UNCLASSIFIED SCANNING ELECTRON MICROSCOPE STUDIES ON AGGREGATION CHARACTERISTICS OF ALUMINA NANOFLUIDS INTERIM REPORT TFLRF No. 443 by Nigil S. Jeyashekar, Ph.D., P.E. U.S. Army TARDEC Fuels and Lubricants Research Facility Southwest Research Institute ® (SwRI ® ) San Antonio, TX for Bridget L. Dwornick, Allen S. Comfort, and Dr. James S. Dusenbury U.S. Army TARDEC Force Projection Technologies Warren, Michigan Contract No. W56HZV-09-C-0100 (WD17–Task 4) UNCLASSIFIED: Distribution Statement A. Approved for public release August 2013 ADA UNCLASSIFIED
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UNCLASSIFIED
SCANNING ELECTRON MICROSCOPE STUDIES ON AGGREGATION CHARACTERISTICS OF ALUMINA
NANOFLUIDS
INTERIM REPORT TFLRF No. 443
by Nigil S. Jeyashekar, Ph.D., P.E.
U.S. Army TARDEC Fuels and Lubricants Research Facility Southwest Research Institute® (SwRI®)
San Antonio, TX
for Bridget L. Dwornick, Allen S. Comfort, and
Dr. James S. Dusenbury U.S. Army TARDEC
Force Projection Technologies Warren, Michigan
Contract No. W56HZV-09-C-0100 (WD17–Task 4)
UNCLASSIFIED: Distribution Statement A. Approved for public release
August 2013
ADA
UNCLASSIFIED
UNCLASSIFIED
Disclaimers Reference herein to any specific commercial company, product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the Department of the Army (DoA). The opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or the DoA, and shall not be used for advertising or product endorsement purposes.
Contracted Author As the author(s) is(are) not a Government employee(s), this document was only reviewed for export controls, and improper Army association or emblem usage considerations. All other legal considerations are the responsibility of the author and his/her/their employer(s).
DTIC Availability Notice Qualified requestors may obtain copies of this report from the Defense Technical Information Center, Attn: DTIC-OCC, 8725 John J. Kingman Road, Suite 0944, Fort Belvoir, Virginia 22060-6218.
Disposition Instructions Destroy this report when no longer needed. Do not return it to the originator.
UNCLASSIFIED
UNCLASSIFIED
UNCLASSIFIED
SCANNING ELECTRON MICROSCOPE STUDIES ON AGGREGATION CHARACTERISTICS OF ALUMINA
NANOFLUIDS
INTERIM REPORT TFLRF No. 443
by
Nigil S. Jeyashekar, Ph.D., P.E.
U.S. Army TARDEC Fuels and Lubricants Research Facility Southwest Research Institute
® (SwRI
®)
San Antonio, TX
for
Bridget L. Dwornick, Allen S. Comfort, and Dr. James S. Dusenbury
UNCLASSIFIED: Distribution Statement A. Approved for public release
August 2013
Approved by: Gary B. Bessee, Director U.S. Army TARDEC Fuels and Lubricants
Research Facility (SwRI®)
UNCLASSIFIED
REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188
Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) 27-08-2013
2. REPORT TYPE Interim Report
3. DATES COVERED (From - To) June 2011 – December 2013
4. TITLE AND SUBTITLE Scanning Electron Microscope Studies on Aggregation Characteristics of Alumina Nanofluids
5a. CONTRACT NUMBER W56HZV-09-C-0100
5b. GRANT NUMBER
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) Jeyashekar, Nigil
5d. PROJECT NUMBER SwRI 08.14734.17.401
5e. TASK NUMBER WD 17 (Task 4)
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER
U.S. Army TARDEC Fuels and Lubricants Research Facility (SwRI®) Southwest Research Institute® P.O. Drawer 28510 San Antonio, TX 78228-0510
U.S. Army RDECOM U.S. Army TARDEC 11. SPONSOR/MONITOR’S REPORT Force Projection Technologies NUMBER(S) Warren, MI 48397-5000 12. DISTRIBUTION / AVAILABILITY STATEMENT UNCLASSIFIED: Dist A Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES
14. ABSTRACT This research study establishes the relationship between sonication parameters and overall particle volume fraction in the base fluid, to the volume fraction of nanoparticles in the aggregate cluster and overall thermal conductivity enhancement of the nanofluid. The test matrix includes two power levels, with five overall particle volume fractions at each power level, and five sonication times for each overall particle volume fraction. The research concludes that sonication time has negligible effect on cluster size and number of particles per aggregate cluster at a constant overall particle volume fraction and vice versa. The research also concludes that nanofluid with higher thermal conductivity can be obtained when cluster size is limited to 200 nm. It is recommended that future research should emphasize on particle modification, such as encapsulation, to optimize and achieve an aggregate cluster size limit of 200 nm. 15. SUBJECT TERMS Aggregates, Clusters, Nanofluid, Nanoparticle, Scanning Electron Microscope, Sonication, Thermal Conductivity 16. SECURITY CLASSIFICATION OF: 17. LIMITATION
OF ABSTRACT 18. NUMBER OF PAGES
19a. NAME OF RESPONSIBLE PERSON NIGIL SATISH JEYASHEKAR
a. REPORT Unclassified
b. ABSTRACT Unclassified
c. THIS PAGE Unclassified
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19b. TELEPHONE NUMBER (include area code)
210-522-2533
Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18
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EXECUTIVE SUMMARY
Nanofluids are prepared by dispersing nanoparticles in base fluid using a sonicator for a fixed
period of time and at a fixed power level, thereby imparting a specific energy density to the
nanofluid. Extensive literature review on thermal conductivity enhancement in nanofluids does
not reference a standardized procedure for preparing nanofluids. The time period for sonication
and power level varies among peer reviewed literature and its relationship to nanoparticle
aggregation characteristics and overall nanofluid thermal conductivity has not been determined.
