Capillary Tubing

Definition - What does Capillary Tubing mean?

Capillary tubing or capillary tubes are very thin tubes made of a rigid material, such as plastic or glass in which a liquid flows up into the tubes against gravity in a process called capillary action (capillarity).

Capillarity is the movement of a liquid in a small cross sectional capillary passage tube such as the openings in porous materials. A fluid's capillary action can occur in both vertical and horizontal directions. In the capillarity or capillary action, the fluid moves in an upward direction against the force of gravity.

Corrosionpedia explains Capillary Tubing

In capillary tubing, capillarity occurs due to the intermolecular forces between the liquid and surrounding solid surfaces of the tube. It is caused by the pressure of cohesion and adhesion, which causes the liquid to move even against gravity.

The effect of capillary action can be seen in:

  • The drawing up of liquids between the hairs of a paintbrush
  • Thin tubes
  • Porous materials such as paper
  • Some non-porous materials, such as liquefied carbon fiber
  • Cells

Capillary action has many significant applications such as thin layer chromatography, in which a solvent moves vertically up a plate via capillary action. In brazing, capillary action causes a filler metal to be drawn into the space between work pieces.

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