Please go down two posts for the original report on our first experiment -- thanks!
As mentioned in the post reporting the results of our initial microgravity tests, the Mark II Menticulator will require a more sophisticated method of deploying a nicely sized sphere of soda. My initial thought was to use a water balloon, but an afternoon of sweaty testing on the back porch lead to the discovery of several serious problems with this approach.
The first is that when the balloon ruptures, friction between the skin of the balloon and the water results in significant spray, some of which is clearly fast enough to overcome the surface tension of the water (and remember, the soda will have a lower surface tension because of the sweetener and other ingredients). If some of this spray coats the camera port, we may not be able to see the reaction. I did multiple tests with different balloon sizes and tensions, and even coated the inside of the balloon with oil, in an attempt to reduce the spray, with no real change in the results.
But an even more serious problem is that unless the balloon is under a significant amount of tension, it will either not puncture at all, or the puncture will not propagate! If this happens in flight, we will experience a total menticulation failure and the entire experiment will be ruined.
So it was back to the drawing board (I have an ACME drawing board, the same brand Wile E. Coyote uses). I had to come up with a method of simply and smoothly deploying the soda. When I'm faced with a problem like this, I like to sit in the workshop and idly play with the various parts and tools that I have available. What I'm looking for is relationships between things that will spark a connection. After a while, this idea came to me.
The initial idea was to use a balloon inside the soda bottle to force the soda out of the bottle and up a tube into the apparatus. I already had the tube -- the Geysertube that Steve Spangler sent to me earlier in the year. I drilled out a hole in it so I could insert some plastic tubing, inserted a bit of copper tubing into the end of the tubing to stiffen it, ziptied a balloon onto the end, and stuck the other end into a hiking bota-bag, which acts as the bellows. A little hot-glue and tape sealed everything up.
Squeeze the bag, the balloon inflates, and liquid is forced up the tube in a reasonably controlled manner (this test had a leak, thus the bubbles).
Okay, so now I've got a basic method of deploying the soda sphere. The next thing to work on is, once I have the sphere deployed, how do I test the convection hypothesis in a manner that leaves no room for doubt about the results, and is as simple and foolproof (always a plus when I'm involved) as possible.
I'm also looking for a more precise method of pumping up the balloon than the bota bag (which was just the cheapest thing I could find that would work reasonably well). Something like a really, really big industrial syringe (500-1000ml!) would be perfect, but I haven't been able to find one yet -- if you know of something that might work, in particular something that's effectively self-locking, so after I get the bubble to the right size, I can just let go and the balloon will stay its current size, let me know!
Subsequent to these experiments, the blog got slashdotted, and I started getting lots of suggestions. One that I'm definitely going to follow up on in the near future is a modification of Ger's suggestion about a box of cola; my current thinking is to build a thin enclosure that will confine the convective flow pretty much to two dimensions.