
Filter
S04=
jig/m?
3052.61
3002.47
2496.82
2673.02
2843.57
2457.98
Probe
59.32
72.03
175.85
264.12
271.89
548.38
Tunnel
52.36*
57.66
67.97
101.69
116.14
129.84
ug/m3 @
Elbow
12.08
9.04
5.12
5.76
8.16
6.71
9.20 m/min. CVS Flow Rate
0.46 m.
Flex
pipe
28.60
29.59
39.09
29.03
31.78
30.90
Tunnel
+ elbow
+ flex
92.94
96.29
112.18
136.48
156.08
167.45
Total
losses
152.26
168.32
288.03
400.60
427.97
715.83
Total
Sulfates
jug/m
3204.87
3170.79
2784.96
3073.80
3271.54
3173.73
Tunnel
Temp
°C
68
77
85
88
91
96
Percent of Total Sulfate
1
2
3
4
5
6
95.39
94.67
89.65
86.97
86.92
77.45
1.85
2.27
6.31
8.59
8.31
17.28
1.63
1.82
2.44
3.31
3.55
4.09
0.38
0.29
0.18
0.19
0.25
0.21
0.79
0.93
1.40
0.94
0.97
0.97
2.80
3.04
4.02
4.44
4.77
5.27
4.65
5.31
10.33
13.03
13.08
22.55
68
77
85
88
91
96
*estimate from curve of tunnel temperature vs sulfate loss
29
-------
sulfate to determine the sulfate losses in the sampling system with changes
in tunnel temperature. A Teflon lined probe was used during these tests.
Each test consisted of a 25 minute run at 40 mph. An initial acceleration
from idle to 40 mph was part of each test. At the conclusion of the test,
the sulfate level in the sample probe and in all system components upstream
of the probe was determined.
Table 5 lists the sulfate on the filters together with the sulfate found
on each of the elements of the sample system. In the top half of the table,
the sulfate levels are expressed in micrograms per actual cubic meter of
dilute exhaust flow. The bottom part of the table shows the sulfate levels
as a percent of the total sulfate. As can be seen from the table, the probe
and tunnel losses increase as the tunnel temperature increases. The flexible
tubing connector losses measured for each test are constant, as would be expected,
at about 1 percent of the total sulfate. Figures 14 and 15 show the percent probe
and tunnel losses as a function of tunnel temperature. Figure 16 shows the total
sulfate losses (probe, tunnel, elbow, and flex) as a function of tunnel tempera-
ture.
It should be noted that these results are from one set of tests on a
particular car. It may be that the sampling system losses are also a function
of the sulfate concentration. Since the car used on this project has much
higher than average sulfate emissions, the sulfate losses shown here may not
be typical.
Remember also that the probe loss tests covered in the previous
section seem to indicate that a stainless steel probe would give somewhat
higher losses than a Teflon probe. Those tests also indicated that there is
a "seasoning" effect on the sampling system and that the losses could go down
considerably after a certain number of tests if the system was not washed
after every test. Thus while a considerable amount has been learned about
the sulfate sampling system losses, there are still many areas where more
information is needed.
D. Effect of Connecting Tubing Length
The various laboratories engaged in automotive sulfate sampling use dif-
ferent lengths of flexible exhaust tubing to connect the car exhaust system
to the sulfate tunnel. One of the items of investigation in this study was to
evaluate the effects of this connecting tubing length on sulfate losses. Two
different lengths of 10.2 cm (4 inch) diameter tubing were used, a 0.61 m
(2 foot) length and a 4.6 m (15 foot) length.
Several tests, each 25 minutes in length, at 64 kph (40 mph) steady state
were run with each length of connecting tubing. The test results are sum-
marized in Table 6. For these tests, probe and tunnel losses taken from
Figures 14 and 15 were used together with the sample filter sulfate value from
each test to obtain the total sulfate level.
As can be seen from the table, the sulfate losses in the connecting tubing
increased considerably as the tubing length increased. For the 0.61 m (2 foot)
length, the loss was 0.6 percent and for the 4.6 m (15 foot) length, the loss
was 20.4 percent.
