Teacup effect
The teacup effect is the movement of specifically heavier particles at the bottom of a rotating liquid towards the center.
observation
First, a liquid is set in rotation in an approximately round vessel, e.g. B. by stirring. After the end of the stirring, the turbulence introduced in this way slowly subsides and the typical rotational movement of the liquid sets in. Sediment particles in the liquid (e.g. tea leaves) that sink to the bottom are caught there by a current close to the ground and moved on spiral paths to the center of rotation. There they accumulate and are rotated on the spot in a circle with a correspondingly strong rotation.
interpretation
Due to the friction on the sole, water particles close to the sole are slowed down in their rotational movement so that they are subjected to a lower centrifugal force. Since the water particles above are subject to the greater, normal rotation, they are subject to a comparatively greater centrifugal force, which ensures that the water level outside is increased. This higher water level at the outer edge leads to increased hydrostatic pressure, which is propagated downwards and which the layer near the bottom cannot counteract, so that it escapes inwards. This creates a secondary flow that leads water downwards on the outside, above the bottom to the center, up in the center and outwards at the liquid level.
The visible effect is that specifically heavier particles tend to the bottom, are moved to the center by the flow near the bottom and remain there because the flow rising in the center can no longer lift them. The effect lasts as long as the liquid rotates and subsides with the rotation.
This secondary flow also arises in river bends and serves to explain the meander formation on rivers (Thomson, Isaachsen) or to explain the impact slope outside and sliding slope inside with an asymmetrical cross section of the river. This explains Thomson's observation that the water level rises in a river bend from the inside to the outside. Einstein uses the teacup effect to describe the meander formation and the displacement of rubble at the bottom of the river bed.
The effect described is used in technical systems to separate particles from a flow and remove them in a targeted manner in the middle in high concentration. This applies to cyclones, desander basins or round rain overflow basins (vortex shaft basins). In the latter, the teacup effect is used to guide separated sediments to the center and remove them there so that the basins are self-cleaning.
Individual evidence
- ↑ James Thomson : On the Origin of Windings of Rivers in Alluvial Plains, with Remarks on the Flow of Water round Bends in Pipes. In: Proceedings of the Royal Society of London, Ser.B 25 (1876), pp. 5-8. doi : 10.1098 / rspl.1876.0004
- ↑ J. Isaachsen: About some effects of centrifugal forces in liquids and gases. In: Zivilingenieur 42 (1896), p. 351.
- ↑ J.Isaachsen: Internal processes in flowing liquids and gases. In: Journal of the Association of German Engineers. 55 (1911), pp. 215, 263, 428, 605, 946.
- ↑ Albert Einstein: The cause of the meander formation of the rivers and the so-called Baer's law. In: Die Naturwissenschaften 14 (1926), pp. 223–224. doi : 10.1007 / BF01510300
Web links
- Tea cup effect experiments