Its everything about momentum– and small amounts of liquid right at the spout.
Researchers at TU Wien answer an age-old question: How can the so-called “teapot result” be described?
The “teapot result” has actually been threatening pristine white tablecloths for ages: if a liquid is put out of a teapot too gradually, then the circulation of liquid sometimes does not remove itself from the teapot, discovering its way into the cup, however dribbles down at the outside of the teapot.
This phenomenon has been studied scientifically for decades– now a research study team at TU Wien has succeeded in describing the “teapot effect” completely and in information with a fancy theoretical analysis and many experiments: An interaction of different forces keeps a small amount of liquid directly at the edge, and this suffices to redirect the circulation of liquid under particular conditions.
Now, research study on the teapot effect has come complete circle, as it was studied at Reiners alma mater, the TU Wien, by a team around Dr. Bernhard Scheichl, speaker at the Institute of Fluid Mechanics and Heat Transfer and Key Scientist at the Austrian Centre of Excellence for Tribology (AC2T research GmbH), in cooperation with the Department of Mathematics at the University College London.
The interaction of these forces is the basis of the teapot impact. The smaller this angle is or the more hydrophilic (i.e. wettable) the material of the teapot is, the more the detachment of the liquid from the teapot is slowed down.
The theoretical estimations on the teapot impact were published by the research study team in September 2021 in the Journal of Fluid Mechanics. In this way, it was possible to show precisely how the wetting of the edge listed below a crucial putting rate leads to the “teapot effect,” thus confirming the theory.
An effect with a long history
The “teapot result” was first described by Markus Reiner in 1956. Now, research on the teapot effect has actually come complete circle, as it was studied at Reiners alma mater, the TU Wien, by a team around Dr. Bernhard Scheichl, lecturer at the Institute of Fluid Mechanics and Heat Transfer and Key Scientist at the Austrian Centre of Excellence for Tribology (AC2T research GmbH), in cooperation with the Department of Mathematics at the University College London.
The teapot effect at different flow rates. Credit: TU Wien
” Although this is a relatively easy and very common effect, it is incredibly difficult to discuss it exactly within the framework of fluid mechanics,” states Bernhard Scheichl. The sharp edge on the underside of the teapot beak plays the most important function: a drop types, the location straight below the edge always remains wet. The size of this drop depends on the speed at which the liquid drains of the teapot. This drop can direct the entire flow around the edge and dribbles down on the outdoors wall of the teapot if the speed is lower than a critical threshold.
” We have actually now been successful for the very first time in offering a total theoretical description of why this drop types and why the underside of the edge always stays wetted,” says Bernhard Scheichl. The mathematics behind it is complicated– it is an interplay of inertia, capillary and viscous forces. The inertial force guarantees that the fluid tends to keep its initial direction, while the capillary forces slow the fluid down right at the beak. The interaction of these forces is the basis of the teapot result. The capillary forces ensure that the impact only begins at an extremely particular contact angle in between the wall and the liquid surface. The smaller this angle is or the more hydrophilic (i.e. wettable) the material of the teapot is, the more the detachment of the liquid from the teapot is decreased.
Tea in area
Remarkably, the strength of gravity in relation to the other forces that take place does not play a decisive role. Gravity merely determines the direction in which the jet is directed, however its strength is not definitive for the teapot impact. The teapot result would therefore likewise be observed when consuming tea on a moon base, however not on a spaceport station without any gravity at all.
The theoretical calculations on the teapot result were published by the research study group in September 2021 in the Journal of Fluid Mechanics. Now experiments were likewise carried out: Water was poured from an inclined teapot at different circulation rates and shot with high speed electronic cameras. In this way, it was possible to show exactly how the wetting of the edge below a crucial pouring rate leads to the “teapot result,” therefore confirming the theory.
Recommendation: “Developed liquid movie passing a smoothed and wedge-shaped routing edge: small analysis and the teapot impact at large Reynolds numbers” by B. Scheichl, R.I. Bowles and G. Pasias, 8 September 2021, Journal of Fluid Mechanics.DOI: 10.1017/ jfm.2021.612.