30
-------
0)
c
c
3
EH
0
-P
c
0)
u
•I —
60
70 80 90
Tunnel Temp. Deg. C
100
110
Figure 14. Percent SO4~ on Tunnel Versus Tunnel Temperature
20
0)
ft
o
c
o
-------
6
0)
-p
CO
H1
-H
O
-P
10
O
CO
id
4J
O
O
-P
£
0)
O
60
70 80 90
Tunnel Temp. Deg. C
100
110
Figure 16. Percent SO4~ Lost on Sulfate Sampling System
Versus Tunnel Temperature
32
-------
TABLE 6. EFFECTS OF CONNECTING TUBING LENGTH
Test
Date
3/31/77
4/13/77
3/31/77
4/13/77
4/15/77
Vehicle
Flexible Exhaust
Pipe Length Temp °C
0.61 m (2 ft) 263
0.61 m (2 ft)
4.6 m (15 ft) 254
4.6 m (15 ft)
4.6 m (15 ft)
Exhaust
temp into
Tunnel °C
224
163
Tunnel
Temp °C
66.7
66.7
49.4
53.9
66.7*
Percent of
total 804 on
flex pipe
0.63
0.51
Avg 0.57
20.0
23.4
17.8
Avg 20.4
Total
S04
mg/km
37.59
40.15
42.54
38.20
41.87
*Tunnel dilution air preheated to maintain tunnel temperature
33
-------
V. SYSTEM MODIFICATIONS
As a result of the testing explained in the previous sections of this
report as well as some additional tests reported in this section, some system
modifications were required. This section explains the rationale for those
changes.
A. Critical Flow Sample Rate Evaluation
A series of tests were conducted to check out the components of the sulfate
sampling system designed for use with a CFV-CVS. Recall that a critical flow
section in the sampling system is required for the CFV-CVS and that the probe
entrance nozzle was chosen as the location for this critical flow (choked) section.
For choked flow the static pressure at the nozzle throat must be 0.528 of the
nozzle inlet static pressure. Although some pressure is recovered in the di-
verging section of the nozzle, to insure choked flow it was planned to keep the
pressure downstream of the nozzle at approximately 0.5 of the nozzle inlet pressure.
Since the pressure drop across the filter is large, it was recognized from the
start that a sample pump with high vacuum capability would be needed.
Prior to obtaining a pump, the nozzle was calibrated using ambient air.
The calibration curve is shown in Figure 17. The pressure loss curve for a
clean 0.5 micron Fluoropore filter was also determined and is presented in
Figure 18. If a tunnel pressure of approximately 735 mm of mercury is assumed,
then from Figure 17 and 18 it can be determined that a sample pump capable of
0.028 standard m /min (1 scfm) flow at 636 mm (25.0 inches) of mercury vacuum
is required. After a considerable search, a pump was located with this capability.
The pump is a Cask Model 2565. The manufacturers published flow ratings are shown
in curve form in Figure 19.
A SET-7 test was run with the CFV-CFS sample probe using a car known to
be a high sulfate producer (on the order of 50 mg/km). As the filter loaded
during the test, its pressure losses increased. At approximately 1100 sec-
onds into the test, the pressure loss became sufficient that the nozzle un-
choked. The flow continued to drop for the remainder of the test. From this
test it was concluded that 0.028 m /min (1.0 cfm) sample rate was too large
to maintain choked flow with a 47 mm, 0.5 Urn Fluoropore filter. After discussing
the problem with the Project Officer, it was decided to set the sample flow at
0.014 m /min (0.5 cfm).
.01
B. Methods to Reduce Tunnel Temperature
The tests discussed in the previous section demonstrated that sulfate
losses on the probe and tunnel increase as the tunnel temperature increased.
This section briefly examines two methods of lowering the sulfate tunnel
temperature and presents the modification made to arrive at the final tun-
nel configuration. However, since the elevated tunnel temperature is caused
by the hot vehicle exhaust gas, it was first necessary to determine what tem-
perature should be used as exhaust gas temperature in a system design.
34
-------
n
•O
C
(B
U
CN
+J
id
3
C
•H
n
tc
cu
i
(0
3
+J
FM
-------
least squares straight line
Y = 0.00110 + (7.8307 x 10~5)(X)
r2 = 0.997
•d
G
a
u
-p
id
c
I
n
6
8
0.030
0.025
0.020
0.015
0.010
0.005
0.000
i—r
' ' L." '-
3^
&"
^
*r.-".
