Kapillarrohren

Kapillarrohren, also known as capillary tubes, are very narrow tubes, typically made of glass or metal, with an internal diameter of less than one millimeter. Their defining characteristic is the significant effect of surface tension on fluid behavior within them. This phenomenon, known as capillary action, allows liquids to rise or fall within the tube against gravity, or to spread out.

The forces responsible for capillary action are adhesion, the attraction between the liquid and the tube walls, and cohesion, the attraction between the liquid molecules themselves. When the adhesive forces are stronger than the cohesive forces, the liquid wets the tube and rises. Conversely, if cohesive forces dominate, the liquid may be depressed. The height to which a liquid rises or falls is inversely proportional to the diameter of the capillary tube; smaller diameters lead to greater capillary effects.

Kapillarrohren have a wide range of applications. In science and engineering, they are used in instruments like thermometers and manometers. They are also employed in chromatographic techniques for separating mixtures. In everyday life, capillary action is responsible for how water is absorbed by plants, how ink flows in a pen, and how towels soak up spills. The controlled flow and self-propelling nature of liquids in these narrow tubes make them indispensable in many technologies.