Tortuositeetin

Tortuositeetti, commonly referred to as tortuosity in English, is a dimensionless quantity used to describe how winding or indirect a transport path is within a porous or complex medium. It characterizes the deviation of actual pathways that particles or signals must traverse from a direct straight-line route between two points.

A typical definition states that tortuositeetti is the ratio of the effective path length through the medium to the straight-line distance between the same two points. Consequently, it is always greater than or equal to one, with a value of one indicating a perfectly straight, unobstructed path. In real materials, tortuositeetti can vary with direction (anisotropy) and with the scale or region being measured.

Tortuositeetti is used to relate transport properties of a material to those of the free medium. For diffusion and electrical conduction, the effective transport coefficients are generally reduced relative to their unobstructed values, with the reduction influenced by both porosity and tortuosity. As a result, relationships such as the effective diffusion coefficient or the effective conductivity often include a tortuosity term, though the exact form depends on the system and the modeling approach.

Measurement and estimation methods include tracer diffusion experiments, impedance or conductivity tests, and image-based analyses (for example, micro-CT) that reconstruct pore networks to estimate path lengths. Numerical simulations and empirical correlations also provide tortuosity values for specific materials or applications.

Applications of tortuositeetti span hydrology, petroleum engineering, catalysis, battery and fuel-cell materials, and other fields where transport through complex microstructures is important. It remains a key parameter for understanding and modeling how geometry controls transport processes.