Snp7
fe
••(.-
t i L
- -I—f-
••I'--'
r
50
100
150
200
250
300
350
Differential pressure, mm Hg
(p upstream = 743 mm HgA)
Figure 18. Pressure Drop Across Clean 47 mm FlUoropore Filter
36
-------
0.6
0.5
0.4
•d
0.2
0.1
:1^
;-,l,.--l
100
200
300
400
500
600
700
800
Inlet Vacuum, mm Hg gage
Figure 19. Capacity Curve for Cast 2565 Pump
37
-------
The exhaust gas temperature of three different catalyst cars were meas-
ured during dynamometer operation. Table 7 shows the maximum exhaust tem-
perature obtained on these cars.
While this is certainly not a large sample, it does show that exhaust
temperatures on the order of 380°C (716°F) are possible during the SET-7.
It is probable that other vehicles could have higher exhaust temperatures.
Nevertheless, for this analysis, 380°C was used for a design exhaust gas
temperature.
TABLE 7. MAXIMUM EXHAUST TEMPERATURE DURING
DYNAMOMETER OPERATION FOR THREE CARS
Car
1
1
2
3
Mfgr.
Ford, LTD
Ford, LTD
Chevrolet
Hornet
Engine
Size, liters
5.75
5.75
5.74
4.98
Inertia, kg
2268
2268
2041
1587
Cycle
Type
FTP
FET
SET-7
SET-7
Max. Exhaust
Temp. °C
285
350
378
356
1. Cooling Dilution Air
One method for lowering the tunnel temperature is to cool the dilu-
tion air. For a simple air conditioning system, the cooling limit for the
dilution air should be about 4°C (39°F) to prevent ice formation on the coils.
Assuming 24°C (75°F) room air, this is about a 20°C (36°F) drop in dilution
air temperature. Cooling the dilution air to 4°C results in a tunnel tem-
perature drop of about 14°C (26°F) using a nominal 9.20 m3/min (325 CFM) CVS
with a blower inlet cooled to 43°C (110°F) and a 5.74 liter (350 CID) engine
with exhaust temperature of 380°C (716°F). If it is desired to keep the tun-
nel below 77°C (170°F), this amount of cooling would not be sufficient for a
5.74 liter engine in a 2041 kg car -
With a more complex cooling system, the air could be cooled to lower
temperatures. Using the example 5.74 liter car from above, a dilution air
temperature of about -35°C (-32°F) is required to lower the peak tunnel tem-
perature to 77°C (170°F). This low temperature could also cause problems with
condensation.
The above examples assume a CVS with a heat exchanger to maintain the
blower inlet temperature at about 43°C (110°F). If a CFV-CVS without a heat
exchanger is used, more cooling would be required since as the tunnel tempera-
ture increases, mass flow through the CFV-CVS decreases, causing the tunnel
temperature to rise. Also, sophisticated temperature control is required due
to the rapidly changing exhaust temperature and flow rate.
38.
-------
2. Increase Amount of Dilution Air
Another method for lowering the tunnel temperature is to increase the
CVS capacity, thus increasing the dilution air flow. Using the 5.74 liter car
from the example above, a CVS with approximately 17.0 m^/min (600 CFM) capacity
would be required to lower the peak tunnel temperature to 77°C (170°F) . A CFV-
CVS without a heat exchanger would have to be somewhat larger, on the order of
18.5 m-^/min (650 CFM) for reasons explained above.
C. Final System Modification Chosen
After considering all the factors involved, it was decided by the EPA
Task Officer that the small (21 cm) tunnel should be used together with a
larger CVS. It was requested that the sampling system nozzle be sized for
525 cfm CVS flow and 0.5 cfm sample flow. The new nozzles were made and a
series of three tests run on the completed sulfate sampling system with the
critical flow nozzle and a 520 CFM CVS. The tests run are described in Table
8. The results are shown in Table 9.
From the Table 9, it is evident that the increased flow rate reduced
the sulfate losses on the tunnel walls. The sulfate losses in the flexible
connecting tubing were slightly higher than seen in previous tests with lower
CVS flow, while the losses in the exhaust entrance elbow were about the same.
The sulfate losses in critical flow sample probe were considerably higher than
seen in tests with the noncritical flow probe and lower CVS flows .
The probe losses of 15 and 22 percent from the tests 1 and 2, with average
temperatures of 69°C (156°F) and 74°C (165°F) respectively, are higher than
desired for routine sulfate testing. For the noncritical flow probe at tem-
peratures below 77°C, the probe losses were less than 3 percent. While time
did not permit further investigation of the sulfate losses with the critical
flow probe, it is recommended that a thorough investigation of the losses
with this probe be conducted prior to using this system for routine sulfate
testing.
