kapillaarivuotooireyhtymä

Kapillaarivuoto, or capillary flow, is the movement of a liquid through narrow spaces such as tubes or porous materials due to capillary action. This phenomenon arises from the interplay between cohesive forces within the liquid and adhesive forces that bind the liquid to the surrounding solid surface, together with surface tension at the liquid–gas interface.

In a vertical capillary, the liquid experiences a capillary pressure given by ΔP = 2 γ cos θ / r, where γ is the liquid’s surface tension, θ is the contact angle between the liquid and the solid, and r is the capillary radius. If the contact angle is less than 90 degrees (cos θ > 0), the capillary pressure can lift the liquid against gravity. At equilibrium, the rise height is h = 2 γ cos θ /(ρ g r), with ρ the liquid density and g the acceleration due to gravity. In porous media, where the flow is more complex, the dynamic imbibition of liquid follows Washburn’s law, L^2 ≈ (r γ cos θ /(2 η)) t, where η is the liquid viscosity and t is time, describing how a liquid penetrates into a capillary network over time.

Factors influencing capillary flow include surface tension, wettability (contact angle), pore size, fluid viscosity, and temperature. Roughness and chemical heterogeneity of surfaces can lead to contact-angle hysteresis and departure from ideal behavior.

Applications span from inkjet printing and paper drying to soil moisture transport, plant xylem hydration, and various microfluidic and biomedical devices, where capillary forces are used to move or control tiny liquid volumes without external pumping.