kapillaarinousun

Kapillaarinousu, or capillary rise, is the upward movement of liquids in narrow tubes or porous materials driven by capillary action. It arises from the balance between cohesive forces within the liquid and adhesive forces between the liquid and solid surfaces, which creates a pull along the liquid that can lift it against gravity.

In a cylindrical capillary, the equilibrium rise height h is described by Jurin’s law: h = (2 γ cos θ) / (ρ g r). Here γ is the liquid’s surface tension, θ is the contact angle between the liquid and the tube wall, ρ is the liquid density, g is gravitational acceleration, and r is the capillary radius. If the walls are hydrophilic (θ < 90°), the liquid rises; if the walls are hydrophobic (θ > 90°), it is depressed. The rise is greater for smaller radii and higher surface tension, and it decreases with increasing density and radius.

The phenomenon also occurs in porous media such as soils and paper, enabling wicking and fluid distribution. In nature, capillary rise contributes to water transport in plant xylem and influences moisture movement in soils and building materials.

Factors that affect capillary rise include temperature (which changes γ and θ), impurities, surface roughness, and dynamic effects during rapid filling. In real systems, the rise approaches a steady state when hydrostatic pressure balances capillary pressure; contact-angle hysteresis and evaporation can modify the observed height.

Historically, capillary action has been studied since the 18th century, with Jurin’s law formalizing the height of rise and Laplace contributing to the understanding of capillary pressure.