39
-------
TABLE 8. TEST SCHEDULE WITH LARGE CVS
Test No.
Test Type
Duration (min)
1 64 kph steady 30
2 SET-7 23,
3 SET-7 23,
For All Tests
Notes: 1. CVS flow 14.7 m^/min (520 cfm)
2. critical flow nozzle used on probe
3. sample flow = 0.014 m3/min (0.5 cfm)
heater condition
Max heat
Max heat
Min. temp controlled
to 43°C (110°F)
TABLE 9. RESULTS FROM TESTS WITH LARGE CVS
Sulfate Losses yg/m"
Test
No.
1
2
3
Test
Type
64 kph
SET-7
SET-7
Average
Tunnel
Temp. °C
69
74
59
Filter
Sulfate
yg/m3
1624.82
2077.29
1902.15
CFV
Probe
307.80
615.45
125.67
Tunnel
10.76
9.60
3.64
Percent of
Test
No.
1
2
3
Test
Type
64 kph
SET-7
SET-7
Tunnel
Temp. °C
69
74
59
Filter
81.16
74.85
91,14
CFV
Probe
15,38
22.18
6.02
Tunnel
0.54
0.35
0.17
Elbow
7.20
12.86
12.43
Total Sulfate
Elbow
0.36
0.46
0.60
Flex
Pipe
51.23
60.13
43.15
Flex
Pipe
2.56
2.17
2,07
Total
Losses
376.99
698.04
184.89
Total
Losses
18.84
25.16
8.86
Total
Sul fates
yg/m3
2001.81
2775.33
2087.04
-------
LIST OF REFERENCES
1. Bradow, R. L. and Moran, J. B., "Sulfate Emissions from Catalyst
Cars, a Review." SAE Paper No. 750090, February 1975.
2. Ingalls, M. N. and Springer, K. J., "Measurement of Sulfate and
Sulfur Dioxide in Automotive Exhaust." EPA Report No. EPA-460/3-
76-015, August 1976.
3. Somers,J. H., et al, "Automotive Sulfate Emissions - A Baseline
Study." SAE Paper No. 770166, February 1977.
4. Dietzmann, H. E., "Protocol to Characterize Gaseous Emissions as
a Function of Fuel and Additives Composition." EPA Report No. EPA-
600/2-75-048, September, 1975.
5. Shapiro, A. H., "The Dynamics and Thermodynamics of Compressible
Fluid Flow." Vol. 1, Chapter 4, The Ronald Press Co., N.Y., N.Y.,
1953.
6. Bradow, R. L. , Carpenter, D. A., Klosterman, D., Black, F. M., and
Tejada, S., "Sulfate Emissions from Catalyst and Non-Catalyst Cars."
SAE Paper No. 740528, October, 1974.
7. Wilson, W. E., et al, "General Motors Sulfate Dispersion Experiment:
Summary of EPA Measurements." Journal of the Air Pollution Control
Association, Vol. 27, No. 1, January, 1977.
8. Letter from C.J. Elder, Environmental Activites Staff, General Motors
Corporation, to Richard Lawrence, Emission Control Technology Division,
EPA, Ann Arbor, Michigan, dated October 26, 1976.
41
-------
APPENDIX A
STATEMENT OF WORK
-------
EXHIBIT A
REVISED 2-13-76
STATEMENT OF WORK
The purpose of this task is to provide EPA with a dilution tunnel
and sampling system compatible with the critical flow venturi CVS units
used in certification testing.
1. Design and build a dilution tunnel and sampling system which
will meet the following requirements:
(a) Provide mixing of the exhaust and dilution air.
(b) Be compatible with a CVS flow rate of 325 SCFM.
A typical dilution tunnel operating conditions will be
735 mm Hg. A and 150F.
(c) Be compatible with EPA certification test cells, as
determined by discussions with, project officer or other
persons designated by project officer.
2. Design parameters such as dilution tunnel length, diameter,
material and configuration; mixing orifice diameter; probe location,
material and size; and sampling train components and configuration will
be determined by discussion with the task officer and others, as appropriate.
These parameters should be chosen within the first 10 days of the task
period.
3. Two planning meetings have been held in Ann Arbor and the
following parameters have been tentatively agreed upon:
£
(a) The dilution tunnel diameter will be approximately^
8 inches,
(b) The distance between the exhaust inlet and the probe
tip will be 8 pipe diameters.
