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Impact Dynamics of Newtonian and Non-Newtonian Fluid Droplets on Super Hydrophobic Substrate

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Impact Dynamics of Newtonian and Non-Newtonian Fluid Droplets on Super Hydrophobic Substrate IMPACT DYNAMICS OF NEWTONIAN AND NON-NEWTONIAN FLUID DROPLETS ON SUPER HYDROPHOBIC SUBSTRATE A Thesis Presented By Yingjie Li to The Department of Mechanical and Industrial Engineering in partial fulfillment of the requirements for the degree of Master of Science in the field of Mechanical Engineering Northeastern University Boston, Massachusetts December 2016 Copyright (©) 2016 by Yingjie Li All rights reserved. Reproduction in whole or in part in any form requires the prior written permission of Yingjie Li or designated representatives. ACKNOWLEDGEMENTS I hereby would like to appreciate my advisors Professors Kai-tak Wan and Mohammad E. Taslim for their support, guidance and encouragement throughout the process of the research. In addition, I want to thank Mr. Xiao Huang for his generous help and continued advices for my thesis and experiments. Thanks also go to Mr. Scott Julien and Mr, Kaizhen Zhang for their invaluable discussions and suggestions for this work. Last but not least, I want to thank my parents for supporting my life from China. Without their love, I am not able to complete my thesis. TABLE OF CONTENTS DROPLETS OF NEWTONIAN AND NON-NEWTONIAN FLUIDS IMPACTING SUPER HYDROPHBIC SURFACE .......................................................................... i ACKNOWLEDGEMENTS ...................................................................................... iii 1. INTRODUCTION .................................................................................................. 9 1.1 Motivation ......................................................................................................... 10 1.2 Characteristic outcomes from a droplet impact on solid surface ............. 11 1.3 Super hydrophobic surface ............................................................................ 12 1.4 Related theories ............................................................................................... 14 2. Experiments ...................................................................................................... 19 2.1 Experimental apparatus ........................................................................................ 19 2.2 Preparation of super hydrophobic surface ........................................................ 27 2.3 Droplet generation ................................................................................................. 29 2.4 Experimental procedures ..................................................................................... 31 2.5 Surface tension measurement ............................................................................. 37 3. Results and discussion ................................................................................... 38 3.1 Definition ................................................................................................................ 38 3.2 Droplet impact behaviors ..................................................................................... 45 3.3 Weber number and impact behavior ................................................................... 61 3.4 Viscosity and Spreading ....................................................................................... 67 4. Conclusion ........................................................................................................ 73 5. Suggestions and Future work ........................................................................ 73 REFERENCES ....................................................................................................... 74 Appendix ............................................................................................................... 78 LIST OF FIGURES Figure 1 : Examples of characteristic outcomes from a water droplet impact on solid surface . .................................................................................................................12 Figure 2: Sketch of a hydrophobic surface and hydrophilic surface ...............................13 Figure 3: Water droplet with 150° contact angle ............................................................13 Figure 4: Viscosity of Newtonian, Shear Thinning and Shear Thickening fluids as a function of shear rate .............................................................................................14 Figure 5: Experimental apparatus schematic illustration ...............................................21 Figure 5a: High speed camera ......................................................................................22 Figure 5b: Light source, RPS CoolLED 100 Studio Light RS-5610 ...............................23 Figure 5c: Rainin pipette ...............................................................................................24 Figure 5d: Conduct chamber. .......................................................................................25 Figure 5e: Tokina optical lens. ......................................................................................26 Figure 6: : Self assembled monolayer made of HDFT molecules ..................................27 Figure 7: Illustration of droplet generation .....................................................................30 Figure 8: Illustration of a micropipette positioning .........................................................33 Figure 9: Camera setting at pre-focusing stage ............................................................34 Figure 10: Camera setting at experiment stage ...........................................................35 Figure 11: Illustration of record button ..........................................................................36 Figure 12: Sketch of experiment camera locations ......................................................36 Figure 13: Pendant drop schematic ..............................................................................37 Figure 14: Illustration of pendant droplet method measurement ...................................38 Figure 15: Spreading stage of a water droplet impact on a solid surface ......................39 Figure 16: Recoiling stage of a water droplet impact on a solid surface ........................40 Figure 17: Rebound stage of a water droplet impact on a solid surface ........................40 Figure 18: Illustration of contact diameter .....................................................................41 Figure 19: Illustration of rim, spire, film and capillary waves .........................................42 Figure 20: Illustration of jet ...........................................................................................43 Figure 21: Illustration of smooth rim ..............................................................................43 Figure 22: Illustration of fragmentation ..........................................................................44 Figure 23: A water droplet with D =2.6mm and v =1.45 m/s impacted on a super hydrophobic surface ..............................................................................................46 Figure 24: A milk droplet with D =2.75mm and v =1.91 m/s impacted on a super hydrophobic surface ..............................................................................................49 Figure 25: A 5% corn starch droplet with D =3.41mm and v =1.72 m/s impacted on a super hydrophobic surface .....................................................................................52 Figure 26: A 5% corn starch droplet with D =3.40mm and v =1.71 m/s impacted on a super hydrophobic surface .....................................................................................55 Figure 27: A blood droplet with D =2.93mm and v =1.81m/s impacted on a super hydrophobic surface ..............................................................................................57 Figure 28: A blood droplet with D =3.28m and v =1.72m/s impacted on a super hydrophobic surface ..............................................................................................59 Figure 29: Spires number K vs impact velocity v of water droplet with volume 1(3.6mm±0.1mm) and volume 2(2.6mm±0.2mm) ..................................................62 Figure 30: Spires number K vs impact velocity of milk droplet with volume 1(3.4±0.16mm) and volume 2(2.5±0.15mm) ..........................................................62 Figure 31: Spires number K vs impact velocity of 5% corn starch solution droplet with volume 1(3.4±0.13mm) and volume 2(2.5±0.22mm) ..............................................63 Figure 32: Spire number K vs velocity of 15% corn starch solution with volume 1(3.3±0.18mm) and volume 2(2.4±0.18mm) ..........................................................63 Figure 33: Spire number K vs velocity of rabbit blood with volume 1(3.3±0.2mm) and volume 2(2.97±0.13mm) .......................................................................................64 Figure 34: Spire number K vs velocity of 1:1 diluted blood with volume 1(3.25±0.1mm) and volume2 (2.78±0.2mm) ...................................................................................64 Figure 35: K vs Weber number of all experimental fluids ..............................................66 Figure 36: Illustration of pinched section and bulging section .......................................67 Figure 37: Schematic of hypothetical droplet evolution with time variation ....................69 Figure 38: Time variation of spread factor .....................................................................69 Figure 39: Impact
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