Kapillarradius

Kapillarradius is a term used in fluid mechanics and physiology to denote the radius of a capillary tube or a biological capillary. It is a key geometric parameter that influences fluid flow, capillary pressure, surface-tension effects and transport properties in small vessels and porous media.

In fluid mechanics and microfluidics, the Kapillarradius of a tube or pore determines capillary rise and wetting behavior according to Jurin’s law and the Young–Laplace equation. Capillary rise h is inversely proportional to the radius (h = 2γ cosθ / ρ g r), and the pressure difference across a curved liquid interface is given by ΔP = 2γ / r for a cylindrical geometry, where γ is surface tension. In viscous flow, Poiseuille’s law shows that volumetric flow rate through a cylindrical capillary scales with the fourth power of the radius, making small changes in radius strongly influential on flow resistance.

In physiology, Kapillarradius commonly refers to the internal radius of blood capillaries. Typical capillary radii are on the order of a few micrometers (often 2–5 μm), and variations affect perfusion, shear stress on endothelial cells, and exchange of solutes and gases. Vasomotion, inflammation, or structural remodeling can alter capillary radius, with implications for tissue oxygenation and disease processes.

Measurement techniques include light and electron microscopy, intravital imaging, and micro-CT for synthetic networks. Understanding Kapillarradius is important in designing microfluidic devices, interpreting microvascular function, and modeling multiphase flow in porous materials.