(c) The distance between the probe tip and the downstream end
of the tunnel will be two pipe diameters.
(d) The tunnel material will be stainless steel.
(e) A mixing orifice will be located at the plane of the
exhaust inlet«
(f) The probe will be made of stainless steel tubing.
(g) The filter holder will be outside the tunnel
4. Design and build a sampling system compatible with critical
flow venturi CVS units. Flow velocity into the probe shall be within +
10% of the velocity of the dilute exhaust mixture adjacent to the probe
at all times. Sampling through a critical flow venturi or other means
such as electronic control can be used to accomplish the desired flow
control.
5. Design and build an apparatus which will inject a known amount
of sulfuric acid aerosol into the-..dilution tunnel. Dilution tunnel and
analytical system verification can be performed using this apparatus in
much the same way a propane injection is currently used for CVS
A-2
-------
2
of
.ification. The size of the aerosol should be measured and 98%.should
* less than one micron aerodynamic diameter. It is recog-
nized that the development work specified in this item will not necessarily
result in a good sulfuric acid mass injection system. A "best effort"
Ls expected. Problem areas should be identified so that subsequent
investigations can address them.
6. Validate the tunnel and sampling system by running the following
tests:
(a) Sulfuric acid injection using the apparatus developed
in 5, above, if possible.
(b) Continuously inject propane while performing radial
traverses with a probe in the vicinity of the sulfate
probe location* Record HC concentration continuously.
Traverses in 2 radial directions should be performed.
Plot: HC concentration versus radial distance. Determine
the difference between the average observed HC concen-
tration and the expected value.
, ^
7.* Compare the new tunnel at approximately 300 SCFM with the 18"
tunnel (on hand at SwRI) at 475 to 600 SCFM by:
(a) Alternating vehicle exhaust from a vehicle at .s_teady_
jrrijise_conditions between the two systems. Approximately
20 samples (H2 S04 + S02 + gaseous emissions) will be
taken in each configuration. Since a CFV-CVS is not
available at SwRIf a standard PDP-CVS can be used with
the new tunnel, however the new CFV compatible sample
system should be used for these steady state tests.
During the 300 CFM tests both the CFV sampling system and
a standard probe should be operated in parallel. Sulfuric
acid level and probe losses determined with each system
can then be compared,,
(b) Running consecutive suLfate_cy.c\e?f alternating the
vehicle exhaust from one system to the other. Approximately
six cycle*with each tunnel will be required. A standard
probe and sampling system may be required i-f a PDP-CVS is
used instead of a CFVCVS.
Determine probe and funnel losses with each system. A single determination
for all tests run in each tunnel infeach of parts (a) and (b) above is
sufficient. Continuously record the temperature of the sample entering
the filter holder. Note that the CFV sampler is designed for 325 SCFM
but that operation at the low end of the normal CVS range, i.e. 300
SCFM, is requested here. This should not cause a problem since these
two flows are within 10% of each other, which is the range allowed in
item 4, above.
A-3
-------
8. Determine the effect of the length of connecting tubing from
vehicle to tunnel (tubing specifications to be supplied by EPA).
Record temperature of exhaust gas at vehicle tailpipe and dilution
tunnel inlet using both short (2s) and long ( 15') lengths of tubing.
Measure sulfuric acid trapped in the connecting tubing. The following
method, or equivalents should be used.
(a) Rin-se the tubing with a 60/40 IPA solution until
an analysis of the IPA shows little or no sulfate response
on the barium chloranilate (BACL) analytical system.
(b) Run one or more emission tests (S7).
(c) Rinse the tubing with IPA and analyze the rinse solution
for sulfate.
9. * Determine the effect of dilution air humidity by running S-7
tests at three dilution air humidity levels of 100 tollO, 70 to 80, and
20 to 40 grains/pound^ Measure probe losses and size distribution of
the collected particulate.
10. Deliver the dilution tunnel and sampling system to EPA in Ann
Arbor, Michigan. Provide technical assistance in setting up and checking
out the ccnplete system with a CFV-CVS. For planning purposes qn estimate
of 1 man for 3 days at the Ann Arbor facility is reasonable.
11. Provide 3 complete sets of shop drawings and specifications,
•including one reproducible set.
12. Other.
(a) The sulfate analytical system should be dedicated
to this test work so that preliminary results are obtained
as quickly as possible i.e. within a few hours. This is
the only way the number of tests to be run can be determined
while testing is in progress.
