Surface Tension Impelled Lowgravity Liquid Mixing A Research Project Proposal for the NASA Reduced G

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Surface Tension Impelled Low-gravity Liquid
MixingA Research Project Proposal forthe NASA
Reduced Gravity Student Flight Opportunities
Program

• Paul Gosling
• Sara Marten
• Yo-Rhin Rhim

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Presentation Overview

• Surface Tension and Wetting
• Microgravity Research
• The STILLMix Project
• Experimentation and Theory
• The Proposal Process

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The STILLMix Team

• Group of seven juniors and seniors at JHU
• Mowry Cook Junior, Eng. Mech. and Physics
• Paul Gosling Senior, Physics
• Sara Marten Junior, Mechanical Engineering
• Paul Nerenberg Junior, Physics
• Sam Phillips Junior, Civil Engineering
• Yo-Rhin Rhim Senior, Mechanical Engineering
• Mike Sharma Junior, Mechanical Engineering

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Surface Tension and Wetting
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The Study of Surface Tension Effects

• Since the 19th century, physicists and mechanical
  engineers have been studying surface tension and
  wetting effects.
• Knowledge of these phenomena is interesting as an
  academic pursuit, and also for its usefulness in
  practice.
• Applications of wetting and surface tension
  effects include but are not limited to
• The invention of detergents
• Understanding heat transfer through boiling
• Dispersal of insecticides on plants
• Movement of blood in veins

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People

• Pioneering work on terrestrial studies of liquid
  spreading on surfaces was done by
• Thomas Young (1773-1829)
• Pierre-Simon Laplace (1749-1827)
• And in the last few decades has been continued
  by
• P.G. de Gennes
• Van P. Carey
• P.C. Wayner, Jr. (also studied microgravity
  effects)
• And many others.

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Interfacial Surface TensionPredominant physical
property governing behavior of small volumes of
liquid
Image from http//gre.ac.uk/gg11/surfacetension.h
tml
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Components of Surface Tension
Any boundary between two phases has surface
tension. More generally, it is expressed in terms
of the difference in free energy per unit area
across a given interface. In our case, we
consider the free energies of the Solid-Liquid
(?SL ), Solid-Gas (?SG ), and Liquid-Gas (?LG )
boundaries
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Other Important Parameters(All coupled to
surface tension)

• Spreading coefficient (S)
• Defined as S ?SG - ?SL - ?LG
• Contact angle
• Density and viscosity of liquid
• Volume of liquid

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Wetting

• There are three basic types of liquid-solid
  system properties
• Complete wetting the liquid spreads across the
  surface without stopping (S gt 0)
• Partial wetting the liquid spreads to an
  equilibrium radius, stopping there and beading (S
  0)

• Non-wetting the liquid immediately beads up
  on the surface and does not spread at all
  (S lt 0)

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Microgravity Research
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Complications from the Presence of Gravity

• Gravity forces mask surface tension effects and
  make it difficult to study key wetting
  properties.
• Only recently has it become possible to eliminate
  gravity from studies of surface tension and
  wetting, and the STILLMix team hopes to be one of
  the first to study these effects under
  microgravity conditions.
• In gravity, buoyancy complicates mixing by
  causing variations in the vertical direction
  (stratification).

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The STILLMix Experiment

• Question - Can mixing be accomplished with
  surface tension as the only driving force?
• Objective - study the mechanics and dynamics of
  surface tension-driven mixing of two liquids in
  low gravity
• Method - observe boundary interactions and mixing
  of two liquids brought into contact by allowing
  them to wet the same surface in microgravity
  conditions

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Purpose

• Obtain visual data of liquid/liquid interactions
  in microgravity conditions
• Results intended to yield a better understanding
  of
• Surface tension driven spreading
• Microgravity mixing

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Applications

• Chemistry and biology experiments requiring
  microgravity conditions
• Waste recycling on the International Space
  Station and the Shuttle Transportation System
• Avoiding use of mechanical power to mix by
  implementing a passive mixing technique
• Casting of parts in a mold by polymerization of
  two mixed liquids useful for long space
  missions where unforeseen spare parts will be
  needed

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Methods of Achieving ?-Gravity

