The results of investigations concerning the tortuousity of pore channels are presented. Although the tortuousity factor is present in the famous Kozeny-Carman formula, its determination in empirical way is difficult. A variable shape tube of the constant cross-section represents the most simple tortuousity model. The relation between the exactly defined channel tortuousity and the overall hydraulic resistance was determined experimentally. Investigations were carried out applying a collection of multiple-bend and coiled tube models. It was observed that centrifugal effects related to channel tortuousity give rise to hydrodynamic phenomena represented by the non-linear correction term to the well known Darcy's law involving 3/2 exponent in flow rate.