(b) The number of tests requested above, are only esti-
mates. Close liaison with the Task Officer is required
to insure that adequate testing is performed and that
unnecessary testing is avoided.
(c) In the event probe or tunnel losses are found, system
modification and additional testing will be done as
agreed upon at that time between the contractor and the
task officer.
A-4
-------
13. Provide additional equipment to complete sampling system
including rotometer, dry gas meter, filter, sampling pump,
and alarm system to indicate loss of critical flow.
14. Provide mobile cabinet to house above components and install
components to provide complete working system.
15. Calibrate dry gas meter and verify that complete system is
operational
16. Provide dilution air filter and heater assembly similar to
assembly in use for tunnel validation tests performed during
Nov - Dec, 1976.
* Items 7 and 9 were deleted in.favor of increased testing on item 12(c)
A-5
-------
APPENDIX B
VELOCITY TRAVERSE OF 21 cm DIAMETER TUNNEL
-------
SOUTHWEST RESEARCH INSTITUTE SHEET NO—!_OF_!
DATA SHEET PROJECT
SUR.IFP.T 21 CM. D/A. TUNHEL, QATg 1 \ / 2G 174
SORg T£ftN/g£SE BY M.Kl. JL,
•SHEETS
®
CO- BOTTOM)
i
1 4-
L 2"
1
; r 3*
i A'1
\ — 1
;."H*
"Ij"
_L
i
._)_
_._.ToP
: i
STJvnc
PRESS.
1,05
4.0^
l.lfe.
4.2D
4.JO.
4. iO
4. jo
:
TOTAL
-L.
4, Lo
" 4", 1 5
^^5
..4.50
4.I5
4- i?
4, IS
0\f?i PRESS.
O.D5
i
0 , 06
O, 01
.. 0./0
^p , o5
0, 05
0,05
VELOC IT/"
,«
1
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1 1 •? /-^
(I 4. U
wo
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VELOCITY
AIR \ti-ociTt FLPU) CHARTS IM
,
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-------
Top
CD
3
§
H
M-l
05
I
M
Bottom
800 900 1000 1100 1200
Air Velocity, feet/second
FIGURE B-l. TUNNEL VELOCITY PROFILE
1300
B-3
-------
Comparison of Measured Average Velocity
and Average Velocity from Volume Flow Calibration
(Area of Tunnel = 0.385 ft2)
1. CVS blower flow at 28.0 in. Hg.A and 70°F = 381.7 ACFM from blower
calibration curve
2. Volume flow at tunnel condition (29.1 in. Hg.A and 71°F) during
traverse.
VT = 381-7 x Mir x §5- = 368 ACFM
3. Average velocity = 368 = 956 ft/min
0.385
4. From velocity profile curve intergrated average velocity is 1009
ft/min. This is only 5.4 percent higher than average velocity from
volume flow, which is considered good agreement. Part of the dif-
ference is undoubtedly because 890 ft/second was taken as the velocity
all the way to the wall (were the velocity is in reality zero) since
the velocity profile was not obtained close to the wall.
5. Maximum velocity = X Average velocity = 1.25 X average velocity
6. If volume flow average is used, and maximum velocity is taken to be
1.25 times average velocity, then the design velocity for the sulfate
probe is 1195 ft/m (956 x 1.25), since the probe is to be in the area
of maximum velocity.
B-4
-------
APPENDIX C
MIST GENERATOR CALIBRATION DATA
-------
APPENDIX C - MIST GENERATOR CALIBRATION DATA
Test I - Determination of Mist as a Percent of Total H2SO4 Input
Run
1
2
3
4
5
Test
Time
7'0"
6'43"
10 '39"
7' 57"
7 '05"
Total ml
in Generator
25
25
25
25
25
Mist
Ml
2
2
3
3
3
Percent
Mist
8.0
8.0
12.0
12.0
12.0
Air
Press (psi)
24
20
40
30
25
Test II - Optimization of Compressed Air Pressure
Run
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Test
Time (sec)
140
19.8
17.7
19.0
21.0
24.0
31.0
20.0
20.0
17.0
16.5
16.5
17.0
17.5
Total
ml
into Generator
1 ml
It
11
II
ri
it
ii
ii
ii
ii
ii
ii
IT
II
Air
Press, (psi)
0
30
20
30
35
40
10
15
16
18
20
22
24
26
C-2
------- |