Hydrodynamical Analysis of Nanometric Aluminum/Teflon Deflagrations BY SHAWN C. STACY, B.S.M.E. A THESIS IN MECHANICAL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN MECHANICAL ENGINEERING Approved Michelle Pantoya Chairperson of the Committee Valery Levitas Brandon Weeks Accepted Fred Hartmeister Dean of the Graduate School May 2008 Texas Tech University, Shawn C. Stacy, May 2008 Acknowledgments I am exceptionally grateful to everyone that has helped me accomplish so much while at Texas Tech University. Specifically, I’m thankful for the opportunities and guidance of Dr. Michelle Pantoya has given me over the last two years. With her help, I have grown much as a researcher and I am more prepared for any challenges ahead of me. I would also like to thank Dr. Mark Grimson at the Texas Tech Imaging Center for helping me with the finer points of electron microscopy. Also, I would like to acknowledge Idaho National Laboratory for technical and financial assistance that was critical to this work. ii Texas Tech University, Shawn C. Stacy, May 2008 Table of Contents ACKNOWLEDGMENTS ................................................................................... II TABLE OF CONTENTS ................................................................................... III ABSTRACT .......................................................................................................... V LIST OF TABLES .............................................................................................. VI LIST OF FIGURES .......................................................................................... VII I. INTRODUCTION AND BACKGROUND ..................................................... 1 1.1 OVERVIEW ................................................................................................. 1 1.2 ALUMINUM COMPOSITE REACTIVE MATERIALS ............................. 1 1.3 NANO-SCALE COMPOSITES.................................................................... 3 1.4 UNDERWATER TESTING ......................................................................... 5 1.4.1 SEQUENCE FOR UNDERWATER REACTIONS ................................. 5 1.4.2 UNDERWATER TESTING ..................................................................... 8 II. EXPERIMENTAL SETUP AND PROCEDURE ....................................... 11 2.1 SAMPLE PREPARATION ......................................................................... 11 2.2 EXPERIMENTAL SETUP ......................................................................... 14 2.3 DATA ACQUISITION ............................................................................... 16 2.4 REAL CODE CALCULATIONS ............................................................... 20 III. RESULTS ...................................................................................................... 23 3.1 GAS GENERATION .................................................................................. 23 3.2 PRESSURE ................................................................................................. 26 3.3 OBSERVATIONS ...................................................................................... 27 iii Texas Tech University, Shawn C. Stacy, May 2008 3.4 TMD RESULTS .......................................................................................... 29 IV. DISCUSSION ................................................................................................ 33 4.1 UNDERWATER TESTING OF DEFLAGRATIONS ............................... 33 4.2 HYDROPHOBIC TEFLON ........................................................................ 35 4.3 GAS GENERATION .................................................................................. 37 V. CONCLUSIONS ............................................................................................ 43 VI. FUTURE WORK.......................................................................................... 44 REFERENCES .................................................................................................... 55 APPENDIX .......................................................................................................... 