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.
The Experiments: Thermal
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