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Question:
I am a Project manager of Exhibits with Museum of Science anbd d Industry in Tampa FL. I am trying to develop a hands on demonstration of Unbreakable and work well in daylight. Our idea was to have a dish of liquid which would react to heat applied to the bottom and would show the flow caused by the heat . We have not been able to find the mixture we need .. any help will be appreciated. mike



Replies:
Hi Mike:
I would suggest something very viscous like glycerin. I have used it for a number of fluids experiments because it is nontoxic. With moderate heating you should be in an interesting regime of what is called Benard Convection. There was a Scientific American article on this some time ago (early eighties or something like that). You might also check through an index for the Amateur Scientist section of that journal. These flows can be modeled by using a dimensionless number called the Rayleigh Number (named after Lord Rayleigh, the famous British Physicist). The number can be written in terms of a heat flux (heating rate per unit surface area). Reference to this number can be found in many textbooks on Heat Transfer. The one that I suggest is called, Fundamentals of Heat and Mass Transfer by F.P. Incropera and D.P. DeWitt. It should be available in the library. You might also check with Edmund Scientific. They (I believe) sell liquid crystal solutions that change color with temperature If you chose the correct liquid crystal or maybe by adjusting the heating rate, you could generate temperatures in a range that the liquid crystals would change color. This could be a very pleasing visual experience.
Nice project! Good Luck!

Dr. Dave


Your message was a little garbled so I am not completely sure what your question was, it has something to do with heat flow. For a very inexpensive demonstration have you considered a lava lamp? This could be used as a demonstration of both convection currents (fluid movement) and radioactive/conductive heat loss. Sounds like a fun job! gregory r bradburn


If I understand the objective of Mike's request, one could very neatly demonstrate convection with a small sprinkle of dark colored sawdust in a beaker of water. Dump in the sawdust, stir it around, and then heat the beaker at its edge with a Bunsen burner. In a short time, one can observe the round and round cycling of sawdust particles -- rising on the warm side, moving across the surface. and descending on the cooler side. Works well so long as the water doesn't boil.

Once the concept is implemented, it shouldn't be hard to redesign it using a large closed loop of glass tubing and a heat lamp as the source of heat to keep things going.

Regards,

ProfHoff



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