• Cheap and very accessible Drop Tower
• Moderately expensive and accessible by
  application NASA KC-135 Aircraft
• 10,000 per lb (exhorbitantly expensive) and
  accessible to very few Shuttle and ISS

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The KC-135 Vomit Comet Aircraft
The NASA KC-135 aircraft has been modified to
simulate microgravity conditions for periods as
long as 23 seconds by flying a repeating
parabolic trajectory, diving steeply downwards
each time.
Since 1959, NASA Johnson Space Center (JSC) has
been operating microgravity simulation aircraft.
The early versions were used for astronaut
training and research for the Mercury, Gemini and
Apollo programs. More recently the aircraft have
been made available to researchers and students
conducting microgravity experiments in all fields
of science, medicine and engineering.
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NASA Reduced Gravity Student Flight Opportunities
Program (RGSFOP)

• Gives undergraduate student groups an opportunity
  to perform experiments in a microgravity
  environment
• Experience involves
• Proposing
• Designing
• Fabricating
• Flying
• Evaluating Results
• Educational/Public Outreach Activities

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If We Get Accepted
(champagne glass)
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The STILLMix Project
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STILLMix Project Overview

• Mixing will take place on test surfaces with a
  surface structure pattern.
• Control series of experiments with smooth mixing
  surface will be run alongside for comparison.
• Mixing process will be recorded using a digital
  video camera.
• Images will be analyzed using image processing
  tools to understand the nature of mixing and the
  influence of the wavefronts shape.

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Experimental Procedure

• Two liquids will be injected onto a surface (some
  with surface structures, some smooth)
• Four liquid/liquid combinations will be used
• Water/water
• Water/glucose
• Water/ethyl alcohol
• Water/motor oil
• These liquids will wet the same surface and
  eventually come into contact with one another
• Teflon tape will be used along the perimeter of
  the viewing area to prevent wetting of entire
  test section
• This mixing process will be recorded using a
  digital video camera

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Test Section Schematics
Underside view of test surface
Cross-sectional view of individual test section
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Methodology

• A wetting liquid injected onto a surface will
  spread forming a circular pattern
• We propose that surface structures (such as
  grooves) can alter the shape of this flow
• This shape can then be optimized for more
  homogeneous mixing

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Surface Modification

• The surface will be modified (with grooves, as
  shown below, or by another means) so as to
  flatten the wavefront.
• If the grooves are too small, liquid will flow
  over them.
• Wider grooves will slow forward progress, as well
  as momentum resulting from injection, leaving
  surface tension as the primary driving force.

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Individual Test Section

• Syringes penetrating sidewalls sealed using
  O-rings
• Partitions separate individual test sections
• Test surface attached to sidewalls with aluminum
  L-brackets

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Experiment Rack

• Control and test columns (10 each) bolted to
  mounting plate
• Camera mount
• Test rack frame (to stabilize apparatus and
  attach it to aircraft floor)

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Data Retrieval and Analysis

• In-flight and ground experiments will be recorded
  with a digital video camera.
• Image color at different points on the test
  section will be analyzed in MATLab? to discern
  level of mixing.
• Liquid travel and mixing processes will be
  time-resolved and compared to behavior predicted
  by model.

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Safety Considerations

• Worst-case safety factor calculated to be
  approximately 3.5 for given acceleration loads (9
  gs forward, 3 gs aft, 6 gs down, 2 gs
  lateral, and 2 gs up)
• Possible hazards, precautions, and contingency
  plans detailed
• Proper handling/storage of semi-hazardous fluids
  (motor oil, ethyl alcohol) outlined

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Design Iterations

• Original design (using capillary action)
• Mixing between two plates
• No need for microgravity
• Revised to study surface mixing
• Momentum walls
• Syringes replace tubes as means of getting liquid
  onto surface
• Surface structures suggested as means of shaping
  liquid wavefront

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Experimentation and Theory
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Preliminary Terrestrial Experiments Mixing

• In this case, two water samples, dyed different
  colors, were allowed to wet the same surface. To
  drive the samples here we had to use gravity, as
  the system turned out to be non-wetting.

