Tortuosity

The tortuosity τ (Latin tortuosus " wound ") identifies the degree of tortuosity of transport paths in the pores of porous materials. It is used for the description of various physical transport processes, and is in addition to the porosity and the permeability of a parameter for describing the properties of porous materials.

The tortuosity is defined as the square of the ratio of the average effective length of the conveying path through a porous layer to the thickness of the layer:

Occasionally, the simple ratio of the two lengths is called the tortuosity.

An alternative to physically meaningful definition of tortuosity via the mean value of the angle between the direction of the pores, and the direction of transport in a section through the porous medium:

From theoretical considerations, saving for pore space models with cylindrical pores unconnected values ​​of 2 or 3 in natural pore spaces of the values ​​depart from it in part significantly.

The transport processes of the tortuosity is used include:

• Electrical current ( electrical tortuosity )
• Flow of fluids ( hydraulic tortuosity )
• Diffusion.

The tortuosity of a particular porous material may be different for different transport processes. Thus, in a water -filled conductive porous material, the effective length of the power lines for electric power is not necessarily the same size as that of the flow lines for the flow of water.

Applies the concept of tortuosity, among others in the aquatic and Petrophysics, where the flow of water and oil is examined through porous layers of rock, and in acoustics, where the tortuosity plays a role in the characterization of the absorption effect of porous sound absorbers.