Convection cells

Reveal the hidden patterns in liquid heat transfer!

Difficulty:
Danger:
Duration:
10 minutes
Convection cells

Safety

  • Carefully review the general safety advice in the instruction book before starting the experiment.
  • Perform the experiment on the underlay and use protective gloves.
  • Observe safety precautions when working with boiling water.
  • Avoid contact with food and dishware. Thoroughly wash or dispose of any dishware you use.

Step-by-step instructions

Use the protective underlay and safety gloves to keep your hands and desktop clean.

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Prepare the vapor bath: fill three cups with boiling water.

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Set the three liquids to heat on the vapor bath and observe closely. The hot water vapor heats the bottom of the Petri dishes, and pretty soon this heat causes the fluid to start moving. Draw your observations on the sketch paper provided.

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Disposal

  • Dispose of solid waste together with household garbage.
  • Pour liquids down the sink. Wash with an excess of water.

Scientific description

When the bottom layers of a volume of liquid are heated more than the top layers, you can observe flows that strive to equalize the temperatures by mixing the layers: the warm layer  rises, while the cold layer  sinks.

These flows appear because warm liquid  is less dense than cold liquid , and the warmer, lighter layer rises  to the surface while gravity draws the colder, denser layer  down to the bottom. This causes the liquids to mix. This type of motion is called convection, and the corresponding flows—convection flows.

When you heat the liquid with a metallic coloring in the dish, you can observe that convection features a certain order. If you look closely, you can see separate, closed elementary structures  called Rayleigh-Bénard cells. Mixing happens independently in each, and there is almost no liquid transfer between the cells.

Due to convection, the temperatures in the top and bottom layers gradually equalize, and the amount of cells changes: they can join together to form larger structures.

That’s interesting!

If you look closely at the Sun’s sizzling surface through a telescope, you will see that it is covered in granules. These granules may seem small, but each can span up to 1,500 km in size! How are they formed? They are also caused by convection currents, which are responsible for the heat transfer of plasma from the depths of the Sun.