58 iv Texas Tech University, Shawn C. Stacy, May 2008 Abstract The hydrodynamics of deflagrations from reactive materials (RM) submerged underwater can be studied using a modified aquarium test. Normally loose powder RM will disperse after being submerged in water. Introducing hydrophobic materials such as Teflon into the reactant matrix, enables a barrier against permeation of water into the reactants. Also, ignition via resistance heating can be difficult underwater because significant energy is lost by convection off the wire into the water. Nano-Al particles require significantly less energy for ignition than their micron scale counterparts such that underwater ignition via resistance heating can be achieved. The objective of this study is to examine the reaction hydrodynamics from a submerged nano Al-Teflon mixture as a function of mixture composition and bulk density. Submerged Aluminum/Teflon mixtures were ignited and the ensuing reaction was recorded with a high speed camera and a pressure transducer. The resulting bubble shape, size, and pressure histories along with the burn time and rate allow the analysis and comparison of different fuel/oxidizer compositions and powder packing densities. Results show that as the density of the powder decreases the reaction transitions from a slow jet of multiple bubbles to quick single bubble. One observation is that as the percentage of aluminum increases the bubble radius also increases even though there is less of the gas producing Teflon in the mixture. This could imply that the excess aluminum is reacting with water. v Texas Tech University, Shawn C. Stacy, May 2008 List of Tables 1. POWDER SPECIFICATIONS.......................................................................... 12 2. ACTUAL MASS PERCENTS OF AL AND TEFLON FOR MIXTURES ... 13 3. REAL CODE RESULTS FOR INCREASING PRESSURE .......................... 14 4. EXPERIMENTAL RESULTS ........................................................................... 23 5. PERCENT TMD AND BUBBLE SHAPE RESULTS ..................................... 30 6. REAL CODE RESULTS FOR TEFLON AND 80% PURE ALUMINUM .. 50 7. REAL CODE VOLUME PRODUCT RESULTS FOR AL + TEFLON WITH A MASS PERCENTAGE OF WATER ............................................................ 50 8. REAL CODE ADIABATIC FLAME TEMPERATURE RESULTS FOR AL + TEFLON WITH A MASS PERCENTAGE OF WATER ........................... 61 9. EXPERIMENTAL RESULTS FOR DISPLACEMENT ENERGY, BUBBLE GROWTH RATE, AND PRESSURIZATION RATE .................................... 62 10. PERCENT OF WATER REQUIRED FOR COMPARISON IN REAL CODE RESULTS ................................................................................................ 63 vi Texas Tech University, Shawn C. Stacy, May 2008 List of Figures 1. HEAT OF COMBUSTION COMPARISON OF AL/TEFLON, TNT, AND THERMITE MIXTURES CALCULATED USING REAL CODE ................. 2 2. UNDERWATER EXPLOSIVE BEHAVIOR .................................................... 8 3. SEM MICROGRAPH OF ALUMINUM AND TEFLON AT 50% TMD. ... 12 4. TANK SETUP INCLUDING THE SAMPLE BLOCK (A), IGNITION WIRE LEADS (B), AND UNDERWATER BLAST PRESSURE SENSOR (C). ........................................................................................................................ 16 5. OVERALL TEST SETUP WITH THE HIGH SPEED CAMERA, TANK, AND FIBER OPTIC LIGHT GUIDE ............................................................... 17 6. EXAMPLE OF A SINGLE BUBBLE REACTION WITH 14 MILLISECONDS BETWEEN EACH FRAME .............................................. 17 7. LIGHTED CONDITIONS WITH THE HIGH SPEED CAMERA (A), TANK SETUP (B), FIBER OPTIC LIGHT GUIDE (C), AND VARIAC TRANSFORMER (D) ......................................................................................... 18 8. PHANTOM SOFTWARE FOR RADIUS ANALYSIS. .................................. 19 9. THE RADIUS IS OBTAINED FROM TWO POINTS PER FRAME ON THE SURFACE OF THE BUBBLE. THE POINTS ARE AVERAGED FOR THE FINAL RADIUS CURVE. ........................................................................ 20 10. MAXIMUM RADIUS DATA FROM HIGH SPEED VIDEOS SHOWING THE MAXIMUM RADIUS INCREASES WITH POWDER EQUIVALENCE RATIO. .................................................................................. 25 11. MAXIMUM BUBBLE VOLUME ..................................................................... 26 12. A REPRESENTATIVE PRESSURE PROFILE FOR ONE SECOND ........ 27 13. EXPERIMENTAL PRESSURE RESULTS AT MAXIMUM RADIUS ....... 27 14. EXAMPLES OF UNBURNED MICRON ALUMINUM AND TEFLON REACTIONS ....................................................................................................... 28 vii Texas Tech University, Shawn C. Stacy, May 2008 15. ILLUSTRATION SHOWING THE INFLUENCE OF CARBON ON BUBBLE TRANSPARENCY ............................................................................ 29 16. AIR BUBBLE BEFORE REACTION .............................................................. 29 17. %TMD AND BURN TIME ANALYSIS .......................................................... 30 18. FROM LEFT TO RIGHT: THE JET OF BUBBLES, THE BALL OF BUBBLES, THE MUSHROOM SHAPED BUBBLE, AND FINALLY THE SINGLE BUBBLE THAT IS USED FOR THE RADIUS ANALYSIS. ........ 31 19. RADIUS OSCILLATIONS FOR BLOCK RIGHT1......................................