The Experiments
MFMG-Isothermal
The goals of the experiment were:
1) To determine if a stream of honey injected into water would exhibit the Rayleigh-Tomotika
instability and break into small drops [30, 31].
2) To determine if an aspherical drop of water in honey would spontaneously assume
a spherical shape.
To eliminate bubles, Dr. Foale improvised a centrifuge.
Fig. 3 Filling the syringe with honey. All fluids had to be contained and so
we developed cumbersome procedures using zip-lock bags. Mike Foale balked at
our procedures and developed this one. No honey escaped the MWA. The markings
on the straw are separated by 1 cm.
The syringe into which fluid was injected was strapped down in the Microgravity
Working Area.
Four runs were performed by Dr. Michael Foale during Increment 8.
Run 1: a stream of pure honey was injected into pure water.
Dr. Foale injected the honey stream but air bubbles also appeared. Some movement
of the stream was observed, although it is difficult to see this in Fig. 5.
The bubbles also moved, which suggest residual acceleration caused the flow.
However,
it is clear that the stream did not exhibit the Rayleigh-Tomotika instability.
Fig. 5. Top: A stream of pure honey injected into water.
Run 2: a stream of diluted honey was injected into pure water.
Some honey was diluted to approximately 20% in water and injected into pure
water. It was not possible to observe the stream because of the poor contrast
between
the honey and the water.
Run 3: a blob of pure water (with food coloring) was injected into diluted
honey.
Dyed water was injected into an approximately 20% honey-water mixture. The
intent was to create a blob of water and see if it would spontaneously become
spherical.
The injection was not smooth, and the water was distributed more than was desired.
Also, bubbles were present. Fig. 6 shows that the shape of the water did not
significantly change but some of the bubbles moved toward the “top” of
the image. Several explanations are possible: The residual g vector had changed
so that the bubbles was just ‘floating up”. It could be that Marangoni
convection caused by the honey – water concentration gradient propelled
the bubbles. Or it may be that some effective interfacial convection occurred,
although this seems unlikely given that the shape of the water did not change
except near the inlet. At that point the concave water region became slightly
less concave. However, the motion of the bubbles is synchronized with this
water motion and so probably buoyancy-driven convection was at work.
Time lapse movie of dyed water being injected into 80:20 honey:water. Total time is 10 minutes.
Time lapse movie of dyed water being injected into pure honey. Total time is 10 minutes.
To dramatically illustrate why the experiments had to be performed in weightlessness, view a movie of honey being poured into water under 1 g in real time.
After a week of experiments, Dr. Foale held an audio conference with the PI, Pojman.