The current research work fills this technical void by determining the effect of sonication time
and overall nanoparticle volume fraction on aggregation characteristics of nanoparticles in a base
fluid. The two aggregation parameters investigated are cluster size and volume fraction of
nanoparticles in a single aggregate cluster. Furthermore, determining the thermal conductivity of
the aggregates as a function of cluster size establishes a limit on the maximum size limit on
clusters in a nanofluid in order to achieve high thermal conductivity.
The research work is accomplished by obtaining the aforementioned aggregation parameters
from a matrix of nanofluid samples containing alumina nanoparticles (40 nm nominal diameter)
dispersed in deionized water. The matrix includes two sonication power levels (70 W and
100 W). At each power level, the matrix contains five nanofluid samples with overall volume
fractions ranging from 1% to 5%. Five samples are taken at each volume fraction and sonicated
for five different sonication times. The sonication times for 70 W ranges from 20 minutes to
80 minutes, whereas for 100 W, the sonication time ranges from 14 minutes to 56 minutes. The
test matrix is designed such that the energy density imparted to the nanofluid samples at both
power levels are the same. Such a test matrix design enables comparison of the effects of
sonication time and overall volume fraction on aggregation characteristics at two different power
levels. The nanofluid samples are then placed on a carbon grid for image acquisition using
Scanning Electron Microscope (SEM). The resulting image is analyzed using Clemex Vision
PE® image analysis tool to obtain particle size distribution and fractal dimension. This data is
further processed to obtain the number of nanoparticles and volume fraction of nanoparticles in a
single aggregate cluster.
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The cluster size distribution and the number of particles per cluster in the alumina nanofluid have
been characterized as a function of sonication time and overall nanoparticles volume fraction at
two different power levels. It has been concluded that at both power levels, sonication time has
negligible effect on the cluster size and the number of particles per cluster when the overall
volume fraction is a constant and vice versa. The smaller clusters that contain larger fraction of
particles compared to the base fluid will have a higher thermal conductivity compared to larger
clusters with fewer particles and a large volume fraction of the base fluid. It has been concluded
that the overall thermal conductivity enhancement can be maximized by limiting the cluster size
to a hydraulic mean diameter less than 200 nm. The thermal conductivity of the clusters are
marginally higher than the base fluid and remains almost a constant for all clusters with size
greater than 200 nm.
The results from this research has established the fact that optimizing the cluster distribution to
yield nanofluids with superior thermal characteristics cannot be solely achieved by sonication
parameters, such as time or power level. It is recommended that future work should emphasize
on other methods to optimize aggregate cluster size, such as surface modification of
nanoparticles by encapsulation, prior to dispersion in the base fluid and hence, study its effect on
overall thermal conductivity of the nanofluid.
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FOREWORD/ACKNOWLEDGMENTS
The U.S. Army TARDEC Fuel and Lubricants Research Facility (TFLRF) located at Southwest
Research Institute (SwRI), San Antonio, Texas, performed this work during the period June 2011
through December 2013 under Contract No. W56HZV-09-C-0100. The U.S. Army
Tank Automotive RD&E Center, Force Projection Technologies, Warren, Michigan
administered the project. Mr. Eric Sattler (RDTA-SIE-ES-FPT) served as the TARDEC
Mr. Allen Comfort, and Dr. Jay Dusenbury of TARDEC served as project technical monitors.
