[Geysers] Re: Benchtop geysers

[Davis, Brian L.]

> About ten years ago my daughter and I built a remarkably successful
> geyser out of a 1000ml Erlenmeyer flask, a stout rubber stopper with
> a hole, and a section of copper tubing that exactly fit the hole.

That sounds ideal - especially the easily tunable nature of it. Getting a cheap hot plate of some sort at Target is another great idea I (embarrassingly) didn't think of. The hardest part was where to get a flask - I ended up begging in the chemistry department today, just to try out the idea. The result was a 500 ml flask with a 8 mm I.D. glass tube 1.2 meters long. This works pretty well, although I certainly mad a mess in the kitchen... and got the ceiling a little wet at times. With that setup, it went off about once every 2.5 minutes, jetting water about 6-8 inchs, with spray from a final "steam phase" hitting the ceiling about 4' overhead. I used a tupperware bowl with a hole poked in the bottom for a catch basin (didn't get the spray obviously), and the resulting "water hammer" as the pool was forced back into the tube was impressive to watch at the bottom (the flask almost instaly fills back up when the steam pressure collapses). Your method sounds better in many ways (cheaper, easier... I might even use PVC or some high-temperature variation for a more "durable" classroom demo), but the glass tube did give an interesting view - prior to an eruption it was obvious that pressure oscillations were building be watching the large bubbles filter slowly up the tube. Normally this was uniform... but as an eruption approached, they would irregularly move up and down as the pressure variations surged the column. This was much more obvious in the tube than in watching the surface waters.

> What was cool was how even modest variations in the tube affected the
> eruptions.

And I think your (in hindsight more obvious) way is a *great* way to go about that. Thanks!

> For instance, how far above the bottom of the flask do you have
> the end of the tube?  It mattered a great deal.

Agreed. I'm not sure if that's a good model for a natural geyser or not - I suspect it would depend on if the conduit is mostly vertical (so little or no trapped head space) or horizontal (places where you could build up a steam bubble, or get a vapor lock sort of situation).

> the best results were with the tube bent into two complete 360 degree
> vertical rings before going straight up.

How high was your setup (in other words, what was the maximum pressure head, and what was the volume of the tube relative to the heated reservoir)?

> One thing - there were inevitable leaks.

My wife sort of noticed that as I was dancing around the kitchen this evening :).

Tomorrow I'll probably try to instrument my bare-bones-basic setup, with a thermometer in the top "pool", a pressure sensor near the bottom, and a bubble detector to see what can be "seen" of boiling at depth. We'll see what I can get, but I really like your approach - thanks for kicking me in a new direction!

-- 
Brian "yes, dear, I'll clean up the floor when I'm done" Davis