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Building a convection model for plate tectonics and ocean currents Answered

I'm building a model to show our museum visitors how convection works related to plate tectonics.  (It can also be used for ocean currents.)  I'm stuck on the heating source, though, because we cannot have open flames.

The model is a cell of water, about 0.5" wide X 10" long X up to 8" high (depending on water depth).

I would to implement some type of circuit with a resistor that produces heat at the bottom, and inside the cell, and battery powered.  At the top at either end would be ice cubes, to cool the water so it falls back down and recirculates.  To see the currents, the ice cubes have blue food coloring, and I use a long pipette to inject coloring at the bottom near our current heat source, and mug of hot water.

I'm having trouble finding information on:
- what type of resistor (how many ohms?, anything specialized for being submerged?)
- how large a battery/ies for a 4-hour day on the floor (rechargeable, of course)
- other steps to prevent corrosion

It will need an on/off switch and a battery connector, too, of course...

I'm sure I may be missing some other important things to consider, too.

Any feedback would be great.




4 years ago

A simple, but very effective, heat source is an incandescent bulb. Water has a heat capacity of 1 cal/g/K = 4.184 J/g/K (forgive my mixing SI and CGS units). A 100 W bulb can heat one ounce (28 g) of water at one degree per second, at full efficiency (for example, if you set things up so the bulb is submerged).

I think that Caitlinsdad is right that a demo using water won't be very clear. The problem is that water is extremely low viscosity, so you're likely to get multiple local convection cells, turbulent mixing, and the rest, rather than a nice clean double cell flow. Something like ethylene glycol or some other transparent viscous fluid is likely to be better for your purposes.

I did a Goole search for "convection cell demo" and found a number of examples which might give you some ideas. Good luck!


4 years ago

I think a better demonstration can be made from a lava lamp design. There are many instructables or projects on the internet to make a "safer" lava lamp with common and less toxic fluids. Using food coloring as dye markers would really just muddle up the water as it dissolves into it. I don't think the heat convection would be strong enough to make it move like you see in wind tunnel or water tank testing.