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Preliminary Terrestrial Experiments Spreading

• Drops of Water, Oil, Ethanol, and Glucose were
  deposited on a high-density polycarbonate surface
  and observed as they spread

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Observations and Obstacles

• The water, ethanol, and glucose beaded up on the
  surface.
• The oil spread, but slowly over a period of
  minutes.
• We need to do the experiments in a time period of
  23 seconds or less.
• To reduce spreading time, we need to make a
  completely wetting system by adding surfactants
  to the sample or using a new solid surface.
• For relevance of the results we decided to change
  the surface.

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Modifications

• For the next series of experiments we may use a
  different test section surface or a surfactant
  adsorbed to the current surface, solidified to
  form a new solid substrate.
• An appropriately chosen surface or surfactant
  should ensure complete wetting within the
  requisite 23 seconds.

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Theoretical Models of Spreading

• Liquid propagation is dependent on surface
  tension and wetting properties of system
• Precise phenomena acting at boundaries of a
  spreading droplet are unknown
• In spite of their importance, wetting
  processes are still poorly understood. On the
  theoretical side, 180 years after the pioneering
  work of Young and Laplace, a number of basic
  capillary problems are just beginning to be
  solved.
• P.G. de Gennes, Wetting Statics and Dynamics,
  Rev. Mod. Phys., Vol. 57, No. 3, Part 1, July 1985

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Empirical Models of SpreadingGravity Dominant

• In 1976, Lopez et al found experimentally, with
  gravity, the radius of a spreading droplet went
  as
• R(t) ?3/8 (? g t / ?)1/8
• where ? is the volume, ? is the density, g is
  the acceleration of gravity, and ? is the
  viscosity
• Lopez, J., Miller, C.A., Ruckenstein, E., J.
  Colloid Interface Sci. 56 (1976), 460

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Empirical Models of SpreadingSurface Tension
Dominant

• In 1985, De Gennes et al found, ignoring the
  effect of gravity, that the radius goes as
• R(t) ?3/10 (? t / ?)1/10
• where ? is the volume, ? is the surface tension,
  and ? is the viscosity
• P.G. de Gennes, Wetting Statics and Dynamics,
  Rev. Mod. Phys., Vol. 57, No. 3, Part 1, July
  1985

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The Proposal ProcessFlight Plans and Other
Aspects
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Pre-flight Operations

• Sample preparation
• Syringe loading and installation
• Test section preparation (cleaning)
• Sealing of partitioned test sections
• Thorough check of all seals
• Last minute adjustments

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In-flight Operations

• Ten tests of each liquid combination
• Five on control smooth surface, five testing
  chosen surface structure
• Mixing surfaces recorded by digital camera

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Post-flight Operations

• Unload apparatus
• Remove camera mount
• Unseal and open apparatus
• Cleaning procedures
• Retrieve and backup video images
• Store apparatus

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Surface Tension Impelled Low-gravity Liquid
Mixing OutReach and Education (STILLMORE)

• Outreach section of proposal worth 30 of overall
  score
• Four elements of STILLMORE
• Creation and maintenance of a project homepage
  (www.wse.jhu.edu/stillmix)
• Production of a project video
• Production of a final report
• Educational and professional talks, video
  distribution, and interactive activities

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Project Video

• Digital video camera will be used to produce team
  outreach video
• All phases, from design to conclusion, will be
  documented
• High quality editing and production will be done
  at the JHU Digital Media Center
• Completed video used as part of educational and
  professional talks

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Outreach Talks

• Educational
• Inspire interest in space science among younger
  students
• Participation of high school students in design
  aspect
• Work with the already established JHU Tutorial
  Project
• Professional
• Inform colleagues of research efforts
• Talks planned at the Baltimore sections of the
  American Institute of Aeronautics and
  Astronautics and the American Society of
  Mechanical Engineers

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Funding

• Budget total approximately 7,500.00
• Includes digital video camera, apparatus
  materials, other supplies, liquid samples, travel
  and lodging, shipping, and medical testing
  expenses
• Secured half funding from the Maryland Space
  Grant Consortium
• Other likely sources include the Whiting School
  of Engineering, the Krieger School of Arts and
  Sciences, and the national office of the Society
  of Physics Students

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Thank you Dr. Herman!