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Convection Experiment
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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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Update: June 2012
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