The authors would like to acknowledge the contribution of the TFLRF technical support staff,
the University of Texas at San Antonio along with the administrative and report-processing
support provided by Dianna Barrera.
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TABLE OF CONTENTS
Section Page
EXECUTIVE SUMMARY .............................................................................................................v FOREWORD/ACKNOWLEDGMENTS ..................................................................................... vii LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES ....................................................................................................................... ix ACRONYMS AND ABBREVIATIONS ........................................................................................x 1.0 INTRODUCTION AND OBJECTIVE ..................................................................................1 2.0 THEORY: ACOUSTIC CAVITATION AND AGGLOMERATION ...................................2 3.0 PROJECT SCOPE ..................................................................................................................3 4.0 NANOFLUIDS PREPARATION AND TEST MATRIX .....................................................3 5.0 SEM IMAGE ACQUISITION ...............................................................................................4 6.0 IMAGE PROCESSING AND DATA EXTRACTION ..........................................................5
6.1 IMAGE CALIBRATION ......................................................................................................6 6.2 IMAGE PROCESSING AND MODIFICATION ........................................................................6 6.3 DATA EXTRACTION .........................................................................................................8 6.4 AGGREGATE SIZE DISTRIBUTION ANALYSIS ...................................................................8
7.0 RESULTS: ANALYSIS AND INFERENCE .........................................................................9 8.0 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK .........................12 9.0 REFERENCES .....................................................................................................................13 APPENDIX A. SEM Images of Alumina Nanofluids at Different Sonication times,
Volume Fractions and Sonication Power Levels ........................................... A-1
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LIST OF TABLES
Table Page
Table 1. Alumina Nanofluids Matrix ............................................................................................. 3 Table 2. Test Matrix for SEM Measurements ............................................................................... 4
LIST OF FIGURES
Figure Page
Figure 1. Hitachi S-500 Scanning Electron Microscope Instrument ............................................. 5 Figure 2. SEM Image of Alumina Nanofluid ................................................................................ 6 Figure 3. Intensity Histogram of SEM Image (in Figure 2) .......................................................... 7 Figure 4. SEM Image Modified for Data Extraction ..................................................................... 7 Figure 5. Volume Fraction of Nanoparticles in the Aggregate versus Cluster Diameter as
a function of sonication time at 70 W ..................................................................... 9 Figure 6. Volume Fraction of Nanoparticles in the Aggregate versus Cluster Diameter as
a function of Overall Volume Fraction of Alumina Nanoparticles at 70 W ......... 10 Figure 7. Volume Fraction of Nanoparticles in the Aggregate versus Cluster Diameter as
a function of sonication time at 100 W ................................................................. 11 Figure 8. Volume Fraction of Nanoparticles in the Aggregate versus Cluster Diameter as
a function of Overall Volume Fraction of Alumina Nanoparticles at 100 W ....... 11 Figure 9. Thermal Conductivity of Clusters at 100 W for all Sonication Times and
Overall Volume Fraction of Alumina Nanoparticles ............................................ 12 Figure A-1. ϕoverall = 1%, P = 70 W............................................................................................ A-2 Figure A-2. ϕoverall = 2%, P = 70 W............................................................................................ A-3 Figure A-3. ϕoverall = 3%, P = 70 W............................................................................................ A-4 Figure A-4. ϕoverall = 4%, P = 70 W............................................................................................ A-5 Figure A-5. ϕoverall = 5%, P = 70 W............................................................................................ A-6 Figure A-6. ϕoverall = 1%, P = 100 W.......................................................................................... A-7 Figure A-7. ϕoverall = 2%, P = 100 W.......................................................................................... A-8 Figure A-8. ϕoverall = 3%, P = 100 W.......................................................................................... A-9 Figure A-9. ϕoverall = 4%, P = 100 W........................................................................................ A-10 Figure A-10. ϕoverall = 5%, P = 100 W ..................................................................................... A-11
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ACRONYMS AND ABBREVIATIONS
% Percent
ϕint Volume fraction of nanoparticles in a single aggregate cluster
ϕoverall Overall volume fraction of nanoparticles in the base fluid
df Fractal dimension
DLS Dynamic Light Scattering
kcl Thermal Conductivity of Clusters in the Base Fluid
KJ Kilo Joule
KV Kilo Volt
m/s meter per second
mg milligram
min minute
ml milliliter
nm nanometer
Nint Number of alumina nanoparticles in a single aggregate cluster
rcl Radius of the cluster
rp Radius of the alumina nanoparticles (20 nm)
SEM Scanning Electron Microscope
SwRI Southwest Research Institute
TARDEC Tank Automotive Research, Development and Engineering Center
TFLRF U.S. Army TARDEC Fuels and Lubricants Research Facility