Hele Shaw cell

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The Hele-Shaw cell , named after its inventor Henry Selby Hele-Shaw , was developed to experimentally produce fractal structures in rheology with simple means.

construction

The Hele-Shaw cell consists of two square, usually transparent panes (mostly plexiglass ). One of them has a hole in the middle. Both discs are pressed together evenly at the edge. If this is not the case, other means, for example a filter paper circle , must be used to guarantee an even pressure distribution in the cell or an even distance between the panes.

Test execution

There are two types of experiment:

  • One is to evenly coat a disc with a highly viscous liquid. Then both panes are pressed together and then pulled apart vertically. The liquid forms fractal structures on both discs.
  • In the second variant of the experiment, a highly viscous liquid is first injected through the central hole into the cell until it reaches near the edge. Then a liquid with a lower viscosity than the first is injected into the cell. This in turn creates fractal structures. In order to be able to distinguish the two liquids, they have different colors.

What happens when you try?

The more viscous, i.e. more viscous liquid (e.g. honey , soap , butter ), which was previously pressed into the Hele Shaw cell, is penetrated by the less viscous liquid (e.g. water with coloring agents ) at certain points . These points are indentations which occur randomly due to irregular and unregulated fluctuations in the test conditions. Finger-shaped canals are formed that continue to split. A pattern of increasingly finely branched channels emerges, a so-called fractal.

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